WO2007023293A2

WO2007023293A2 - Luminescent material compositions and structures incorporating the same

Info

Publication number: WO2007023293A2
Application number: PCT/GB2006/003177
Authority: WO
Inventors: Jörg Peter FEIST; John Raymond Nicholls; Michael James Fraser; Andrew Lawrence Heyes; Stephen John Skinner
Original assignee: Southside Thermal Sciences (Sts) Limited
Priority date: 2005-08-24
Filing date: 2006-08-24
Publication date: 2007-03-01
Also published as: WO2007023293A3; US9045830B2; EP1928977A2; EP1928977B1; US20090202864A1

Abstract

Luminescent material compositions, in particular for use in high-temperature environments, and structures, such as thermal barrier coatings (TBCs), which incorporate the same.

Description

LUMINESCENT MATERIAL COMPOSITIONS AND STRUCTURES INCORPORATING THE SAME

The present invention relates to luminescent material compositions, in particular for use in high-temperature environments, and structures, such as thermal barrier coatings (TBCs)₇ which incorporate the same.

TBCs are structural coatings which are applied to components which are subjected to high temperatures, often greater than 1000 C, and thus would be prone inter alia to oxidation and corrosion processes. Typical applications are in the aviation and power generation industries, particularly in the coating of turbine components, such as vanes and blades.

Gas turbines have been used to power aircraft and in the production of electricity since their invention in 1939. There has been a continuous drive to increase fuel efficiency, with fuel consumption having more than halved over the last three or four decades. This has been achieved principally by increasing firing temperatures. Apart from new alloys and cooling methods, TBCs have played a major role in this development. These coatings were first used on jet engines in the 1970's and are now a common feature on power generation turbines. The use of TBCs allows turbines to be operated at temperatures above the melting point of the metal components in the hot section, such as vanes and blades, thereby increasing efficiency and reducing CO₂ emissions.

Existing TBCs are predominantly formed from yttria-stabilized zirconia (YSZ), though other ceramic materials, such as pyrochlores, are now being considered, and provide thermal insulation and oxidation protection on turbine blades, vanes and combustion chamber liners in gas turbines used in power generation and aviation.

As disclosed in the applicant's earlier WO-A-00/06796, the provision of luminescent materials in TBCs enables the in situ optical measurement of characteristics of the TBCs, in particular the temperature of the TBCs. Such measurement of characteristics of TBCs is of great advantage, but there is a limit to the operating temperature of existing luminescence systems.

It is an aim of the present invention to provide luminescent material compositions which are operative in higher-temperature environments, typically those in excess of 1000 C, and ideally in the range of from 1000 to 1600 C, and structures which incorporate the same. It is also desirable that the luminescent material compositions provide for a repeatable measurement with a high degree of accuracy.

In one aspect the present invention provides a luminescent material composition comprising a first, structural or matrix phase, a second phase within the matrix phase, and at least one luminescent dopant.

In another aspect the present invention provides a structure comprising a main, structural or matrix phase, and a plurality of discrete, luminescent atomic clusters or particles which are distributed within the structural phase and act, when excited by an excitation signal, to emit a luminescence signal which is representative of one or more characteristics of the structure.

In a further aspect the present invention provides a luminescent material composition comprising a YAG-based host phase and at least one luminescent dopant.

In a still further aspect the present invention provides a luminescent material composition comprising a YAP-based host phase and at least one luminescent dopant.

In a yet further aspect the present invention provides a luminescent material composition comprising a GdAIO₃-based host phase and at least one luminescent dopant. In a still yet further aspect the present invention provides a luminescent material composition which comprises an A₂B₂O₇ (pyrochlore) host phase which is doped with at least one luminescent dopant, where A comprises one or more elements selected from the lanthanide series or the actinide series and B comprises one or more elements selected from the group of transition metals.

Preferred embodiments of the present invention will now be described hereinbe.low by way of example only with reference to the accompanying drawings, in which:

Figure 1 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising a YAG host phase which is doped with Tb in an amount of 5 mol%;

Figure 2 illustrates the optical spectra for a material composition comprising a YAG host phase which is doped with Eu in an amount of 5 mol% as plasma sprayed (I) and following annealing (II);

Figure 3 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figure 2 as plasma sprayed and prior to annealing;

Figure 4 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figure 2 following annealing;

Figure 5 illustrates the optical spectra for a material composition comprising a YAG host phase which is doped with Tm in an amount of 5 mol% as plasma sprayed (I) and following annealing (II);

Figure 6 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figure 5 as a plasma-sprayed powder and following annealing; Figure 7 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figure 5 as a plasma-sprayed coating and following annealing;

Figure 8 illustrates the optical spectra for a material composition comprising a YAG host phase which is doped with Dy in an amount of 5 mol% as plasma sprayed (I) and following annealing (II);

Figure 9 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figure 8 as plasma sprayed and prior to annealing;

Figure 10 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figure 8 following annealing;

Figure 11 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising a YAG host phase which is doped with Dy in an amount of 3 mol% as plasma sprayed and following annealing;

Figure 12 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising a YAG host phase which is doped with Sm in an amount of 5 mol% as plasma sprayed and following annealing;

Figure 13 illustrates the optical spectra for a material composition comprising a YAP host phase which is doped with Dy in an amount of 0.3 mol% as plasma sprayed (I) and following annealing (II);

Figure 14 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figure 13 following annealing;

Figure 15 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising a YAP host phase which is doped with Eu in an amount of 0.3 mol% as plasma sprayed and following annealing;

Figure 16 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising a YAP host phase which is doped with Sm in an amount of 0.3 mol% as plasma sprayed and following annealing;

Figure 17 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising a GdAIO₃ host phase which is doped with Dy in an amount of 1 mol% as plasma sprayed and following annealing;

Figure 18 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising a GdAIO₃ host phase which is doped with Sm in an amount of 1 mol% as plasma sprayed and following annealing;

Figure 19 illustrates a plot of the life-time decay as a function of temperature for material compositions comprising an La₂Zr₂O₇ (pyrochlore) host phase which is doped with Tb in an amount of 1 mol%, 5 mol% and 10 mol%;

Figure 20 illustrates a plot of the life-time decay as a function of temperature for material compositions comprising an La₂Zr₂O₇ (pyrochlore) host phase which is doped with Tb in amounts of 5 mol% and 10 mol%, a material composition comprising an La₂Zr₂O₇ (pyrochlore) host phase which is doped with Eu in an amount of 5 mol%, and a material composition comprising an La₂Zr₂O₇ (pyrochlore) host phase which is doped with Dy in an amount of 10 mol%;

Figure 21 schematically represents a structure in accordance with a preferred embodiment of the present invention; Figure 22 illustrates an XRD pattern for a material composition comprising 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based luminescent phase which is doped with Tb in an amount of 5 mol%;

Figure 23 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figure 22, and a material composition comprising a YAG host phase which is doped with Tb in an amount of 5 mol%;

Figure 24 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based second phase which is doped with Eu in an amount of 5 mol%, and a material composition comprising a YAG host phase which is doped with Eu in an amount of 5 mol%;

Figure 25 illustrates a scanning electron micrograph (SEM) of a material composition comprising 95 wt% of a YSZ matrix phase and 5 wt% of a YAG- based second, luminescent phase which is doped with Dy in an amount of 5 mol%;

Figure 26 illustrates the optical spectra for the YAG-based luminescent phase of the material composition of Figure 25 (I) and a single-phase YAG- based luminescent material composition doped with Dy in an amount of 3 mol% (II);

Figures 27 to 30 illustrate XRD patterns for a material composition comprising 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based luminescent phase which is doped with Dy in an amount of 3 mol%;

Figure 31 illustrates a plot of the life-time decay as a function of temperature for the material composition of Figures 27 to 30 as prepared by the precipitation route (I) and subsequent to being subjected to thermal cycling (II); Figure 32 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based luminescent phase which is doped with Dy in an amount of 3 mol% as prepared by the precipitation route and subsequent to being subjected to thermal cycling;

Figures 33 and 34 illustrate XRD patterns for a material composition comprising 90 wt% of a YSZ matrix phase and 10 wt% of a YAG-based luminescent phase which is doped with Dy in an amount of 5 mol% as sprayed and following annealing, respectively;

Figure 35 illustrates a sectional scanning electron micrograph (SEM) of the material composition of Figures 33 and 34;

Figure 36 illustrates a sectional scanning electron micrograph (SEM) of a material composition comprising 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based luminescent phase which is doped with Eu in an amount of 5 mol%; and

Figure 37 illustrates a sectional scanning electron micrograph (SEM) of a material composition comprising 80 wt% of a YSZ matrix phase and 20 wt% of a YAG-based luminescent phase which is doped with Tm in an amount of 5 mol%.

(P Single-Phase Materials

In this aspect the present invention relates to a plurality of single-phase luminescent materials, which provide for luminescence to elevated temperatures, in particular 1000 C, as compared to the state of the art.

fa) YAG Material Compositions In this aspect the present invention relates to a luminescent material composition comprising a YAG-based host phase and at least one luminescent dopant.

In one embodiment the YAG-based host phase comprises Y₃AI₅O₁₂.

In another embodiment the YAG-based host phase comprises Y₃Al_xFe_5-x0i₂, where X > 0.

In one embodiment the at least one luminescent dopant comprises one or more elements selected from the lanthanide series (rare earth metals).

Preferably, the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

In one embodiment the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

In another embodiment the at least one luminescent dopant is doped in an amount of between 0.5 mol% and 6 mol%.

In a further embodiment the at least one luminescent dopant is doped in an amount of between 3 mol% and 6 mol%.

In a still further embodiment the at least one luminescent dopant is doped in an amount of between 4.5 mol% and 5.5 mol%.

In a yet further embodiment the at least one luminescent dopant is doped in an amount of about 3 mol%.

In a still yet further embodiment the at least one luminescent dopant is doped in an amount of about 5 mol%. In one embodiment the luminescent material composition is incorporated in a structure, in a preferred embodiment as a coating, and more particularly as a thermal barrier coating.

In one embodiment the coating is a multi-layer coating, of which one layer comprises the luminescent material composition.

This embodiment of the present invention will now be described with reference to the following non-limiting Examples.

Example IA

In this Example, a material composition is presented which comprises a YAG phase which is doped with Tb in an amount of 5 mol%.

In one embodiment the doped YAG phase can be produced by plasma spraying, typically air plasma spraying, precursor powders. In this embodiment the material as plasma sprayed is not fully crystalline, and an annealing step is subsequently performed at a temperature above the crystallisation temperature, in this embodiment at 915 C, to cause crystallization.

In another embodiment the doped YAG phase can be produced by solution chemistry, such as by the Pechini process or by urea precipitation.

In a further embodiment the doped YAG phase can be produced by a solid state reaction, in which a mixture of oxides or carbonates are heated to a high temperature.

Figure 1 illustrates a plot of the life-time decay as a function of temperature for this material composition, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 543 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to at least 1200 C as compared to existing luminescence systems.

Example IB

In this Example, a material composition is presented which comprises a YAG phase which is doped with Eu in an amount of 5 mol%.

In one embodiment, as in this embodiment, the doped YAG phase can be produced by plasma spraying, typically air plasma spraying, precursor powders. In this embodiment the material as plasma sprayed is not fully crystalline, and an annealing step is subsequently performed at a temperature above the crystallisation temperature, in this embodiment at 915 C, to cause crystallization.

Figure 2 illustrates the optical spectra for this material composition as plasma sprayed (I) and subsequently annealed (II), where utilizing an excitation wavelength of 266 nm. As can be clearly observed, the material as plasma sprayed has an amorphous state, and, following annealing, the material has a crystalline state.

Figure 3 illustrates a plot of the life-time decay as a function of temperature for this material composition as plasma sprayed and prior to annealing, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 617 nm. As will be observed, the life-time decay shows an intermediate dip, here at a temperature of about 400 C, which is indicative of the material not being fully crystalline. Figure 4 illustrates a plot of the life-time decay as a function of temperature for this material composition following annealing, where utilizing an excitation wavelength of 266 nm and observed at wavelengths of 597.5 nm and 717 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of at least 1300 C as compared to existing luminescent systems.

Example 1C

In this Example, a material composition is presented which comprises a YAG phase which is doped with Tm in an amount of 5 mol%.

Figure 5 illustrates the optical spectra for this material composition as plasma sprayed (I) and subsequently annealed (II), where utilizing an excitation wavelength of 355 nm. As can be clearly observed, the material as plasma sprayed has an amorphous state, and, following annealing, the material has a crystalline state. Figures 6 and 7 illustrate plots of the life-time decay as a function of temperature for this material composition for a powder and a coating as plasma sprayed and following annealing, where utilizing an excitation wavelength of 355 nm and observed at a wavelength of 455 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1500 C as compared to existing luminescent systems, with there being no difference in powders and coatings.

Example ID

In this Example, a material composition is presented which comprises a YAG phase which is doped with Dy in an amount of 5 mol%.

Figure 8 illustrates the optical spectra for this material composition as plasma sprayed (I) and subsequently annealed (II), where utilizing an excitation wavelength of 355 nm. As can be clearly observed, the material as plasma sprayed has an amorphous state, and, following annealing, the material has a crystalline state. Figure 9 illustrates a plot of the life-time decay as a function of temperature for this material composition as plasma sprayed and prior to annealing, where utilizing an excitation wavelength of 355 nm and observed at a wavelength of 581 nm. As will be observed, the life-time decay shows an intermediate dip, here at a temperature of about 700 C, which is indicative of the material not being fully crystalline.

Figure 10 illustrates a plot of the life-time decay as a function of temperature for this material composition following annealing, where utilizing an excitation wavelength of 355 nm and observed at a wavelength of 580 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1500 C as compared to existing luminescent systems.

Example IE

In this Example, a material composition is presented which comprises a YAG phase which is doped with Dy in an amount of 3 mol%.

In a further embodiment the doped YAG phase can be produced by a solid state reaction, in which a mixture of oxides or carbonates are heated to a high temperature. Figure 11 illustrates a plot of the life-time decay as a function of temperature for this material composition following annealing, where utilizing an excitation wavelength of 355 nm and observed at a wavelength of 580 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1400 C as compared to existing luminescent systems.

Example IF

In this Example, a material composition is presented which comprises a YAG phase which is doped with Sm in an amount of 5 mol%.

Figure 12 illustrates a plot of the life-time decay as a function of temperature for this material composition, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 622 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1200 C as compared to existing luminescent systems.

(b) YAP Material Compositions In this aspect the present invention relates to a luminescent material composition comprising a YAP-based host phase and at least one luminescent dopant.

In one embodiment the YAP-based host phase comprises YAIO₃.

In one embodiment the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

In one embodiment the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

In another embodiment the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 3 mol%.

In a further embodiment the at least one luminescent dopant is doped in an amount of about 0.3 mol%.

In a still further embodiment the at least one luminescent dopant is doped in an amount of about 1 mol%.

In one embodiment the luminescent material composition is incorporated in a structure, in a preferred embodiment as a coating, and more particularly as a thermal barrier coating.

In one embodiment the coating is a solid, continuous coating.

In another embodiment the coating is a paint coating. In one embodiment the coating is a multi-layer coating, of which one layer comprises the luminescent material composition.

Example 2A

In this Example, a material composition is presented which comprises a YAP phase which is doped with Dy in an amount of 0.3 mol%.

In one embodiment, as in this embodiment, the doped YAP phase can be produced by plasma spraying, typically air plasma spraying, precursor powders. In this embodiment the material as plasma sprayed is not fully crystalline, and an annealing step is subsequently performed at a temperature above the crystallisation temperature, in this embodiment at 915 C, to cause crystallization.

In another embodiment the doped YAP phase can be produced by solution chemistry, such as by the Pechini process or by urea precipitation.

In a further embodiment the doped YAP phase can be produced by a solid state reaction, in which a mixture of oxides or carbonates are heated to a high temperature.

Figure 13 illustrates the optical spectra for this material composition as plasma sprayed (I) and subsequently annealed (II), where utilizing an excitation wavelength of 355 nm. As can be clearly observed, the material as plasma sprayed has an amorphous state, and, following annealing, the material has a crystalline state.

Figure 14 illustrates a plot of the life-time decay as a function of temperature for this material composition following annealing, where utilizing an excitation wavelength of 355 nm and observed at wavelengths of 581.5 nm, 610 nm and 721 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1250 C as compared to existing luminescent systems.

Example 2B

In this Example, a material composition is presented which comprises a YAP phase which is doped with Eu in an amount of 0.3 mol%.

Figure 15 illustrates a plot of the life-time decay as a function of temperature for this material composition following annealing, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 622 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1150 C as compared to existing luminescent systems.

Example 2C

In this Example, a material composition is presented which comprises a YAP phase which is doped with Sm in an amount of 0.3 mol%. In one embodiment, as in this embodiment, the doped YAP phase can be produced by plasma spraying, typically air plasma spraying, precursor powders. In this embodiment the material as plasma sprayed is not fully crystalline, and an annealing step is subsequently performed at a temperature above the crystallisation temperature, in this embodiment at 915 C, to cause crystallization.

Figure 16 illustrates a plot of the life-time decay as a function of temperature for two measurements for this material composition following annealing, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 573 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1350 C as compared to existing luminescent systems.

(c) GdAICh Material Compositions

In this aspect the present invention relates to a luminescent material composition comprising a GdAIO₃-based host phase and at least one luminescent dopant.

In one embodiment the GdAIO₃-based host phase comprises GdAIO₃.

In one embodiment the at least one luminescent dopant comprises one or more elements selected from the lanthanide series. In one embodiment the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

In one embodiment the coating is a solid, continuous coating.

In another embodiment the coating is a paint coating.

Example 3A

In this Example, a material composition is presented which comprises a GdAIO₃ phase which is doped with Dy in an amount of 1 mol%. In one embodiment, as in this embodiment, the doped GdAIO₃ phase can be produced by plasma spraying, typically air plasma spraying, precursor powders. In this embodiment the material as plasma sprayed is not fully crystalline, and an annealing step is subsequently performed at a temperature above the crystallisation temperature to cause crystallization.

In another embodiment the doped GdAIO₃ phase can be produced by solution chemistry, such as by the Pechini process or by urea precipitation.

In a further embodiment the doped GdAIO₃ phase can be produced by a solid state reaction, in which a mixture of oxides or carbonates are heated to a high temperature.

Figure 17 illustrates a plot of the life-time decay as a function of temperature for this material composition following annealing, where utilizing an excitation wavelength of 355 nm and observed at a wavelength of 590.5 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to at least about 1300 C as compared to existing luminescent systems.

Example 3B

In this Example, a material composition is presented which comprises a GdAIO₃ phase which is doped with Sm in an amount of 1 mol%.

In one embodiment, as in this embodiment, the doped GdAIO₃ phase can be produced by plasma spraying, typically air plasma spraying, precursor powders. In this embodiment the material as plasma sprayed is not fully crystalline, and an annealing step is subsequently performed at a temperature above the crystallisation temperature to cause crystallization.

In another embodiment the doped GdAIO₃ phase can be produced by solution chemistry, such as by the Pechini process or by urea precipitation. In a further embodiment the doped GdAIO₃ phase can be produced by a solid state reaction, in which a mixture of oxides or carbonates are heated to a high temperature.

Figure 18 illustrates a plot of the life-time decay as a function of temperature for this material composition following annealing, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 622 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to at least about 1200 C as compared to existing luminescent systems.

(d) Pyrochlore Material Compositions

In this aspect the present invention relates to material compositions which comprise an A₂B₂O₇ (pyrochlore) host phase which is doped with at least one luminescent dopant selected from the elements Pr and Tb, where A comprises one or more elements from the lanthanide series (rare earth metals) or the actinide series and B comprises one or more elements from the group of transition metals.

In one embodiment the at least one luminescent dopant comprises Tb.

In another embodiment the at least one luminescent dopant comprises Pr.

In a further embodiment the at least one luminescent dopant comprises Pr and Tb in combination.

In one embodiment the host phase is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

In another embodiment the host phase is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant. In a further embodiment the host phase is doped with between 3 mol% and 7 mol% of the at least one luminescent dopant.

In a still further embodiment the host phase is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

In a yet further embodiment the host phase is doped with about 5 mol% of the at least one luminescent dopant.

This embodiment of the present invention will now be described with reference to the following non-limiting Example.

Example 4

In this Example, three material compositions are presented which comprise an La₂Zr₂O₇ (pyrochiore) host phase which is doped with Tb in an amount of 1 mol%, 5 mol% and 10 mol%.

Figure 19 illustrates a plot of the life-time decay for these material compositions as a function of temperature, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 543 nm. As is clearly illustrated, the material composition which is doped with 5 mol% Tb surprisingly operates at markedly-increased temperatures of up to about 1200 C, whereas the material compositions which are doped with 1 mol % Tb and 10 mol% Tb only operate up to temperatures of about 800 C.

For comparison, Figure 20 illustrates a plot of the life-time decay as a function of temperature for the same material compositions which are doped with Tb in an amount of 5 mol% and 10 mol%, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 543 nm, a composition comprising an La₂Zr₂O₇ (pyrochiore) host phase which is doped with Eu in an amount of 5 mol%, where utilizing an excitation wavelength of 266 nm and observed at a wavelength of 543 nm, and a material composition comprising an La₂Zr₂O₇ (pyrochiore) host phase which is doped with Dy in an amount of 10 mol%, where utilizing an excitation wavelength of 355 nm and observed at wavelengths of 455 nm and 582 nm.

As is clearly illustrated in Figure 20, an equivalent amount of another lanthanide dopant, namely Eu, does not provide the same effect as the Tb dopant. Indeed, that material composition is capable of operating at temperatures of only up to about 650 C.

(H) Multi-Phase Materials

In this aspect the present invention relates to luminescent material compositions which comprise a plurality of separate, discrete phases, at least one of which is luminescent and can comprise any of the above- described single-phase materials.

Figure 21 schematically represents a structure in accordance with a preferred embodiment of the present invention.

In this embodiment the structure 3 is a coating, here a TBC, as applied to a component 5, which typically operates in high-temperature environments.

The structure 3 comprises a luminescent material composition comprising a first, structural or matrix phase 3a, and a second, luminescent phase 3b which is distributed within the matrix phase 3a.

In one embodiment the structural phase 3a comprises a zirconia-based phase.

In one embodiment the zirconia-based phase comprises yttria stabilized zirconia (YSZ).

In another embodiment the zirconia-based phase comprises partially stabilized zirconia In a further embodiment the zirconia-based phase comprises zirconia stabilized with from about 3 mol% to about 6 mol% yttria, and preferably 4 mol% yttria, which is a t' structure.

In a still further embodiment the zirconia-based phase comprises zirconia stabilized with from about 6 mol% to about 10 mol% yttria, and preferably 8 mol% yttria, which is a cubic structure.

In one embodiment the zirconia-based. phase includes at least one luminescent dopant.

In one embodiment the lanthanide dopant comprises a single dopant selected from the elements Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

In another embodiment the lanthanide dopant comprises a pair of dopants selected from the pairs of elements Gd and Er, Gd and Nd, Gd and Yb, Yb and Nd and Yb and Sm.

In a yet further embodiment the zirconia-based phase comprises a zirconate pyrochlore (A₂Zr₂O₇), where A is preferably one or more elements selected from the lanthanide series.

In one embodiment A comprises one or more of the elements Gd, La, Nd and Sm.

In one embodiment the luminescent phase 3b comprises a host phase which contains Y and Al.

In one embodiment the luminescent phase 3b comprises a host phase which includes yttria and an aluminate. In another embodiment the luminescent phase 3b comprises a YAG-based host phase.

In one embodiment the YAG-based phase comprises Y₃AI₅Oi₂.

In another embodiment the YAG-based phase comprises Y₃Al_xFe₅-_xOi₂, where X > O.

In one embodiment the YAG-based phase includes at least one luminescent dopant.

In a yet further embodiment the at least one luminescent dopant is doped in an amount of about 3 mol%. In a still yet further embodiment the at least one luminescent dopant is doped in an amount of about 5 mol%.

In a further embodiment the luminescent phase 3b comprises a YAP-based host phase.

In one embodiment the YAP-based phase comprises YAIO₃.

In a still further embodiment the luminescent phase 3b comprises a GdAIO₃- based host phase.

In one embodiment the GdAIO₃-based phase comprises GdAIO₃.

In one embodiment the GdAIO₃-based phase includes at least one luminescent dopant. In one embodiment the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

In yet another embodiment the luminescent phase 3b comprises an A₂B₂O₇ (pyrochlore) host phase, where A comprises one or more elements selected from the lanthanide series or the actinide series and B comprises one or more elements selected from the group of transition metals.

In one embodiment A comprises one or more of the elements Gd, La, Nd and Sm.

In another embodiment B comprises the element Zr.

In one embodiment the pyrochlore phase includes at least one luminescent dopant. In one embodiment the at least one luminescent dopant is selected from Pr and Tb.

In one embodiment the at least one luminescent dopant comprises Tb.

In another embodiment the at least one luminescent dopant comprises Pr.

In one embodiment the pyrochlore phase is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

In another embodiment the pyrochlore phase is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant.

In a further embodiment the pyrochlore phase is doped with between 3 mol% and 7 mol% of the at least one luminescent dopant.

In a still further embodiment the pyrochlore phase is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

In a yet further embodiment the pyrochlore phase is doped with about 5 mol% of the at least one luminescent dopant.

In still yet another embodiment the luminescent phase 3b comprises an yttria-based host phase.

In one embodiment the yttria-based phase comprises yttria.

In one embodiment the yttria-based phase includes at least one luminescent dopant. In one embodiment the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

In another embodiment the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

In a further embodiment the at least one luminescent dopant is doped in an amount of between 0.5 mol% and 6 mol%.

In a still further embodiment the at least one luminescent dopant is doped in an amount of between 3 mol% and 6 mol%.

In a yet further embodiment the at least one luminescent dopant is doped in an amount of between 4.5 mol% and 5.5 mol%.

In still another embodiment the at least one luminescent dopant is doped in an amount of about 3 mol%.

In a still yet further embodiment the at least one luminescent dopant is doped in an amount of about 5 mol%.

In one embodiment the luminescent phase 3b comprises a plurality of separate, discrete atomic clusters or particles which are distributed within the structural phase 3a and act, when excited by an excitation signal, to emit a luminescence signal which is representative of one or more characteristics of the structure, in particular environmental characteristics, such as temperature. In one embodiment the clusters or particles are clusters or particles which are able to co-exist in the structural phase 3a, preferably at temperatures exceeding 1000 C.

In one embodiment the size and distribution of the clusters or particles is such as not significantly to alter the physical or chemical characteristics of the structural phase 3a, but yet sufficient to provide a luminescence signal.

In one embodiment the clusters or particles have a generally uniform shape.

In one embodiment the clusters or particles are of an average size between 1 nm and 5 μm.

In another embodiment the clusters or particles are of an average size between 1 nm and 2 μm.

In a further embodiment the clusters or particles are of an average size between 1 nm and 1 μm.

In a still further embodiment the clusters or particles are of an average size between 1 nm and 100 nm.

In a yet further embodiment the clusters or particles are of an average size between 1 nm and 50 nm.

In yet another embodiment the clusters or particles are of an average size between 20 nm and 50 nm.

In still another embodiment the clusters or particles are of an average size between 1 nm and 20 nm.

In still yet another embodiment the clusters or particles are of an average size between 1 nm and 10 nm. In another embodiment the clusters or particles have an asymmetric shape.

In one embodiment the clusters or particles have an elongate or ribbon shape.

In one embodiment the clusters or particles have an average length of less than about 150 μm.

In another embodiment the clusters or particles have an average length of less than about 100 μm.

In a further embodiment the clusters or particles have an average length of less than about 50 μm.

In one embodiment the clusters or particles have an average thickness of less than about 20 μm.

In another embodiment the clusters or particles have an average thickness of less than about 10 μm.

In a further embodiment the clusters or particles have an average thickness of less than about 5 μm.

In one embodiment the structure 3 contains the second phase in an amount between 0.1 wt% and 50 wt%.

In another embodiment the structure 3 contains the second phase in an amount between 0.1 wt% and 20 wt%.

In a further embodiment the structure 3 contains the second phase in an amount between 0.1 wt% and 10 wt%.

In a still further embodiment the structure 3 contains the second phase in an amount between 0.1 wt% and 5 wt%. In a yet further embodiment the structure 3 contains the second phase in an amount between 0.1 wt% and 2 wt%.

In yet another embodiment the structure 3 contains the second phase in an amount between 0.1 wt% and 1 wt%.

In one embodiment the luminescent phase 3b is a substantially crystalline phase.

In another embodiment the luminescent phase 3b is at least partially an amorphous phase.

In a further embodiment the luminescent phase 3b is an amorphous phase.

In one embodiment the luminescent phase 3b is a phase which is chemically and physically stable at temperatures of up to about 1700 C, and preferably when thermally cycled.

In one embodiment the structure 3 is plasma sprayed from precursor powders of the first, matrix phase and the second phase.

In another embodiment the structure 3 is formed by co-precipitation from a solution containing precursor materials in stoichiometric amounts.

In one embodiment the structure 3 could be a multi-layer coating, one layer of which includes the luminescent phase 3b.

In one embodiment the structure 3 comprises a first, lower layer which comprises substantially only the structural phase 3a, and a second, upper layer which comprises the structural phase 3a and the luminescent phase 3b distributed therewithin.

In one embodiment the coating is a solid, continuous coating. In one embodiment a bondcoat, for example, of AI₂O₃, can be incorporated at the surface of the component 5, such as to promote adhesion of the structure 3 to the component 5. In one embodiment an AI₂O₃ can be formed by thermal growth from an alloy, for example, MCrAIY (where M is a metal), or an intermetallic compound, for example, platinum aluminide.

These embodiments of the present invention will now be described with reference to the following non-limiting Examples.

Example 5A

In this Example, a material composition is presented which comprises 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based second, luminescent phase which is doped with Tb in an amount of 5 mol%.

In this embodiment the doped YAG phase is produced by a solid state reaction, in which a mixture of oxides or carbonates are heated to a high temperature.

In another embodiment the doped YAG phase could be produced by solution chemistry, such as by the Pechini process or by urea precipitation, where the material components are co-precipitated from a solution of precursor materials in stoichiometric proportions.

Figure 22 illustrates an XRD pattern for this material composition, with the XRD pattern showing the first, YSZ matrix phase and a second, discrete YAG-based phase. Peaks at 25.59, 26.94, 28.82, 32.82, 39.02, 40.10, 43.37 and 44.82, which characterize the material composition, have to date not been attributed.

Figure 23 illustrates a plot of the life-time decay as a function of temperature for this material composition and a material composition comprising a YAG host phase which is doped with Tb in an amount of 5 mol%, where both utilizing an excitation wavelength of 266 nm and observed at a wavelength of 543 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1200 C as compared to existing luminescence systems, which can also be contrasted with a YSZ host phase where doped to the same amount.

Example 5B

In this Example, a material composition is presented which comprises 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based second, luminescent phase which is doped with Eu in an amount of 5 mol% on the Y site.

Figure 24 illustrates a plot of the life-time decay as a function of temperature for this material composition and a material composition comprising a YAG host phase which is doped with Eu in an amount of 5 mol%, where both utilizing an excitation wavelength of 266 nm and observed at a wavelength of 611 nm. As is clearly illustrated, the exemplified material composition operates at markedly-increased temperatures of up to about 1250 C as compared to existing luminescent systems, and the luminescence properties of the luminescent phase are not degraded as compared to the luminescent phase where utilized as a single phase. Example 5C

In this Example, a material composition is presented which comprises 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based second, luminescent phase which is doped with Dy in an amount of 5 mol%.

In this embodiment the doped YAG phase is produced by solution chemistry, such as by the Pechini process or by urea precipitation, where the material components are co- precipitated from a solution of precursor materials in stoichiometric proportions.

In another embodiment the doped YAG phase could be produced by a solid state reaction, in which a mixture of oxides or carbonates are heated to a high temperature.

Figure 25 illustrates a high-resolution scanning electron micrograph (SEM) of this material composition. This SEM shows the two phases, where the YSZ phase comprises the larger particles, which have an average size of between about 100 nm and about 200 nm, and the doped YAG phase comprises the smaller, nanoparticles, which have an average size of between about 20nm and about 50 nm, and are located substantially at the interstices of the larger YSZ particles.

Figure 26 illustrates the optical spectra for the YAG-based luminescent phase of this material composition (I) and, for purposes of comparison, a YAG-based luminescent material composition which is doped with Dy in an amount of 3 mol% and formed separately as a discrete, single phase (II). As can be clearly observed, the YAG-based luminescent phase of this material composition has an amorphous state, which is in marked contrast to the crystalline state of a separately-formed YAG-based luminescent material composition.

Example 5D In this Example, a material composition is presented which comprises 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based second, luminescent phase which is doped with Dy in an amount of 3 mol%.

In this embodiment the doped YAG phase is produced by solution chemistry, such as by the Pechini process or by urea precipitation, where the material components are co-precipitated from a solution of precursor materials in stoichiometric proportions.

Figures 27 to 30 illustrate XRD patterns for this material composition, with the XRD patterns showing the first, YSZ matrix phase and the second, discrete YAG-based luminescent phase. Figure 27 illustrates the XRD pattern for the material composition at room temperature. Figure 28 illustrates the XRD pattern for the material composition following a heat treatment at 1200 C for 2 hours. Figure 29 illustrates the XRD pattern for the material composition following two separate heat treatments at 1200 C for 12 hours. Figure 30 illustrates the XRD pattern for the material composition following a first heat treatment at 1200 C for 24 hours and a second heat treatment at 1400 C for 12 hours.

Figures 27 to 30 clearly illustrate the stability of the second, YAG-based luminescent phase when subjected to high temperatures.

Figure 31 illustrates a plot of the life-time decay as a function of temperature for this material composition as prepared by the precipitation route (I) and subsequent to being subjected to thermal cycling to 1200 C (II), where both utilizing an excitation wavelength of 355 nm and observed at a wavelength of 581 nm. As will also be observed, the life-time decays each show an intermediate dip, here at a temperature of about 600 C. This intermediate dip is indicative of the material not being fully crystalline and being at least partly amorphous, but the repeatability of the life-time decay following thermal cycling to a temperature exceeding the crystallization temperature of the doped YAG phase indicates that this phase has a stable structure.

Figure 32 illustrates a plot of the life-time decay as a function of temperature for a material composition comprising 95 wt% of a YSZ matrix phase and 5 wt% of a YAG-based luminescent phase which is doped with Dy in an amount of 3 mol% as prepared by the precipitation route and subsequent to being subjected to thermal cycling. This material composition exhibits a similar intermediate dip in the life-time decay. As is clearly illustrated, the exemplified material composition operates at markedly- increased temperatures of up to about 1400 C as compared to existing luminescent systems.

Example 5E

In this Example, a material composition is presented which comprises 90 wt% of a YSZ matrix phase and 10 wt% of a YAG-based second, luminescent phase which is doped with Dy in an amount of 3 mol% on the Y site.

In this embodiment the material composition is produced, here as a coating, by plasma spraying, typically air plasma spraying, precursor powders, here substantially spherical particles having a particle size distribution of from about 20 μm to about 80 μm. In this embodiment the material as plasma sprayed is not fully crystalline, and an annealing step is subsequently performed at a temperature above the crystallisation temperature, in this embodiment at 915 C, to cause crystallization.

Figures 33 and 34 illustrate XRD patterns for this material composition as sprayed and following annealing, respectively. The XRD pattern of Figure 33 shows a crystalline YSZ matrix phase, but shows a non-crystalline YAG phase, as represented by the background intensity at 2Θ angles of about 30 degrees and between about 40 and about 60 degrees. This XRD pattern can be contrasted with that of Figure 34 which shows a crystalline YSZ matrix phase and a crystalline YAG phase.

In the XRD pattern of Figure 33, the 2Θ peaks are located at angles 18.0048, 27.7008, 28.1641, 30.1321, 33.2566, 34.7211, 35.0479, 36.5325, 41.0334, 42.9965, 46.4882, 50.2383, 50.5156, 52.7092, 55.0006, 55.1489, 56.1425, 56.2944, 57.2890, 57.4446, 59.4470, 59.6096, 59.8948, 60.0589, 62.7009, 62.8744, 68.4005, 73.2759 and 74.1075.

In the XRD pattern of Figure 34, the 2Θ peaks are located at angles 17.9999, 20.8402, 27.7064, 28.1354, 30.0268, 33.2742, 34.7830, 35.0720, 36.5637, 38.1282, 41.0802, 42.4897, 43.0029, 44.3998, 46.5320, 50.1146, 52.7430, 55.0726, 56.2351, 57.3247, 59.4893, 59.9469, 61.7002, 62.4732, 62.6866, 69.9849, 71.9636, 73.1842, 73.5804 and 74.1893.

Figure 35 illustrates a sectional scanning electron micrograph (SEM) of this material composition. This SEM shows the two phases, where the YSZ phase comprises the lighter, matrix phase, and the doped YAG phase comprises the darker, elongate or ribbon particles, which have an average length of less than about 200 μm in a direction parallel to the surface of the coating and an average thickness of less than about 5 μm in a direction orthogonal to the surface of the coating.

In this embodiment the YAG particles constitute splats which result from the impact of the molten YAG-based particles which are delivered by the plasma spraying apparatus and solidify rapidly into this form.

In this embodiment the YAG-based particles are substantially uniformly distributed throughout the coating. Example 5F

Figure 36 illustrates a sectional scanning electron micrograph (SEM) of this material composition. This SEM shows the two phases, where the YSZ phase comprises the lighter, matrix phase, and the doped YAG phase comprises the darker, elongate or ribbon particles, which have an average length of less than about 100 μm in a direction parallel to the surface of the coating and an average thickness of less than about 10 μm in a direction orthogonal to the surface of the coating.

In this embodiment the coating is a multi-layer coating which comprises a first, lower layer which comprises only the YSZ matrix phase, here having a thickness of less than about 250 μm, and a second, upper layer which comprises the YSZ matrix phase and the YAG-based particles distributed therewithin, here substantially uniformly, and having a thickness of less than about 150 μm. Example 5G

In this Example, a material composition is presented which comprises 80 wt% of a YSZ matrix phase and 20 wt% of a YAG-based second, luminescent phase which is doped with Tm in an amount of 0.5 mol% on the Y site.

Figure 37 illustrates a sectional scanning electron micrograph (SEM) of this material composition. This SEM shows the two phases, where the YSZ phase comprises the lighter, matrix phase, and the doped YAG phase comprises the darker, elongate or ribbon particles, which have an average length of less than about 150 μm in a direction parallel to the surface of the coating and an average thickness of less than about 20 μm in a direction orthogonal to the surface of the coating.

In this embodiment the coating is a multi-layer coating which comprises a first, lower layer which comprises only the YSZ matrix phase, here having a thickness of less than about 250 μm, and a second, upper layer which comprises the YSZ matrix phase and the YAG-based particles distributed therewithin, here substantially uniformly, and having a thickness of less than about 100 μm. The performance of the material compositions of this embodiment of the present invention is particularly surprising, insofar as the state of the art, as, for example, disclosed in Surface &. Coatings Technology 188-189 (2004), pages 93 to 100 (M. M. Gentleman et al), clearly envisages compositions based on a mixture of YSZ and YAG as being incompatible for applications in relation to TBCs.

Finally, it will be understood that the present invention has been described in its preferred embodiments and can be modified in many different ways without departing from the scope of the invention as defined by the appended claims.

Claims

1. A luminescent material composition comprising a first, matrix phase, a second phase within the matrix phase, and at least one luminescent dopant.

2. The composition of claim 1, wherein the matrix phase comprises a zirconia-based phase.

3. The composition of claim 2, wherein the zirconia-based matrix phase comprises yttria stabilized zirconia (YSZ).

4. The composition of claim 2, wherein the zirconia-based matrix phase comprises partially stabilized zirconia (PSZ).

5. The composition of claim 2, wherein the zirconia-based matrix phase comprises zirconia stabilized with from about 3 mol% to about 6 mol% yttria, and preferably 4 mol% yttria.

6. The composition of claim 2, wherein the zirconia-based matrix phase comprises zirconia stabilized with from about 6 mol% to about 10 mol% yttria, and preferably 8 mol% yttria.

7. The composition of any of claims 2 to 6, wherein the zirconia-based matrix phase includes at least one luminescent dopant.

8. The composition of claim 7, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

9. The composition of claim 8, wherein the lanthanide dopant comprises a single dopant selected from the elements Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

10. The composition of claim 8, wherein the lanthanide dopant comprises a pair of dopants selected from the pairs of elements Gd and Er, Gd and Nd, Gd and Yb, Yb and Nd and Yb and Sm.

11. The composition of claim 2, wherein the zirconia-based matrix phase comprises a zirconate pyrochlore (A₂Zr₂O₇), where A is preferably one or more elements selected from the lanthanide series.

12. The composition of claim 11, wherein A comprises one or more of the elements Gd, La, Nd and Sm.

13. The composition of any of claims 1 to 12, wherein the second phase contains Y and Al.

14. The composition of claim 13, wherein the second phase includes yttria and an aluminate.

15. The composition of claim 13, wherein the second phase comprises a YAG-based phase.

16. The composition of claim 15, wherein the YAG-based phase comprises Y₃AI₅O₁₂.

17. The composition of claim 15, wherein the YAG-based phase comprises Y₃AI_xFe_5-XOi₂, where X > 0.

18. The composition of any of claims 15 to 17, wherein the YAG-based phase includes at least one luminescent dopant.

19. The composition of claim 18, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

20. The composition of claim 19, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

21. The composition of any of claims 18 to 20, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

22. The composition of claim 21, wherein the at least one luminescent dopant is doped in an amount of between 0.5 mol% and 6 mol%.

23. The composition of claim 21, wherein the at least one luminescent dopant is doped in an amount of between 3 mol% and 6 mol%.

24. The composition of claim 21, wherein the at least one luminescent dopant is doped in an amount of between 4.5 mol% and 5.5 mol%.

25. The composition of claim 21, wherein the at least one luminescent dopant is doped in an amount of about 3 mol%.

26. The composition of claim 21, wherein the at least one luminescent dopant is doped in an amount of about 5 mol%.

27. The composition of claim 13, wherein the second phase comprises a YAP-based phase.

28. The composition of claim 27, wherein the YAP-based phase comprises YAIO₃.

29. The composition of claim 27 or 28, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

30. The composition of claim 29, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

31. The composition of any of claims 27 to 30, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

32. The composition of claim 31, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 3 mol%.

33. The composition of claim 31, wherein the at least one luminescent dopant is doped in an amount of about 0,3 mol%.

34. The composition of claim 31, wherein the at least one luminescent dopant is doped in an amount of about 1 mol%.

35. The composition of any of claims 1 to 12, wherein the second phase comprises a GdAIO₃-based phase.

36. The composition of claim 35, wherein the GdAIO₃-based phase comprises GdAIO₃.

37. The composition of claim 35 or 36, wherein the GdAIO₃-based phase includes at least one luminescent dopant.

38. The composition of claim 37, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

39. The composition of claim 38, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

40. The composition of any of claims 37 to 39, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

41. The composition of claim 40, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 3 mol%.

42. The composition of claim 40, wherein the at least one luminescent dopant is doped in an amount of about 0.3 mol%.

43. The composition of claim 40, wherein the at least one luminescent dopant is doped in an amount of about 1 mol%.

44. The composition of any of claims 1 to 12, wherein the second phase comprises an A₂B₂O₇ (pyrochlore) phase, where A comprises one or more elements selected from the lanthanide series or the actinide series and B comprises one or more elements selected from the group of transition metals.

45. The composition of claim 44, wherein A comprises one or more of the elements Gd, La, Nd and Sm.

46. The composition of claim 44 or 45, wherein B comprises the element Zr.

47. The composition of any of claims 44 to 46, wherein the pyrochlore phase includes at least one luminescent dopant.

48. The composition of claim 47, wherein the at least one luminescent dopant is selected from Pr and Tb.

49. The composition of claim 48, wherein the at least one luminescent dopant comprises Tb.

50. The composition of claim 48, wherein the at least one luminescent dopant comprises Pr.

51. The composition of claim 48, wherein the at least one luminescent dopant comprises Pr and Tb in combination.

52. The composition of any of claims 47 to 51, wherein the pyrochlore phase is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

53. The composition of claim 52, wherein the pyrochlore phase is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant.

54. The composition of claim 52, wherein the pyrochlore phase is doped with between 3 mol% and 7 mol% of the at least one luminescent dopant.

55. The composition of claim 52, wherein the pyrochlore phase is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

56. The composition of claim 52, wherein the pyrochlore phase is doped with about 5 mol% of the at least one luminescent dopant.

57. The composition of any of claims 1 to 12, wherein the second phase comprises an yttria-based phase.

58. The composition of claim 57, wherein the yttria-based phase comprises yttria.

59. The composition of any of claim 57 or 58, wherein the yttria-based phase includes at least one luminescent dopant.

60. The composition of claim 59, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

61. The composition of claim 60, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

62. The composition of any of claims 59 to 61, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

63. The composition of claim 62, wherein the at least one luminescent dopant is doped in an amount of between 0.5 mol% and 6 mol%.

64. The composition of claim 62, wherein the at least one luminescent dopant is doped in an amount of between 3 mol% and 6 mol%.

65. The composition of claim 62, wherein the at least one luminescent dopant is doped in an amount of between 4.5 mol% and 5.5 mol%.

66. The composition of claim 62, wherein the at least one luminescent dopant is doped in an amount of about 3 mol%.

67. The composition of claim 62, wherein the at least one luminescent dopant is doped in an amount of about 5 mol%.

68. The composition of any of claims 1 to 67, wherein the second phase comprises atomic clusters or particles.

69. The composition of claim 68, wherein the clusters or particles have a generally uniform shape.

70. The composition of claim 68 or 69, wherein the clusters or particles are of an average size of between 1 nm and 5 μm.

71. The composition of claim 70, wherein the clusters or particles are of an average size of between 1 nm and 2 μm.

72. The composition of claim 71, wherein the clusters or particles are of an average size of between 1 nm and 1 μm.

73. The composition of claim 72, wherein the clusters or particles are of an average size of between 1 nm and 100 nm.

74. The composition of claim 73, wherein the clusters or particles are of an average size of between 1 nm and 50 nm.

75. The composition of claim 74, wherein the clusters or particles are of an average size of between 20 nm and 50 nm.

76. The composition of claim 75, wherein the clusters or particles are of an average size of between 1 nm and 20 nm.

77. The composition of claim 76, wherein the clusters or particles are of an average size of between 1 nm and 10 nm.

78. The composition of claim 68, wherein the clusters or particles have an asymmetric shape.

79. The composition of claim 78, wherein the clusters or particles have an elongate or ribbon shape.

80. The composition of claim 79, wherein the clusters or particles have an average length of less than about 150 μm.

81. The composition of claim 80, wherein the clusters or particles have an average length of less than about 100 μm.

82. The composition of claim 81, wherein the clusters or particles have an average length of less than about 50 μm.

83. The composition of any of claims 79 to 82, wherein the clusters or particles have an average thickness of less than about 20 μm.

84. The composition of claim 83, wherein the clusters or particles have an average thickness of less than about 10 μm.

85. The composition of claim 84, wherein the clusters or particles have an average thickness of less than about 5 μm.

86. The composition of any of claims 1 to 85, where containing the second phase in an amount between 0.1 wt% and 20 wt%.

87. The composition of claim 86, where containing the second phase in an amount between 0.1 wt% and 10 wt%.

88. The composition of claim 87, where containing the second phase in an amount between 0.1 wt% and 5 wt%.

89. The composition of claim 88, where containing the second phase in an amount between 0.1 wt% and 2 wt%.

90. The composition of claim 89, where containing the second phase in an amount between 0.1 wt% and 1 wt%.

91. The composition of any of claims 1 to 90, wherein the second phase is a substantially crystalline phase.

92. The composition of any of claims 1 to 90, wherein the second phase is at least partially an amorphous phase.

93. The composition of claim 92, wherein the second phase is substantially an amorphous phase.

94. The composition of any of claims 1 to 93, wherein the second phase is a phase which is chemically and physically stable at temperatures of up to about 1700 C, and preferably when thermally cycled.

95. The composition of any of claims 1 to 94, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

96. The composition of claim 95, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

97. The composition of any of claims 1 to 96, where plasma sprayed from precursor powders of the first, matrix phase and the second phase.

98. The composition of any of claims 1 to 96, where formed by co- precipitation from a solution containing precursor materials in stoichiometric amounts.

99. A structure incorporating the luminescent material composition of any of claims 1 to 98.

100. The structure of claim 99, wherein the structure comprises a coating.

101. The structure of claim 100, wherein the structure comprises a multilayer coating, of which one layer comprises the luminescent material composition.

102. The structure of claim 101, wherein the coating comprises a first, lower layer which comprises substantially only the matrix phase, and a second, upper layer which comprises the matrix phase and the second phase distributed therewithin.

103. The structure of any of claims 100 to 102, wherein the coating is a solid, continuous coating.

104. The structure of any of claims 100 to 103, wherein the coating is a thermal barrier coating.

105. A structure comprising a main, structural phase, and a plurality of discrete, luminescent atomic clusters or particles which are distributed within the structural phase and act, when excited by an excitation signal, to emit a luminescence signal which is representative of one or more characteristics of the structure.

106. The structure of claim 105, wherein the structural phase is formed of a refractory material.

107. The structure of claim 105 or 106, wherein the structural phase comprises a zirconia-based phase.

108. The structure of claim 107, wherein the zirconia-based structural phase comprises yttria stabilized zirconia (YSZ).

109. The structure of claim 107, wherein the zirconia-based structural phase comprises partially stabilized zirconia (PSZ).

110. The structure of claim 107, wherein the zirconia-based structural phase comprises zirconia stabilized with from about 3 mol% to about 6 mol% yttria, and preferably 4 mol% yttria.

111. The structure of claim 107, wherein the zirconia-based structural phase comprises zirconia stabilized with from about 6 mol% to about 10 mol% yttria, and preferably 8 mol% yttria.

112. The structure of claim 107, wherein the zirconia-based structural phase comprises a zirconate pyrochlore (A₂Zr₂O₇), where A is preferably one or more elements selected from the lanthanide series.

113. The> structure of claim 112, wherein A comprises one or more of the elements Gd, La, Nd and Sm.

114. The structure of any of claims 105 to 113, wherein the luminescent clusters or particles are formed of a material composition which comprises a host phase which is doped with at least one luminescent dopant, which material composition provides a luminescent signal when excited with an excitation signal.

115. The structure of claim 114, wherein the host phase contains Y and Al.

116. The structure of claim 115, wherein the host phase includes yttria and an aluminate.

117. The structure of claim 115, wherein the host phase comprises a YAG- based phase.

118. The structure of claim 117, wherein the YAG-based phase comprises Y₃AI₅O₁₂.

119. The structure of claim 117, wherein the YAG-based phase comprises Y₃Al_xFe₅-χOi₂, where X > 0.

120. The structure of any of claims 117 to 119, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

121. The structure of claim 120, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

122. The structure of any of claims 117 to 121, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

123. The structure of claim 122, wherein the at least one luminescent dopant is doped in an amount of between 0.5 mol% and 6 mol%.

124. The structure of claim 122, wherein the at least one luminescent dopant is doped in an amount of between 3 mol% and 6 mol%.

125. The structure of claim 122, wherein the at least one luminescent dopant is doped in an amount of between 4.5 mol% and 5.5 mol%.

126. The structure of claim 122, wherein the at least one luminescent dopant is doped in an amount of about 3 mol%.

127. The structure of claim 122, wherein the at least one luminescent dopant is doped in an amount of about 5 mol%.

128. The structure of claim 115, wherein the host phase comprises a YAP- based phase.

129. The structure of claim 128, wherein the YAP-based phase comprises YAIO₃.

130. The structure of claim 128 or 129, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

131. The structure of claim 130, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

132. The structure of any of claims 128 to 131, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

133. The structure of claim 132, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 3 mol%.

134. The structure of claim 132, wherein the at least one luminescent dopant is doped in an amount of about 0.3 mol%.

135. The structure of claim 132, wherein the at least one luminescent dopant is doped in an amount of about 1 mol%.

136. The structure of claim 114, wherein the host phase comprises a GdAIO₃-based phase.

137. The structure of claim 136, wherein the GdAIO₃-based phase comprises GdAIO₃.

138. The structure of claim 136 or 137, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

139. The structure of claim 138, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

140. The structure of any of claims 136 to 139, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

141. The structure of claim 140, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 3 mol%.

142. The structure of claim 140, wherein the at least one luminescent dopant is doped in an amount of about 0.3 mol%.

143. The structure of claim 140, wherein the at least one luminescent dopant is doped in an amount of about 1 mol%.

144. The structure of claim 114, wherein the host phase comprises an A₂B₂O₇ (pyrochlore) phase, where A comprises one or more elements selected from the lanthanide series or the actinide series and B comprises one or more elements selected from the group of transition metals.

145. The structure of claim 144, wherein A comprises one or more of the elements Gd, La, Nd and Sm.

146. The structure of claim 144 or 145, wherein B comprises the element Zr.

147. The structure of any of claims 144 to 146, wherein the at least one luminescent dopant is selected from Pr and Tb.

148. The structure of claim 147, wherein the at least one luminescent dopant comprises Tb.

149. The structure of claim 147, wherein the at least one luminescent dopant comprises Pr.

150. The structure of claim 147, wherein the at least one luminescent dopant comprises Pr and Tb in combination.

151. The structure of any of claims 144 to 150, wherein the pyrochlore phase is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

152. The structure of claim 151, wherein the pyrochlore phase is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant.

153. The structure of claim 151, wherein the pyrochlore phase is doped with between 3 mol% and 7 mol% of the at least one luminescent dopant.

154. The structure of claim 151, wherein the pyrochlore phase is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

155. The structure of claim 151, wherein the pyrochlore phase is doped with about 5 mol% of the at least one luminescent dopant.

156. The structure of claim 114, wherein the host phase comprises an yttria-based phase.

157. The structure of claim 156, wherein the yttria-based phase comprises yttria.

158. The structure of claim 156 or 157, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

159. The structure of claim 158, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

160. The structure of any of claims 156 to 159, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

161. The structure of claim 160, wherein the at least one luminescent dopant is doped in an amount of between 0.5 mol% and 6 mol%.

162. The structure of claim 160, wherein the at least one luminescent dopant is doped in an amount of between 3 mol% and 6 mol%.

163. The structure of claim 160, wherein the at least one luminescent dopant is doped in an amount of between 4.5 mol% and 5.5 mol%.

164. The structure of claim 160, wherein the at least one luminescent dopant is doped in an amount of about 3 mol%.

165. The structure of claim 160, wherein the at least one luminescent dopant is doped in an amount of about 5 mol%.

166. The structure of any of claims 105 to 165, wherein the clusters or particles have a generally uniform shape.

167. The structure of claim 166, wherein the clusters or particles are of an average size of between 1 nm and 5 μm.

168. The structure of claim 167, wherein the clusters or particles are of an average size of between 1 nm and 2 μm.

169. The structure of claim 168, wherein the clusters or particles are of an average size of between 1 nm and 1 μm.

170. The structure of claim 169, wherein the clusters or particles are of an average size of between 1 nm and 100 nm.

171. The structure of claim 170, wherein the clusters or particles are of an average size of between 1 nm and 50 nm.

172. The structure of claim 171, wherein the clusters or particles are of an average size of between 20 nm and 50 nm.

173. The structure of claim 171, wherein the clusters or particles are of an average size of between 1 nm and 20 nm.

174. The structure of claim 173, wherein the clusters or particles are of an average size between 1 nm and 10 nm.

175. The structure of ay of claims 105 to 165, wherein the clusters or particles have an asymmetric shape.

176. The structure of claim 175, wherein the clusters or particles have an elongate or ribbon shape.

177. The structure of claim 176, wherein the clusters or particles have an average length of less than about 150 μm.

178. The structure of claim 177, wherein the clusters or particles have an average length of less than about 100 μm.

179. The structure of claim 178, wherein the clusters or particles have an average length of less than about 50 μm.

180. The structure of any of claims 176 to 179, wherein the clusters or particles have an average thickness of less than about 20 μm.

181. The structure of claim 180, wherein the clusters or particles have an average thickness of less than about 10 μm.

182. The structure of claim 181, wherein the clusters or particles have an average thickness of less than about 5 μm.

183. The structure of any of claims 105 to 182, where containing the luminescent clusters or particles in an amount between 0.1 wt% and 20 wt%.

184. The structure of claim 183, where containing the luminescent clusters or particles in an amount between 0.1 wt% and 10 wt%.

185. The structure of claim 184, where containing the luminescent clusters or particles in an amount between 0.1 wt% and 5 wt%.

186. The structure of claim 185, where containing the luminescent clusters or particles in an amount between 0.1 wt% and 2 wt%.

187. The structure of claim 186, where containing the luminescent clusters or particles in an amount between 0.1 wt% and 1 wt%.

188. The structure of any of claims 105 to 187, wherein the luminescent clusters or particles comprise a substantially crystalline phase.

189. The structure of any of claims 105 to 187, wherein the luminescent clusters or particles comprise at least partially an amorphous phase.

190. The structure of claim 189, wherein the luminescent clusters or particles comprise an amorphous phase.

191. The structure of any of claims 105 to 190, wherein the luminescent clusters or particles are formed of a phase which is chemically and physically stable at temperatures of up to about 1700 C, and preferably when thermally cycled.

192. The structure of any of claims 105 to 191, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

193. The structure of claim 192, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

194. The structure of any of claims 105 to 193, where plasma sprayed from precursor powders of the structural phase and the luminescent clusters or particles.

195. The structure of any of claims 105 to 193, where formed by co- precipitation from a solution containing precursor materials in stoichiometric amounts.

196. The structure of claim 194 or 195, where formed as a coating on an object.

197. The structure of claim 196, wherein the coating is a TBC.

198. The structure of claim 196 or 197, wherein the structure comprises a multi-layer coating, one layer of which includes the luminescent clusters or particles.

199. The structure of claim 198, wherein the coating comprises a first, lower layer which comprises substantially only the structural phase, and a second, upper layer which comprises the structural phase and the luminescent clusters or particles distributed therewithin.

200. The structure of any of claims 196 to 199, wherein the coating is a solid, continuous coating.

201. The structure of any of claims 105 to 200, wherein the luminescent clusters or particles comprise a phase which is chemically and physically stable at temperatures of up to about 1700 C, and preferably when thermally cycled.

202. The structure of any of claims 105 to 201, wherein the luminescent clusters or particles are clusters or particles which are able to co-exist in the structural phase, preferably at temperatures exceeding 1000 C.

203. The structure of any of claims 105 to 202, wherein the size and distribution of the luminescent clusters or particles is such as not significantly to alter the physical or chemical characteristics of the structural phase, but yet sufficient to provide a luminescence signal.

204. A luminescent material composition comprising a YAG-based host phase and at least one luminescent dopant.

205. The composition of claim 204, wherein the YAG-based host phase comprises Y₃AI₅Oi₂.

206. The composition of claim 204, wherein the YAG-based host phase comprises YsAI_xFe_5-XO₁₂, where X > 0.

207. The composition of any of claims 204 to 206, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

208. The composition of claim 207, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

209. The composition of any of claims 204 to 208, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

210. The composition of claim 209, wherein the at least one luminescent dopant is doped in an amount of between 0.5 mol% and 6 mol%.

211. The composition of claim 209, wherein the at least one luminescent dopant is doped in an amount of between 3 mol% and 6 mol%.

212. The composition of claim 209, wherein the at least one luminescent dopant is doped in an amount of between 4.5 mol% and 5.5 mol%.

213. The composition of claim 209, wherein the at least one luminescent dopant is doped in an amount of about 3 mol%.

214. The composition of claim 209, wherein the at least one luminescent dopant is doped in an amount of about 5 mol%.

215. A structure incorporating the luminescent material composition of any of claims 204 to 214.

216. The structure of claim 215, wherein the structure comprises a coating.

217. The structure of claim 216, wherein the structure comprises a multilayer coating, of which one layer comprises the luminescent material composition.

218. The structure of claim 216 or 217, wherein the coating is a thermal barrier coating.

219. A luminescent material composition comprising a YAP-based host phase and at least one luminescent dopant.

220. The composition of claim 219, wherein the YAP-based host phase comprises YAIO₃.

221. The composition of claim 219 or 220, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

222. The composition of claim 221, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

223. The composition of any of claims 219 to 222, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

224. The composition of claim 223, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 3 mol%.

225. The composition of claim 223, wherein the at least one luminescent dopant is doped in an amount of about 0.3 mol%.

226. The composition of claim 223, wherein the at least one luminescent dopant is doped in an amount of about 1 mol%.

227. A structure incorporating the luminescent material composition of any of claims 219 to 226.

228. The structure of claim 227, wherein the structure comprises a coating.

229. The structure of claim 228, wherein the structure comprises a multilayer coating, of which one layer comprises the luminescent material composition.

230. The structure of claim 228 or 229, wherein the coating is a thermal barrier coating.

231. A luminescent material composition comprising a GdAIO₃-based host phase and at least one luminescent dopant.

232. The composition of claim 231, wherein the GdAIO₃-based host phase comprises GdAIO₃.

233. The composition of claim 231 or 232, wherein the at least one luminescent dopant comprises one or more elements selected from the lanthanide series.

234. The composition of claim 233, wherein the at least one luminescent dopant comprises one or more elements selected from Ce, Dy, Er, Eu, Gd, Ho, Nd, Pr, Sm, Tb, Tm and Yb.

235. The composition of any of claims 231 to 234, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 6 mol%.

236. The composition of claim 235, wherein the at least one luminescent dopant is doped in an amount of between 0.1 mol% and 3 mol%.

237. The composition of claim 235, wherein the at least one luminescent dopant is doped in an amount of about 0.3 mol%.

238. The composition of claim 235, wherein the at least one luminescent dopant is doped in an amount of about 1 mol%.

239. A structure incorporating the luminescent material composition of any of claims 231 to 238.

240. The structure of claim 239, wherein the structure comprises a coating.

241. The structure of claim 240, wherein the structure comprises a multilayer coating, of which one layer comprises the luminescent material composition.

242. The structure of claim 240 or 241, wherein the coating is a thermal barrier coating.

243. A luminescent material composition which comprises an A₂B₂O₇ (pyrochlore) host phase which is doped with at least one luminescent dopant, where A comprises one or more elements selected from the lanthanide series or the actinide series and B comprises one or more elements selected from the group of transition metals.

244. The composition of claim 243, wherein the at least one luminescent dopant is selected from Pr and Tb.

245. The composition of claim 244, wherein the at least one luminescent dopant comprises Tb.

246. The composition of claim 244, wherein the at least one luminescent dopant comprises Pr.

247. The composition of claim 244, wherein the at least one luminescent dopant comprises Pr and Tb in combination.

248. The composition of any of claims 243 to 247, wherein the host phase is doped with between 1 mol% and 10 mol% of the at least one luminescent dopant.

249. The composition of claim 248, wherein the host phase is doped with between 1 mol% and 7 mol% of the at least one luminescent dopant.

250. The composition of claim 248, wherein the host phase is doped with between 3 mol% and 7 mol% of the at least one luminescent dopant.

251. The composition of claim 248, wherein the host phase is doped with between 4 mol% and 6 mol% of the at least one luminescent dopant.

252. The composition of claim 248, wherein the host phase is doped with about 5 mol% of the at least one luminescent dopant.

253. A structure incorporating the luminescent material composition of any of claims 243 to 252.

254. The structure of claim 253, wherein the structure comprises a coating.

255. The structure of claim 254, wherein the structure comprises a multilayer coating, of which one layer comprises the luminescent material composition.

256. The structure of claim 254 or 255, wherein the coating is a thermal barrier coating.