GB2437729A

GB2437729A - Ultraviolet excited white phosphor and light emitting devices thereof

Info

Publication number: GB2437729A
Application number: GB0608905A
Authority: GB
Inventors: Elmar C Fuchs; Karl Gatterer
Original assignee: Technische Universitaet Graz
Current assignee: Technische Universitaet Graz
Priority date: 2006-05-05
Filing date: 2006-05-05
Publication date: 2007-11-07
Also published as: WO2007128016A2; WO2007128016A3; GB0608905D0

Abstract

An ultraviolet-excited phosphor is composed of a dysprosium and thulium-activated rare-earth aluminum, scandium borate that is represented by a general formula (Y1-x-yTmxDyy)Al3-zScz(BO3)4 (where 0 < (x+y) & 1, 0 & z & 3). This phosphor, when irradiated by ultraviolet light having a wavelength of 350 nm or less, can produce white light having composed of the wavelengths 451, 455, 470, 474, 481, 485, 564, 567, 571, 574, 579 and several peaks in the range of Ò5 nm around these wavelengths with higher efficiency and stronger emitted intensity, having a colour temperature of approximately 4600 - 10000 K.

Description

Field of the Invention

The present invention relates to an ultraviolet-excited white phosphor and to light-emitting devices that use this phosphor.

Description of the Related Art

Human beings interpret quite different visual stimuli as the colour "white". Not only broad band emissions like the ones from daylight sources produce a "white" perception, but also narrow band light sources like fluorescent tubes. These are glass tubes filled with mercury vapour and electrodes at each end. The interior of the tube is coated with a fluorescent material consisting of a phosphor. This material absorbs most of the UV -part of the Hg emission and show broad band luminescence mainly in the red part of the visible spectrum. The white light produced in fluorescent tubes is a combination of the visible emission of mercury at 368, 408 and 439 nm and the luminescence of the coating.

In recent years, there is a growing concern about the mercury which eventually pollutes the environment because it is a health hazard. Therefore, there is an increasing demand for light emitting devices that are operated without mercury.

White light fluorescent tubes that are operated without mercury therefore demand a phosphor that has a great light-emitting intensity and can deliver white light at high efficiency directly from UV-excitation of the phosphor in the coating..

It is well known that rare earth ions which are doped into solid host materials can give rise to sharp emissions in the visible spectrum. For example, Eu3:Y2O3 is one of the most efficient red phosphors. . Other rare earth ions have their emissions at different wavelengths. : Yttrium aluminium borate (YAB) and Yttrium aluminium scandium borate are suitable hosts for rare-earth ions. YAB forms uniaxial crystals of huntite type in space group R32 with three formula units per unit cell. It consists of a layered arrangement of alternating B033-triangles and metal ion layers along the <001> direction, which coincides with the crystallographic c-axis. The Y3 ions are located in trigonal prismatic sites with D3 symmetry. They are co-ordinated to three oxygens from the. : borate top and bottom layers, respectively, where the two oxygen triangles are slightly rotated (8.3 ) against each other. Upon doping, the rare earth ions replace yttrium ions. * In the quest for a material which shows rare earth emission in the visible range such that this emission stimulates a white colour perception we have produced dozens of doped YAB crystals containing *.

different combinations and amounts of rare earth ions.

Among these many samples those systems which contained Tm3 and Dy3 simultaneously in the proper ratio were the only ones showing the desired effect. It should be emphasised that the white impression results from luminescence of the rare earth ions only and does not require the presence of mercury emission bands.

Summary of the Invention

It is the object of the present invention to provide an ultraviolet-excited white phosphor having strong light-emitting intensity that can deliver white light with high efficiency.

Accordingly, the ultraviolet-excited phosphor of the present invention is composed of a thulium and dysprosium activated rare-earth aluminum-scandium borate that is represented by the general formula (where 0 < (x+y) = 1, 0 = z = 3).

A white luminescent fluorescent lamp can be provided in which excitation by ultraviolet light that is radiated by a discharge medium causes efficient emission within the visible wavelength range of 451 nm -579 nm which is interpreted as white light by the human eye.

Further, the discharge medium may be a noble gas, the noble gas, e.g., may be xenon gas.

The features mentioned above will become evident from the following description with reference to the figures which illustrate examples of the present invention.

Brief Description of the Drawings

FIG. 1 is a graph showing a comparison of the relationship between the emitted intensities of the phosphors and the corresponding colour temperature according to each working example of the present invention.

FIG. 2 is a graph showing the x,y co-ordinates in the 1931 x,y colour space of the working examples 1-5 of the present invention.

Detailed Description of the Invention

As described above, as a result of continued research and development, the inventors of the present invention have succeeded in discovering a material with superior light-emission characteristics of light perceived as white by the human eye, an ultraviolet-excited phosphor that is composed of thulium and dysprosium activated rare-earth aluminum-scandium borate that is represented by the general formula (where 0 < (x+y) = 1, 0 = z = 3).

In regard to the method of producing the ultraviolet-excited phosphor of the present invention, an * yttrium compound such as yttrium oxide, a thulium compound such as thulium oxide, a dysprosium: compound such as dysprosium oxide, an aluminum compound such as aluminum oxide, a scandium *.

compound such as scandium oxide, and a boron compound such as boron oxide are first taken as the basic materials of this phosphor. These basic materials are next weighed, collected, and well mixed in accordance with the above-described compositional formula.

These materials are next poured into a heat-resistant receptacle such as a crucible that is composed of * : alumina, carbon, or platinum, and undergo pre-sintering at a temperature of 400-600 C. The materials next undergo sintering for 3-20 hours in air at a temperature of 900-1200 C, and the obtained sintered material is next subjected to pulverization, washing, drying, and sorting to obtain the ultraviolet-excited white phosphor of the present invention in powdered form. : The above-described pre-sintering and main sintering may be carried out in an oxidizing atmosphere.

Further, the phosphor that has been obtained as described above may again undergo sintenng and then similarly undergo the processes of pulverization, washing, drying and sorting to obtain the ultraviolet-excited phosphor.

Alternatively, the materials are mixed with an excess of a high temperature flux such as an arbitrary mixture of K2S04 and MoO3, then poured into a heat-resistant receptacle such as a crucible that is composed of alumina, carbon, or platinum, and undergo pre-sintering at a temperature of 400-600 C.

The materials next undergo main melting for 2 hours in air at a temperature of 1120 C and are then cooled down at the rate of 1 C / hour to 850 C. The material is next subjected to washing with a strong base such as KOH 8m, and the crystals obtained are then being washed, dried and sorted to obtain the ultraviolet-excited phosphor of the present invention in single crystalline form.

An actual example of the ultraviolet-excited white phosphor of the present invention is next described with reference to the following working examples.

Working Example 1

As the raw materials of the phosphor, 1.5968 g of Y203, 0.2296 g of Dy203, 0.0030 g of Tm203, 2.3537 g of A1203, 2.1441 g of B203, 3.50 g of K2S04, 9.64g of MoO3 are each weighed, and following uniform mixing, are poured into a crucible made of alumina and subjected to pre-sintering for two hours at 500 C in air. The temperature is raised to 1120 C, and after heating for two hours in air, the material undergoes slow cooling with a rate of 1 C / hour to obtain crystals of the material in the molten flux. The material next undergoes boiling in KOH, 8m, and the obtained crystals undergo a cleaning, drying, and sorting processes to obtain the ultraviolet-excited white phosphor according to Working Example 1 having a composition of YO.919DyOO8OTmO.OOIA13(B03)4.

Working Examples 2-5

The ratios among the Y component, Tm component, Al component and Dy component were modified as appropriate and the processes of, for example, mixing and sintering and crystal growing were carried out under the same conditions as in the Working Example 1 to obtain ultraviolet-excited white phosphors having the compositions as shown in Table 1 below: Yo.93Dy0.04Tm0.03A13(B03)4 (Working Example 2), Yo.91Dyo.o4Tmo.05A13(B03)4 (Working Example 3), Yo89Tmo.o4Dyo.07A13(B03)4 (Working Example 4), Yo.giDyo.o4Tmo.09A13(B03)4

(Working Example 5),

FIG. 1 is a graph showing a comparison of the relationship between the emitted wavelengths of phosphors by means of its colour temperature according to each working example of the present invention. : FIG. 2 is a graph showing the x,y co-ordinates in the 1931 x,y colour space of the working example1* *.

1-5 of the present invention.

Thus, an ultraviolet-excited white phosphor according to the present invention has a strong emitted intensity and can supply white light at high efficiency, and therefore can be applied to various types of * : light-emitting devices that take a noble gas such as xenon as the excitation source. *.*S * * SI.,

* I. I p 5 5 ** S

Claims

Claims 1. An ultraviolet-excited phosphor containing a dysprosium and

thulium-activated rare-earth aluminum-scandium borate [general formula (where 0 < (x+y) = 1, 0 = z =3)].

2. An ultraviolet-excited phosphor containing a dysprosium and thulium-activated rare-earth aluminum borate [general formula (YiTmDy)Al3(BO3)4 (where 0 < (x+y) = 1)].

3. An ultraviolet-excited phosphor containing a dysprosium and thulium-activated rare-earth aluminum borate [general formula (Y1.TmDy)Al3(BO3)4 (where 0,03 <x <0,05; 0,03 <y <0,05) which converts UV light to white light close to the white-point in the CIE 1931 x,y chromaticity diagram.

4. An ultraviolet-excited phosphor containing a dysprosium and thulium-activated rare-earth aluminum-scandium borate [general formula (where 0,03 <x <0,05; 0,03 <y <0,05; 0 = z = 3) which converts UV light to white light close to the chromaticity coordinate of the colour white in the CIE 1931 x,y chromaticity diagram.

5. Any white luminescent fluorescent lamp containing the material described in claims 1-4.

* .)** 6. Any light emitting device containing the material described in claims 1-4.

7. Any plasma display panel, wherein the used phosphor contains the material described in claims 1-4. .. * * . . *1 * b* * I. S * S S. *