WO2003087441A1 - Luminophores photoniques et dispositifs - Google Patents

Luminophores photoniques et dispositifs Download PDF

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Publication number
WO2003087441A1
WO2003087441A1 PCT/GB2003/001486 GB0301486W WO03087441A1 WO 2003087441 A1 WO2003087441 A1 WO 2003087441A1 GB 0301486 W GB0301486 W GB 0301486W WO 03087441 A1 WO03087441 A1 WO 03087441A1
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Prior art keywords
phosphor
memory device
structured material
structured
photonic
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PCT/GB2003/001486
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English (en)
Inventor
Jack Silver
Robert Withnall
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Btg International Limited
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Priority to AU2003226534A priority Critical patent/AU2003226534A1/en
Publication of WO2003087441A1 publication Critical patent/WO2003087441A1/fr

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/244—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only
    • G11B7/245—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising organic materials only containing a polymeric component
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/02—Use of particular materials as binders, particle coatings or suspension media therefor
    • C09K11/025—Use of particular materials as binders, particle coatings or suspension media therefor non-luminescent particle coatings or suspension media
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7701—Chalogenides
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K11/00—Luminescent, e.g. electroluminescent, chemiluminescent materials
    • C09K11/08—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials
    • C09K11/77—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals
    • C09K11/7728—Luminescent, e.g. electroluminescent, chemiluminescent materials containing inorganic luminescent materials containing rare earth metals containing europium
    • C09K11/7729—Chalcogenides
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/60—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape characterised by shape
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B5/00—Single-crystal growth from gels
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1225—Basic optical elements, e.g. light-guiding paths comprising photonic band-gap structures or photonic lattices
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24302—Metals or metalloids
    • G11B2007/24314—Metals or metalloids group 15 elements (e.g. Sb, Bi)
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B2007/24318—Non-metallic elements
    • G11B2007/2432—Oxygen
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0045—Recording
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/005—Reproducing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/242—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers
    • G11B7/243—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of recording layers comprising inorganic materials only, e.g. ablative layers
    • G11B7/2433—Metals or elements of Groups 13, 14, 15 or 16 of the Periodic Table, e.g. B, Si, Ge, As, Sb, Bi, Se or Te
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/24—Record carriers characterised by shape, structure or physical properties, or by the selection of the material
    • G11B7/241—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material
    • G11B7/252—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers
    • G11B7/258—Record carriers characterised by shape, structure or physical properties, or by the selection of the material characterised by the selection of the material of layers other than recording layers of reflective layers

Definitions

  • the present invention relates to photonic materials and devices .
  • Photonic structures are usually periodic.
  • the periodicity of the lattice being on a length scale similar to that of the wavelength of the light transmitted or rejected.
  • Such a lattice manifests a refractive index contrast.
  • the lattice will have a photonic bandgap (named by analogy with the bandgap in electronic states in solids) if the contrast is high enough.
  • the position of the photonic bandgap can be controlled by varying the interplanar photonic lattice spacing.
  • Optical properties for example the transmission spectrum, depend on the structures rather than just the optical properties of the materials from which they are constructed.
  • Photonic structures have various applications, including waveguides and filters.
  • Luminescence is the emission of light from a material that has been excited. Luminescence is distinguished from incandescence, which is the emission of light by hot materials, but nevertheless luminescence can take place over a wide range of temperatures.
  • the exciting energy for luminescence can be provided by, for example, light, or other photons, electric current passing through the material, bombarding the material with electrons, chemical or biochemical reactions, friction (triboluminescence) , shock or sound, or even heat (thermoluminescence) .
  • Luminescence can be classified into phosphorescence, where emission continues for an extended period after excitation (sometimes seconds or minutes) , and fluorescence, where emission decays rapidly on a sub-microsecond timescale once the excitation is removed. Materials which exhibit useful luminescence properties, whether they phosphoresce or fluoresce, are termed phosphors, both herein, and generally in the art. Phosphors have many uses including lighting and displays.
  • photoluminescent phosphor Two important classes of photoluminescent phosphor are Stokes phosphors, where the emitted light is of longer wavelength than the absorbed and anti-Stokes phosphors, which emit a light of a shorter wavelength than that absorbed.
  • the present invention utilises a combination of phosphors and photonic structures. Further, as explained below, such new materials have interesting and useful properties, and these properties can be used in new optical devices incorporating the materials.
  • FIGURE 1 is a cross section of a photonic phosphor lattice according to the invention.
  • FIGURE 2 is a simplified model energy level diagram for a phosphor atom/molecule/ion exhibiting anti-Stokes behaviour.
  • FIGURE 3a is a cross section of a phosphor clad in a photonic lattice according to the invention.
  • FIGURE 3b is a cross section of one and two dimensional photonic phosphor lattices according to the present invention.
  • FIGURE 4 shows an example of a memory device according to the present invention.
  • FIGURE 5 is a simplified model energy level diagram for a phosphor atom/molecule/ion illustrating reading from the device .
  • FIGURE is a simplified model energy level diagram for a phosphor atom/molecule/ion illustrating an alternative read/write method for the memory device .
  • FIGURE shows a high efficiency phosphor according to the present invention.
  • FIGURE is a simplified model energy level diagram for a phosphor atom/molecule/ion illustrating the operation of the high efficiency phosphor of Figure 7.
  • FIGURE is an S.E.M. of a two dimensional lattice of
  • FIGURE 10 is an anti-Stokes luminescence spectrum under
  • FIGURE 11 is S.E.M. image of a three dimensional lattice of Zr0 2 :Eu 3+ .
  • FIGURE 12 is T.E.M. images of a three dimensional lattice of Zr0 2 :Eu 3+ at a magnification of (a)
  • FIGURE 13 is an anti-Stokes luminescence spectrum from the Zr0 2 :Eu 3+ lattice (shown in Figure 12) as a function of the angle of incidence of the
  • FIGURE 14 is a Stokes luminescence spectrum from the Zr0 2 :Eu 3+ lattice (shown in Figure 12) as a function of the angle of incidence of the 514.5 nm exciting light.
  • FIGURE 15 is an S.E.M. image of an inverse periodic air/Ti0 2 :Er 3+ lattice at x 25,800 magnification.
  • FIGURE 16 shows Raman and luminescence spectra of the inverse periodic air/Ti0 2 :Er 3+ (solid line) and bulk Ti0 2 :Er 3+ (dotted line), (a) in the anti-Stokes region and (b) in the Stokes region.
  • the exciting wavelength was equal to 632.8 nm.
  • a photonic structure comprises a face centred cubic (FCC) lattice of spheres 1 of air separated by solid phosphor 2, made of Zr0 2 :Eu 3+ , occupying the spaces between those spheres.
  • Zr0 2 :Eu 3+ denotes zirconia doped with europium in its 3+ (cation) state.
  • the relative rates of the electronic decay pathways are modified by the photonic lattice resulting in an extended excited state lifetime.
  • the preferred concentration of the europium (Er) is concentration of up to 5 atomic%. Further examples of materials according to the invention and of how they are made are described later.
  • Figure 2 is an energy level diagram of a simplified model atom exhibiting anti-Stokes behaviour.
  • the atom in its ground state E 0 absorbs a first photon 5 and is promoted to a first excited state Ei; a second photon 6 is absorbed sequentially or simultaneously and the atom is promoted to a higher energy second excited state E 2 .
  • this state is not stable and the atom emits (either spontaneously or otherwise) a higher energy photon 7 and returns to its ground state.
  • the gaps in energy E ⁇ -E 0 and E 2 -E ⁇ have been shown as equal they can be of different sizes - the uses that can be made of similar and different sized gaps are noted below.
  • the material used in the example of Figure 1 has strong anti-Stokes behaviour under excitation by red light of lower energy than the emission.
  • the photonic structure is so arranged (in particular by choosing the size of the spheres and hence the lattice parameter of the FCC lattice) that the material has a photonic bandgap, or stop-band, at the frequency of the photon that would be emitted by Eu 3+ (in Zr0 2 :Eu 3+ ) from its anti-Stokes emitting excited state (i.e. the one like E 2 in the model atom Figure 2) .
  • the photonic bandgap inhibits the production of these photons and hence stabilises this excited state.
  • the excited state lasts for up to 100 times longer than without the photonic lattice. (In Zr0 2 :Eu 3+ without the photonic lattice the relevant excited state lasts for the order of microseconds . ) Note that although the phosphor is embedded in the high refractive index material, this is not essential; the phosphor could equally be embedded in the low index material and still be subject to effect of the photonic bandgap of the structure . Further the absolute magnitudes of the refractive indices are not what is important, to the photonic bandgap effects, but rather the difference between them.
  • FIG 3a shows an alternative material according to the present invention.
  • the phosphor was embedded in the photonic structure.
  • a phosphor material 10 e.g. zirconia doped with europium Zr0 2 :Eu 3+
  • a surrounding layer having a photonic structure 11 e.g. air/undoped zirconia Zr0 2
  • the excited state is stabilised in that a first phosphor ion (Eu 3+ ) in the excited state will emit a photon 12 (of energy E 2 -E 0 in the model of Figure 2) , which will be absorbed by another phosphor ion, which is promoted to the same excited state thereby maintaining the population in that state.
  • the bandgap of the photonic structure 11 is arranged to prevent such photons from entering the photonic structure layer, which reflects them back into the phosphor material 10.
  • the bandgap is controlled as before - by choosing the size of the photonic lattice spacing and the materials (for their refractive indices) .
  • zirconia is a component of both the phosphor material and the photonic cladding. This is not essential but may be convenient.
  • Figure 3b is a cross section of a two-dimensional photonic lattice 13 with embedded phosphor having a photoemission mode suppressed by its bandgap.
  • This lattice has substantial extent in the dimensions across the page and into / out of the page and provides a photonic bandgap in those directions which suppresses the said photoemission mode. It is, however, only a few repeat units deep in the perpendicular dimension (i.e.
  • Reflective material 14 is provided, however, on both sides of the lattice to reflect back into it photons of said photoemission mode, which are then reabsorbed and are thus confined. Light of other wavelengths can be transmitted into and out of the lattice via the edges of the lattice not covered by the reflective material.
  • a similar arrangement for which Figure 3b is also the cross section, is one-dimensional photonic lattice with embedded phosphor having a photoemission mode suppressed by its bandgap.
  • the photonic bandgap exists only in the direction across the page and reflective material is placed to confine emitted light in the other two dimensions.
  • Figure 4 shows an example of a memory device according to the present invention, which utilises the properties of a photonic lattice.
  • An element 15 of memory material is a photonic structure having embedded anti-Stokes phosphor that has an emitting state stabilised by the photonic stop-band.
  • An input light guide 16 carries light, preferably in the form of pulses, which excite the phosphor of the memory material to its stabilised state. Information can be recorded because it can be chosen whether or not to excite the material with the input light.
  • the preferred method of reading the stored information is illustrated by the energy level diagram of Figure 5.
  • This shows the same energy levels as Figure 2 but also shows a fourth, higher level E 3 .
  • the memory material is irradiated 25, via light guide 16 with light at the frequency (E 3 -E 2 ) /h - where h is Plank's constant - to further promote phosphor atoms in the stabilised state (E 2 ) to energy level E 3 .
  • this frequency is outside the photonic bandgap so that a substantial flux will be conducted into the memory material.
  • the atom will emit a high-energy photon 26 of a frequency above the forbidden range of photonic bandgap. This transition may be back to the ground state E 0 , but other transitions are possible.
  • an output pulse of light of the relevant frequency will result, which is collected, at least in part by an output light guide 17.
  • the memory device phosphor 15 was in its ground state (because it was not written to) no output pulse will result.
  • the output pulse, or lack of it, can then be received by an optoelectronic sensor or used as an input to some other photonic device .
  • a filter 18 in light guide 17 may be used to ensure that only light of the output frequency is conveyed to the next device.
  • the output pulse will be of low intensity.
  • the memory material is shaped, being provided with facets 19, so as to reflect output photons into the output guide 17.
  • the memory device of Figure 4 is excited into its stabilised state by two photons.
  • these are of the same (or sufficiently similar) frequency, as shown in Figures 2 and 5 , and are provided by the same input pulse of light.
  • the energy levels are not, however, evenly spaced (i.e. E 2 -E ⁇ ⁇ E ⁇ -E 0 ) in which case it may be necessary to provide photons of two different wavelengths to achieve the excitation to the stabilised state.
  • excitation can be by simultaneous or sequential application of pulses of the relevant wavelength. Alternatively one of those wavelengths can be supplied continuously with the other being supplied as a pulse when it is desired to write to the memory device.
  • excitation is to a state E 2 by a wavelength 30 shorter than that of the photonic bandgap.
  • This state rapidly decays to a state Ei, other than the ground state (by the emission of a photon 31 or in some other way e.g. one or more phonons) .
  • the state E x is arranged to be stabilised by the photonic structure and so records the information written to the device.
  • the atom is excited with another photon 32 to a state E 3 , which then decays emitting a photon 33, which is not excluded by the photonic structure.
  • no output pulse is produced and thus the information written to the device is reproduced in the output.
  • the state to which excitation is made for reading is preferably not the same state as the state E 2 to which excitation is initially made for writing.
  • the reason is that if the transition E 2 to Ej. is selected to be a preferred transition of the atom, for efficiency of writing, then promoting the atom again to E 2 on reading will more likely result in the atom returning to Ei than emitting a higher energy photon outside the photonic bandgap which would provide the output signal of the device .
  • co-activator In phosphor technology it is known to include in the material in addition to the phosphorescent centre a co- activator, or sensitiser.
  • the function of a co-activator is to absorb energy and then pass it on, via a photon or otherwise, to excite the phosphorescent centre.
  • Use of co-activators is within the scope of the present invention.
  • the number of light guides attached to the memory device can vary in number. As noted above various input wavelength continuous beams or pulses may be required to write to and read from the device. In general different input beams (or pulses) may share the same light guide, or there may be provided one or more additional guides, as indicated with a dashed line at 21 in Figure 4) , that can conduct one, or as desired more, of those beams.
  • Input and output light guides are convenient ways of conducting light into and away from the device. Other arrangements are possible. Input and output beams can be arranged to propagate through free space .
  • the shaped facets are not essential, but on the other hand, coating with metal to form a mirror would increase the efficiency of the facets.
  • This optical memory device provided by the present invention could be used as storage in an optical computer.
  • the memory device is most suited to storing binary data - either the memory device is written to or not and correspondingly there is presence or absence of an output signal.
  • the memory device is not, however, intrinsically limited to binary data, since it is in fact an analogue device - if the input does not saturate the material, the size of the output depends on the size of the input.
  • the stabilisation of the emitting state is not perfect, but nevertheless, the state is stabilised for up to 100 times the normal lifetime it would have without the photonic lattice, which should be sufficient for many applications; consider modern electronic computers, which have clock speeds of in excess of 1GHz . If it is required to store data for longer periods the memory can be read and the same value written back to the memory.
  • the exemplary memory device of Figure 4 is excited to its stabilised state using photons.
  • phosphors can, as noted above be excited in other ways.
  • electroluminescent materials are particularly useful, as these would provide a bridge between electronics and photonics.
  • a second example is the high efficiency phosphor material of Figure 7.
  • This high efficiency phosphor material 40 is again one in which the basic phosphor material is embedded in a photonic structure arranged to suppress the emission of a photon of a certain frequency.
  • the basic phosphor material, without the photonic structure is one which, under some excitation, has two or more competing photoemission modes.
  • the photonic bandgap of the photonic structure is arranged to suppress, at least in part, at least one of the competing modes. This has the result that the remaining mode or modes produces more light because less of the energy is wasted in the suppressed decay mode.
  • the high energy phosphor may be constructed from a cladded material (Figure 3a) or the materials described in relation to Figure 3b rather than an embedded material ( Figure 1) .
  • Figure 8 is an energy level diagram for a simplified model atom (or ion or molecule etc.) illustrating the operation of the high efficiency phosphor.
  • the atom has been excited to the state E 3 by whatever means.
  • State E 2 decays by two competing modes - one to the ground state E 0 and another to an intermediate state Ei.
  • the photonic bandgap is arranged to suppress the transition to Ei (for example) with the result that the transition to E 0 occurs more often than without the photonic structure. Equally it could be arranged that the transition to E 0 is suppressed enhancing the transition to Ei . (Also it is not essential that one of the competing transitions is to the ground state.)
  • a particular use of the high efficiency phosphor provided by the present invention is in display technology.
  • a phosphor emit a single emission band of light.
  • the photonic bandgap can be then be used to improve, by removing the undesired emission band , the efficiency of a phosphor that produces not only the desired emission band, but also some other emission band as well.
  • Examples of materials whose emissions that can be modified in this way are Y 2 0 3 :Eu 3+ , La 2 0 2 S:Tb 3+ , Y 2 0 2 S:Pr 3+ , Y 2 0 2 S:Tb 3+ , Gd 2 0 2 S:Tb 3+ , InB0 3 :Tb 3+ , InB0 3 :Eu 3+ , Y 2 0 2 S:Eu 3+ .
  • the high efficiency phosphors according to the present invention can be excited by any mechanism.
  • Examples include photoluminescent phosphors (for example, as used in plasma displays and lighting tubes) , and cathodoluminescent phosphors (for example, as used in cathode ray tubes) .
  • Photonic phosphor materials according to the present invention may be made from any phosphor material .
  • Common phosphor materials include inorganic host lattices with rare earth element activators.
  • Rare earth elements include europium and erbium.
  • Rare earth elements are preferably used as dopant (preferably in ionic form) in heavy metal oxides .
  • Heavy metal oxides include Y 2 0 3 , Ta0 2 , Zr0 2 , YNb0 4 and YV0 4 . In some combinations the heavy metal oxides modify the energy levels of the dopant.
  • Alternative carriers for rare earth elements include organic materials.
  • the rare earth elements are incorporated into the organic material as chelated complexes.
  • the ligand is chosen to adjust (if necessary) the energy levels and to enhance the solvation into the material .
  • Organic molecules that have energy levels to which electrons can be excited and which in turn can reemit photons could be used as dopants. These molecules may have triplet excited states that do not reemit photons almost immediately.
  • the photonic bandgap is designed to suppress a photoemission from the phosphor.
  • the position of the bandgap is chosen to match the photoemission of the chosen phosphor.
  • the emission wavelengths of a phosphor are, of course well known or can be measured with spectroscopic techniques.
  • the positions of the bandgaps for particular photonic structures can be measured by spectroscopy, or can be calculated, as is known.
  • a feature of photonic bandgaps is that they are, in general, not identical in all directions. Thus this should be taken into account when designing a photonic phosphor according to the present invention.
  • the bandgap should be controlled to overlap the suppressed emission in as many directions as possible (if not all) .
  • the bandgap was not arranged to overlap the relevant emissions, but in one case (Zr0 2 :Eu 3+ ) to be close to them to provide a measurable modulation of the photonic properties with direction, thus demonstrating the photonic properties, and in another (Ti0 2 :Er 3+ ) the bandgap was placed at some distance, for which the modulation was not present confirming that the modulation seen in the Zr0 2 :Eu 3+ was indeed due to photonic effects.
  • a two dimensional (one layer of spheres deep) photonic lattice was also prepared. This example demonstrates that to experience the photonic properties light usually has to pass through several layers of the refractive index contrast .
  • An example of a geometry in which a two dimensional photonic lattice is, nevertheless, of use to suppress emission was given above.
  • monodisperse anionic latexes were prepared using a variation of the surfactant free polymerisation reaction [see for example, H. Kawaguchi, 2000, Fine Particles edited by T. Sugimoto (New York:
  • a 2 cm square glass cell with walls 2 mm high was used to grow flat PSS template crystals (up to 2 mm x 10 mm on the base of the cell and rods of semicircular cross-section on the walls (up to 1.5 mm x 20 mm) .
  • the spheres are sintered at this stage. Preferably this is done to join the spheres into a continuous matrix. This is thought to increase the communication between the spaces left by spheres (see below) allowing those to be filled in more easily.
  • the infilling of the matrix was achieved utilising sol-gel techniques. These used metal alkoxides in anhydrous methanol solutions in a nitrogen atmosphere in a glove box.
  • the rare earth element (REE) dopants were added to the alkoxides as solutions of the nitrate in anhydrous methanol, allowing the viscous alkoxide to be thinned for easier infilling.
  • the alkoxide solution was pipetted onto the templates covering them and after infilling the crystal was gently cut from the bulk solid.
  • the PSS were eliminated by calcining in air in a furnace (ramped at a rate of l°C/min to 520°C and holding at 8 hours) to obtain periodic arrays of air and rare earth-doped titanium oxide.
  • the anatase phase is formed at this temperature, in preference to the rutile phase, which is formed at higher temperatures.
  • the zirconium oxide was obtained by annealing at a temperature of 650°C.
  • the samples were gold coated for scanning electron microscopy (SEM) and analysed with a Cambridge Instruments Stereoscan 90. This enabled the structure of the materials to be confirmed. It was noted that these photonic structures exhibit a characteristic iridescence in daylight.
  • Figure 9 shows a S.E.M image of one of the microstructured Zr0 2 :Er 3+ lattices, which was fabricated using the sol-gel method (described earlier) and contained approximately 1 mol% of Er 3+ . It is apparent from Figure 9 that the centre-to-centre distance of neighbouring spheres is ca . 400 nm, and that this solid is two dimensional, as only one layer can be seen on the silicon substrate.
  • the anti-Stokes luminescence spectrum obtained from this material under 632.8 nm excitation is shown in Figure 10a, along with the anti-Stokes luminescence spectrum of bulk Zr0 2 :Er 3+ (see Figure 10b) . The latter was not formed using a template and consequently did not consist of a periodic array of the
  • the microstructured solid shows a strong background signal, which increases with wavelength towards the 632.8 nm laser line.
  • the green luminescence which is due to the
  • FIG. 11 shows a S.E.M. image of a periodic air/Zr0 2 :Eu 3+ solid, which was formed in this way. The three dimensional nature of this lattice is apparent from this image, as lower layers are indicated by the black and white contrast superimposed on the top layer.
  • Figure 12 shows three T.E.M.
  • n eff is measured from the centre-to-centre distance of the neighbouring hollow spheres.
  • Fig. 13 presents the anti-Stokes luminescence spectrum of Zr0 2 :Eu 3+ as a function of the angle of incidence of the 632.8 nm laser light.
  • the relative intensities of the anti-Stokes emission bands show variations with the angle of incidence of the exciting laser light. As seen in Figure 13, the bands at 579, 585 and 608 nm display different relative intensities to each other.
  • 5 D 0 level varies with the angle of incidence due to the light levels, which are able to propagate into the lattice; these are modulated by the stopband.
  • the internally emitted light is also modulated by the stopband, and the two effects will give rise to the observed relative intensities.
  • Fig. 14 shows the Stokes emission bands under 514.5 nm excitation as a function of angle of incidence. These bands again show variations in their relative intensities.
  • the green laser light is rejected by the lattice at an angle of incidence around 30°, manifested by a general increase in the background scattering level .
  • the internally emitted light is also modulated by an angle-dependent overlap with the stopband.
  • an inverse photonic lattice prepared from an anti-Stokes phosphor can modulate the intensities of the emitted radiation, when the emitted light is close in energy to the stopband. Therefore it is possible to prepare a photonic anti- Stokes phosphor, which has an overlap of its stopband with intermediate levels in the multiphoton absorption process, in order to inhibit radiative decay from these levels. This enables the lifetimes of these excited levels to be extended, thereby increasing the relative amount of excited state absorption and hence the upconversion efficiency. Materials prepared with this in mind are able to emit strongly at shorter wavelengths than that of the exciting light. Ti0 2 : Er 3+
  • Figure 15 presents a S.E.M. image of an inverse periodic lattice air/Ti0 2 : Er 3+ at 25,800 magnification. It can be seen from this S.E.M. image that the centre-to-centre distance of the hollow spheres is ca. 180 nm. Thus we can predict the wavelength location of the stopband of this material by using the previously mentioned effective medium model, and assuming that the inverse lattice has a f.c.c. structure and that the normal to the deposition layers is along the [111] direction.
  • n e ff the centre-to- centre distance of the neighbouring hollow spheres.
  • the stopband is at a much higher energy than the green anti-Stokes and red Stokes Er 3+ emissions excited by red (632.8 nm) laser light. Consequently no modulation of the emission intensities is observed in either the anti-Stokes ( Figure 16a) or Stokes ( Figure 16b) luminescence spectra.
  • a comparison of the emissions from the periodic air/Ti0 2 : Er 3+ solid with those from the bulk Ti0 2 : Er 3+ solid shows that the intensities of the former are approximately one fifth of the intensities of the latter.
  • the periodic, microstructured solid has ca. 75% by volume of hollow spheres, we would have expected a quarter of the intensity.
  • the observed and expected results are within the experimental errors.
  • the Raman anti-Stokes and Stokes bands of Ti0 2 can also be seen in Figures 16a and 16b, respectively. These bands are indicative of the anatase crystallographic modification which is formed at the calcining temperatures of these experiments (ca. 550°C) .
  • the intensities of these Raman bands obtained from the periodic, microstructured Ti0 2 : Er 3+ lattice are also about one fifth as strong as their counterparts obtained from the bulk Ti0 2 : Er 3+ lattice.

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Abstract

L'invention concerne des matériaux photoniques qui suppriment un mode de photoémission. Un dispositif formant mémoire utilise ce type de matériau à l'aide d'un état stabilisé par la suppression du mode pour représenter la valeur mémorisée. De préférence, les matériaux sont fabriqués en assemblant des sphères de polystyrène comme modèle pour un réseau photonique et en remplissant les espaces entre les matériaux à l'aide d'un premier matéirau, ce qui supprime les sphères et en remplissant ensuite les espaces laissés par les sphères, d'un deuxième matériau. Chaque matériau peut être dopé par un phosphore. Les systèmes de matériaux utilisés (pour un des deux matériaux) comprennent du ZrO2:Er3+, ZrO2:Eu3+, TiO2:Er3+, Y2O3:Eu.
PCT/GB2003/001486 2002-04-12 2003-04-07 Luminophores photoniques et dispositifs WO2003087441A1 (fr)

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WO2006011095A1 (fr) * 2004-07-22 2006-02-02 Philips Intellectual Property & Standards Gmbh Materiaux a bande interdite photonique a luminophores incorpores
DE102005050317A1 (de) * 2005-02-28 2006-08-31 Avago Technologies Ecbu Ip (Singapore) Pte. Ltd. Licht emittierende Vorrichtung mit einer Schicht von photonischen Kristallen mit eingebettetem photolumineszierendem Material und Verfahren zum Herstellen der Vorrichtung
US7358543B2 (en) 2005-05-27 2008-04-15 Avago Technologies Ecbu Ip (Singapore) Pte. Ltd. Light emitting device having a layer of photonic crystals and a region of diffusing material and method for fabricating the device
CN109087984A (zh) * 2017-06-14 2018-12-25 逢甲大学 荧光增益胶膜及其制作方法

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006011095A1 (fr) * 2004-07-22 2006-02-02 Philips Intellectual Property & Standards Gmbh Materiaux a bande interdite photonique a luminophores incorpores
JP2008507839A (ja) * 2004-07-22 2008-03-13 コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ 蛍光体が組み込まれたフォトニックバンドギャップ材料
DE102005050317A1 (de) * 2005-02-28 2006-08-31 Avago Technologies Ecbu Ip (Singapore) Pte. Ltd. Licht emittierende Vorrichtung mit einer Schicht von photonischen Kristallen mit eingebettetem photolumineszierendem Material und Verfahren zum Herstellen der Vorrichtung
US7358543B2 (en) 2005-05-27 2008-04-15 Avago Technologies Ecbu Ip (Singapore) Pte. Ltd. Light emitting device having a layer of photonic crystals and a region of diffusing material and method for fabricating the device
CN109087984A (zh) * 2017-06-14 2018-12-25 逢甲大学 荧光增益胶膜及其制作方法

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