Solid-state white light generating lighting arrangements including photoluminescence wavelength conversion components

Abstract

A white light photoluminescence wavelength conversion component comprises at least one blue light excitable green to yellow light (510 nm to 570 nm) emitting yttrium aluminum garnet (YAG) type phosphor material and at least one blue light excitable orange to red light (585 nm to 670 nm) emitting organic fluorescent dye.

Claims

1. A white light photoluminescence wavelength conversion component comprising: at least one blue light excitable green to yellow light emitting yttrium aluminum garnet type phosphor which, when excited, emits green to yellow light having a peak wavelength in a range 510 nm to 570 nm and at least one blue light excitable orange to red light emitting organic fluorescent dye which, when excited, emits orange to red light having a peak wavelength in a range 585 nm to 670 nm; wherein organic fluorescent dye comprises less than 0.01% by weight of total photoluminescence material formed from a mixture of the at least one blue light excitable orange to red light emitting organic fluorescent dye and the at least one blue light excitable green to yellow light emitting yttrium aluminum garnet type phosphor.

2. The white light photoluminescence wavelength conversion component of claim 1, wherein the at least one yttrium aluminum garnet type phosphor, when excited, emits green light having a peak wavelength in a range 525 nm to 542 nm.

3. The white light photoluminescence wavelength conversion component of claim 1, wherein the at least one yttrium aluminum garnet type phosphor, when excited, emits yellow light having a peak wavelength in a range 545 nm to 570 nm.

4. The white light photoluminescence wavelength conversion component of any claim 1, wherein the orange to red organic fluorescent dye, when excited, emits orange light having a peak wavelength in a range 585 nm to 610 nm.

5. The white light photoluminescence wavelength conversion component of claim 1, wherein the orange to red organic fluorescent dye, when excited, emits red light having a peak wavelength in a range 615 nm to 670 nm.

6. The white light photoluminescence wavelength conversion component of claim 1, wherein the green to yellow yttrium aluminum garnet type phosphor and the orange to red light emitting organic fluorescent dye are incorporated in, and distributed throughout, a light transmissive substrate.

7. The white light photoluminescence wavelength conversion component of claim 1, wherein the green to yellow yttrium aluminum garnet type phosphor and orange to red light emitting organic fluorescent dye comprise at least one layer on a light transmissive substrate.

8. The white light photoluminescence wavelength conversion component of claim 7, wherein the green to yellow yttrium aluminum garnet type phosphor and red to orange light emitting organic fluorescent dye are incorporated in a light transmissive binder and comprise a respective separate layers.

9. The white light photoluminescence wavelength conversion component of claim 1, wherein the green to yellow yttrium aluminum garnet type phosphor material and orange to red light emitting organic fluorescent dye comprise at least one layer on a light reflective substrate.

10. The white light photoluminescence wavelength conversion component of claim 9, wherein the green to yellow yttrium aluminum garnet type phosphor and red to orange light emitting organic fluorescent dye are incorporated in a light transmissive binder and comprise a respective separate layers.

11. The white light photoluminescence wavelength conversion component of claim 1, and further comprising particles of a light scattering material.

12. The white light photoluminescence wavelength conversion component of claim 11, wherein the light scattering material is selected from the group consisting of: magnesium oxide, titanium dioxide, barium sulfate and combinations thereof.

13. The white light photoluminescence wavelength conversion component of claim 11, wherein the light scattering material has a particle size in a range selected from the group consisting of: 0.01 m to 10 m; 0.01 m to 1 m and 0.1 m to 1 m.

14. The white light photoluminescence wavelength conversion component of claim 11, wherein the light scattering material comprises particles of a size such that the particles scatter blue light relatively more than light generated by the at least one green to yellow yttrium aluminum garnet type phosphor.

15. The white light photoluminescence wavelength conversion component of claim 14, wherein the light scattering material has a particle size in a range 100 nm to 150 nm.

16. The white light photoluminescence wavelength conversion component of claim 1, wherein the component, when excited by blue light, generates white light having a color rendering index of at least 80.

17. A white light emitting device comprising: a solid-state light emitter operable to generate blue light having a peak wavelength in a range 430 nm to 490 nm and a white light photoluminescence wavelength conversion component according to claim 1.

18. The white light photoluminescence wavelength conversion component of claim 1, wherein the at least one yttrium aluminum garnet type phosphor has a general composition (Y, M).sub.3(Al, M).sub.5(O, M).sub.12:Ce.sup.3+ in which M is at least one of Tb, Gd, Sm, Lu, La, Sr, Ba, Ca and Mg; M is at least one of Si, Ge, B, P and Ga; and M is at least one of F, Cl, N and S and wherein there is partial substitution of one or more of the Y, Al or O by elements M, M and M respectively.

19. The white light photoluminescence wavelength conversion component of claim 1, wherein the orange to red organic fluorescent dye comprises a perylene based dye or a rhodamine based dye.

20. The white light photoluminescence wavelength conversion component of claim 1, wherein the organic fluorescent dye comprises approximately 0.005% by weight of the total photoluminescence material.

21. The white light photoluminescence wavelength conversion component of claim 1, wherein the organic fluorescent dye comprises approximately 0.00002% by weight of the total photoluminescence material.

22. A white light photoluminescence wavelength conversion component comprising: a polycarbonate light transmissive substrate; at least one blue light excitable green to yellow yttrium aluminum garnet type phosphor, which when excited, emits green to yellow light having a peak wavelength in a range 510 nm to 570 nm; and at least one blue light excitable orange to red light emitting organic fluorescent dye, which when excited, emits orange to red light having a peak wavelength in a range 585 nm to 670 nm; wherein the green to yellow yttrium aluminum garnet type phosphor and the orange to red light emitting organic fluorescent dye are incorporated in, and distributed throughout, the light transmissive polycarbonate substrate; and wherein organic fluorescent dye comprises less than 0.01% by weight of total photoluminescence material formed from a mixture of the organic fluorescent dye and one or more phosphor materials.

Description

DESCRIPTION OF THE DRAWINGS

(1) In order that the present invention is better understood an LED-based lighting arrangement and white light photoluminescence wavelength conversion components in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings in which like reference numerals are used to denote like parts, and in which:

(2) FIG. 1 is schematic representation of an LED-based lighting arrangement in accordance with an embodiment of the invention;

(3) FIG. 2 is a schematic representation of a light transmissive white light photoluminescence wavelength conversion component in accordance with an embodiment of the invention;

(4) FIG. 3 shows the emission spectrum for a 4000K, 80CRI light transmissive white light photoluminescence wavelength conversion component (Example 1) in accordance with an embodiment with the invention;

(5) FIG. 4A to 4C are reliability data for a 4000K, 80CRI light transmissive white light photoluminescence wavelength conversion component (Example 1) in accordance with the invention respectively showing reliability data for: 4A conversion efficacy, 4B relative change of chromaticity (CIE x) and 4C relative change of chromaticity (CIE y);

(6) FIG. 5 shows the emission spectrum for a 3000K, 90CRI light transmissive white light photoluminescence wavelength conversion component (Example 2) in accordance with the invention;

(7) FIG. 6A to 6C are reliability data for a 3000K, 90CRI light transmissive white light photoluminescence wavelength conversion component (Example 2) in accordance with the invention respectively showing reliability data for: 6A relative conversion efficacy, 6B relative change of chromaticity (CIE x) and 6C relative change of chromaticity (CIE y);

(8) FIG. 7 is a schematic representation of a light transmissive white light photoluminescence wavelength conversion component in accordance with an embodiment of the invention which additionally includes light scattering particles;

(9) FIG. 8 is a schematic representation of a light transmissive white light photoluminescence wavelength conversion component in accordance with another embodiment of the invention;

(10) FIG. 9 is a schematic representation of a light transmissive white light photoluminescence wavelength conversion component in accordance with a further embodiment of the invention; and

(11) FIG. 10 is a schematic representation of a light reflective white light photoluminescence wavelength conversion component in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(12) Embodiments of the present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.

(13) Light Transmissive Photoluminescence Wavelength Conversion Components

(14) FIG. 1 illustrates a schematic representation of an LED-based lighting arrangement 10 in accordance with an embodiment of the invention. The lighting arrangement 10 comprises one or more blue light emitting LEDs 12 and a light transmissive white light photoluminescence wavelength conversion component (wavelength conversion component) 14 located remotely to the LED(s) 12. The wavelength conversion component 14 includes at least one blue light excitable green light to yellow light emitting YAG-type (Yttrium Aluminum Garnet) phosphor 16 and at least one blue light excitable orange light to red light emitting organic fluorescent dye 18. To reduce the transfer of heat from the LED(s) 12 to the wavelength conversion component 14, in particular heat transfer to the photoluminescence materials (YAG-type phosphor and organic fluorescent dye), the wavelength conversion component 14 is located remotely to the LEDs, physically separated, by a distance L which is typically a few millimeters. In the context of this specification remote and remotely is used to indicate physically separated by for an air gap typically or light transmissive medium. The blue LED(s) 12 typically comprise GaN-based (gallium nitride-based) LEDs that are operable to generate blue excitation light 20 having an emission peak wavelength .sub.1 in a wavelength range 430 nm to 490 nm (typically 450 nm to 460 nm). The blue LED(s) 12 are configured to irradiate the wavelength conversion component 14 with blue excitation light 20 whereat a proportion is absorbed by the YAG-type phosphor material 16 and organic fluorescent dye 18 which in response respectively emit yellow to green light 22 with an emission peak wavelength .sub.2 in a wavelength range 510 nm to 570 nm and orange to red light 24 with an emission peak wavelength .sub.3 in a wavelength range 585 nm to 670 nm. The emission product 26 of the device 10, which is configured to appear white in color with a selected CCT and CRI (Ra), comprises a combination of blue light 20 (.sub.1) emitted by the LED(s), green to yellow photoluminescence light 22 (.sub.2) generated by the one or more YAG-type phosphor materials and orange to red photoluminescence light 24 (.sub.3) generated by the organic fluorescent dye.

(15) Locating the photoluminescence materials remote to the LED(s) provides a number of benefits compared with known devices in which the phosphor material is provided in direct contact with the light emitting surface of the LED chip in the form of an encapsulant, including reduced thermal degradation of the photoluminescence materials. Additionally, providing the phosphor remotely to the LED(s) over an area many times greater that the light emitting area of the LED chip(s) reduces re-absorption by the LED chip(s) of backscattered excitation light and absorption by the LED chip(s) of photoluminescence light. Furthermore, locating the phosphor remotely enables generation of light of a more consistent color and/or CCT since the phosphor material is provided over a much greater area as compared with providing the phosphor directly on the light emitting surface of the LED.

(16) FIG. 2 illustrates a light transmissive white light photoluminescence wavelength conversion component 14 in accordance with an embodiment of the invention for use in the lighting arrangement 10 of FIG. 1. As indicated in FIG. 2, The wavelength conversion component 14 comprises a light transmissive substrate 30 composed of a light transmissive material, preferably polycarbonate (PC), though in other embodiments it may comprise a poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET), an acrylic, a silicone or thermoform plastics. The YAG-type phosphor 16 and the organic fluorescent dye 18 are incorporated in, and substantially homogeneously distributed throughout, the light transmissive polycarbonate substrate 30. The wavelength conversion component can, as shown, be substantially planar in form or have a 3D form, that is it has a form that defines an internal volume such as for example a hemispherical shell or cylindrical form. The wavelength conversion component is preferably manufactured by extrusion or by injection molding. The YAG-type phosphor 16 and organic fluorescent dye 18 which are both in powder form, are thoroughly mixed in known proportions with a polycarbonate powder and the mixture then pelletized ready for use for extrusion or injection molding. Alternatively, the powders can be mixed in the extrusion/injection molding equipment.

(17) In some embodiments the YAG-type phosphor comprises a green light emitting material which, when excited by blue excitation light, emits light having an emission peak wavelength in a range 525 nm to 542 nm. Alternatively and/or in addition the YAG-type phosphor can comprise a yellow light emitting material which when excited by blue excitation light, emits light having a peak wavelength in a range 545 nm to 570 nm. Typically, the one or more YAG-type phosphor(s) is/are excitable by blue light having a peak wavelength in a range 430 nm to 490 nm. The YAG-type phosphor material comprises particles that are generally spherical in form having an average particle size (D50) of between about 5 m and about 35 m. Typically, the YAG-type phosphor comprises particles of diameter of 10 m to 20 m and preferably of order 15 m.

(18) Within this patent specification YAG-type phosphor material refers to a garnet structured phosphor material containing at least yttrium (Y), aluminum (Al) and oxygen (O) and of general composition Y.sub.3Al.sub.5O.sub.12. Accordingly a YAG-type phosphor includes a cerium (Ce) activated Y.sub.3Al.sub.5O.sub.12:Ce.sup.3+ phosphor generally denoted YAG:Ce. A YAG-type phosphor also encompasses phosphors of general composition (Y, M).sub.3(Al, M).sub.5(O, M).sub.12:Ce.sup.3+ in which there is partial substitution of one or more of the Y, Al or O by elements M, M and M respectively. M can include one or more of terbium (Tb), gadolinium (Gd), samarium (Sm), lutetium (Lu), lanthanum (La), strontium (Sr), barium (Ba), calcium (Ca) and/or magnesium (Mg); M can include one or more of silicon (Si), germanium (Ge), boron (B), phosphorus (P) and/or gallium (Ga) and M can include a halogen such as fluorine (F) or chlorine (Cl), nitrogen (N) and/or sulfur (S). Examples of such phosphors are disclosed in U.S. Pat. No. 8,133,461 B2 and U.S. Pat. No. 8,414,796 B2, both entitled Nano-YAG:Ce Phosphor Compositions and Their Methods of Preparation and U.S. Pat. No. 8,529,791 B2, entitled Green-Emitting, Garnet-Based Phosphors in General and Backlighting Applications, each of which is hereby incorporated by reference in its entirety. The YAG-type phosphor can include any of the NYAG family of phosphors from Intematix Corporation of Fremont, Calif., USA.

(19) Depending on the CRI (Color Rendering Index) of light to be generated by the wavelength conversion component, the orange to red light emitting organic fluorescent dye, when excited by excitation light, emits orange to red light having a peak wavelength in a range 585 nm to 670 nm. In some embodiments the organic fluorescent dye comprises an orange light emitting material which when excited emits light having a peak wavelength in a range 585 nm to 610 nm. Alternatively and/or in addition the organic fluorescent dye is a red light emitting material which when excited emits light having a peak wavelength in a range 615 nm to 670 nm. Examples of suitable organic fluorescent dyes include, but are not limited to, perylene based dyes such as BASF's Lumogen F range of perylene based dyes, such as Lumogen F Red 305 dye which has an emission peak wavelength between 610 nm and 620 nm and Lumogen F Orange 240 dye, which has an emission peak wavelength between 570 nm to 580 nm. Further examples of suitable organic fluorescent dyes include laser dyes such as rhodamine based dyes.

EXAMPLE 1

4000K, 80CRI Light Transmissive Wavelength Conversion Component

(20) The composition of a 4000K, 80CRI light transmissive white light photoluminescence wavelength conversion component (Example 1) in accordance with an embodiment of the invention is given in Table 1. The Example 1 component is composed of a mixture of yellow (551 nm) YAG phosphor, green (543 nm) YAG phosphor and Lumogen F Red 305 organic dye incorporated in, and distributed throughout, a polycarbonate substrate (FIG. 2). The component is typically of a thickness of about 1.5 mm. The yellow (551 nm) YAG phosphor comprises a YAG:Ce.sup.3+ phosphor of general composition Y.sub.3(Al, Ba).sub.5(O, F).sub.12:Ce.sup.3+ and the green (543 nm) YAG phosphor comprises a YAG:Ce.sup.3+ phosphor of general composition Y.sub.3(Al, Lu, Ba).sub.5(O, F).sub.12:Ce.sup.3+. As can be seen from Table 1, the yellow (551 nm) and green (543 nm) YAG phosphors each constitute 49.997% by weight of the total photoluminescence materials whilst the organic fluorescent dye constitutes only 0.005% of the total weight of luminescent materials.

(21) TABLE-US-00001 TABLE 1 Example 1: 4000K, 80CRI light transmissive photoluminescence wavelength conversion component composition Photoluminescence Weight material Constituent (grams) Total weight % Weight % Polycarbonate 469.50 93.90% Yellow (551 nm) 15.25 3.05% 49.997% YAG phosphor Green (543 nm) 15.25 3.05% 49.997% YAG phosphor Lumogen R 305 dye 0.00164 0.000003% 0.005% Total 500 100% 100%

(22) For comparison purposes, the composition of a known 4000K, 80CRI light transmissive photoluminescence wavelength conversion component (Reference) using all inorganic phosphors is given in Table 2. The Reference component is composed of a mixture of yellow (556 nm) YAG phosphor, green (540 nm) YAG phosphor and red (626 nm) nitride phosphor. The yellow (556 nm) YAG phosphor comprises a YAG:Ce.sup.3+ phosphor of general composition Y.sub.3(Al, Ba).sub.5(O, F).sub.12:Ce.sup.3+, the green (540 nm) YAG phosphor comprises a YAG:Ce.sup.3+ phosphor of general composition Y.sub.3(Al, Ga, Ba).sub.5(O, F).sub.12:Ce.sup.3+ and the red (626 nm) nitride phosphor a phosphor of general composition (Ca, Sr)AISiN.sub.3:Eu. As can be seen from Table 2 the yellow (556 nm) and green (540 nm) YAG phosphors constitute about 22% and 64% respectively by weight of the total photoluminescence materials whilst the red phosphor constitutes about 14% of the total weight of luminescent materials.

(23) TABLE-US-00002 TABLE 2 Reference: 4000K, 80CRI light transmissive photoluminescence wavelength conversion component composition Photoluminescence Constituent Weight (grams) Total weight % material Weight % Polycarbonate 481.50 96.3% Yellow (556 nm) 4.00 0.80% 21.5% YAG phosphor Green (540 nm) 2.59 0.52% 64.44% YAG phosphor Red (626 nm) 11.92 2.38% 14.02% nitride phosphor Total 500 100% 100%

(24) FIG. 3 shows measured emission spectrum (intensity versus wavelength) for i) the Example 1 wavelength conversion component (solid line) and ii) the Reference wavelength conversion component (dash line). Table 3 gives various characteristics of the wavelength conversion components Example 1 and Reference. As will be noted from FIG. 3 and Table 3, the photoluminescence wavelength conversion component (Example 1) in accordance with the invention performs better than the equivalent known wavelength conversion component (Reference) based solely on inorganic phosphors. As described above, the red phosphor constitutes about 14% of the total weight of photoluminescence materials of the Reference component. In terms of overall component cost, the cost of the red phosphor represents 30% of the total component cost per unit weight ($.Math.kg.sup.1). In contrast for photoluminescence wavelength conversion components in accordance with the invention (e.g., Example 1), the cost of the organic fluorescent dye represents less than 0.01% of the total component cost per unit weight ($.Math.kg.sup.1) (based on the weight cost ($.Math.kg.sup.1) of organic fluorescent dyes being five times that of red phosphor). It will be appreciated that for high CRI photoluminescence wavelength conversion components in accordance with the invention these virtually eliminate the cost associated with the orange to red photoluminescence material(s). As a result, wavelength conversion components in accordance with the invention can be less expensive by 30% or more compared with known photoluminescence wavelength conversion components based solely on inorganic phosphor materials. Such a cost saving represents a significant technical advantage over the known solutions.

(25) TABLE-US-00003 TABLE 3 Light transmissive wavelength conversion components measured performance Conversion Luminous Quantum Stokes CCT CRI Efficacy Efficacy Efficiency Efficiency Component (K) CIE x CIE y R.sub.a R9 (Lm/bW) (Lm/wW) (%) (%) Example 1 4019 0.3818 0.3859 81.8 5.3 232.9 336.5 86.61 79.88 Reference 4019 0.3818 0.3747 79.6 10.9 217.7 326.3 83.69 79.38 Example 2 3031 0.4338 0.3976 92.6 39.7 207.2 315.9 84.64 77.18

(26) FIG. 4A to 4C are reliability data for wavelength conversion component Example 1 under accelerated testing conditions 85 C./85% RH (solid line) and under room temperature conditions (dashed line). The figures respectively show: 4A relative conversion efficacy (conversion efficacy relative to conversion efficacy at time t=0) versus time, 4B relative change of chromaticity (CIE x) (change in CIE x relative to CIE x at time t=0) versus time and 4C relative change of chromaticity (CIE y) (change in CIE y relative to CIE y at time t=0) versus time. All measured reliability data are for an excitation light irradiance of 110 mW.Math.cm.sup.2.

EXAMPLE 2

3000K, 90CRI Light Transmissive Wavelength Conversion Component

(27) The composition of a 3000K, 90CRI light transmissive photoluminescence wavelength conversion component (Example 2) in accordance with the invention is given in Table 4. The Example 2 conversion component is composed of a mixture of yellow (558 nm) YAG phosphor, green (531 nm) YAG phosphor and Lumogen F Red 305 organic dye incorporated in, and distributed throughout, a polycarbonate substrate. The component is typically of a thickness of about 1.5 mm. The yellow (558 nm) YAG phosphor comprises a YAG:Ce.sup.3+ phosphor of general composition Y.sub.3(Al, Ba).sub.5(O, F).sub.12:Ce.sup.3+. The green (531 nm) YAG phosphor comprises a YAG:Ce.sup.3+ phosphor of general composition Y.sub.3(Al, Ga, Ba).sub.5(O, F).sub.12. As can be seen from Table 4 the yellow (558 nm) and green (531 nm) YAG phosphors each constitute 49.99994% by weight of the total photoluminescence materials whilst the organic fluorescent dye constitutes only 0.00002% of the total weight of luminescent materials.

(28) TABLE-US-00004 TABLE 4 Example 2: 3000K, 90CRI light transmissive photoluminescence wavelength conversion component composition Photoluminescence Weight material Constituent (grams) Total Weight % Weight % Polycarbonate 459.5 91.9% Yellow (558 nm) 20.25 4.05% 49.99994% YAG phosphor Green (531 nm) 20.25 4.05% 49.99994% YAG phosphor Lumogen R 305 0.00458 0.000009% 0.00002% dye Total 500 100% 100%

(29) FIG. 5 shows the measured emission spectrum (intensity versus wavelength) for wavelength conversion component Example 2. Table 3 above, also gives various characteristics of the wavelength conversion component Example 2. By comparison with a known wavelength conversion component based solely on phosphors having the same nominal emission characteristics, the inventors have determined that photoluminescence wavelength conversion component in accordance with the invention (Example 2) perform as well as the known wavelength conversion components. The red phosphor in such known wavelength conversion components having an equivalent performance, typically constitute about 30% of the total component cost ($.Math.kg.sup.1). In contrast for photoluminescence wavelength conversion components in accordance with the invention (Example 2) the organic fluorescent dye represents less than 0.000003% of the total component cost per unit weight ($.Math.kg.sup.1) (based on the weight cost ($.Math.kg.sup.1) of organic fluorescent dyes is five times that of red phosphor). It will be appreciated that for high CRI photoluminescence wavelength conversion components in accordance with the invention, such components virtually eliminate the costs associated with the orange to red photoluminescence material(s). As a result, wavelength conversion components in accordance with the invention can be less expensive by 30% or more compared with known photoluminescence wavelength conversion components based solely on inorganic phosphor materials.

(30) FIG. 6A to 6C are reliability data for wavelength conversion component Example 2 under accelerated testing conditions 85 C./85% RH (solid line) and under room temperature conditions (dashed line). The figures respectively show: 6A relative conversion efficacy (conversion efficacy relative to conversion efficacy at time t=0) versus time, 6B relative change of chromaticity (CIE x) (change in CIE x relative to CIE x at time t=0) versus time and 6C relative change of chromaticity (CIE y) (change in CIE y relative to CIE y at time t=0) versus time. All measured reliability data are for an excitation light irradiance of 110 mW.Math.cm.sup.2.

(31) FIG. 7 illustrates a light transmissive photoluminescence wavelength conversion component 14 in accordance with an embodiment of the invention that additionally includes light scattering particles 32. The inclusion of light scattering particles is found to increase photoluminescence light generation thereby enabling a reduction in the quantity of YAG-type phosphor 16 required to generate a given color of emitted light. It is believed that the increase in photoluminescence light generation results from the light scattering material increasing the probability of collisions of the photons with particles of the phosphor material. In some embodiments, the inclusion of the light scattering material can potentially, for a given emission product color and intensity, reduce phosphor material usage by 33% or more. Additionally, the inclusion of light scattering particles can improve color uniformity of emitted light and Color Over Angle (COA) of the emitted light by reducing any variation in light color with angle.

(32) Examples of light scattering materials include particles of Zinc Oxide (ZnO), titanium dioxide (TiO.sub.2), barium sulfate (BaSO.sub.4), magnesium oxide (MgO), silicon dioxide (SiO.sub.2) or aluminum oxide (Al.sub.2O.sub.3). In some embodiments the light scattering material comprises a white ink such as for example Norcote International Inc's super white ink GN-027SA which already includes particles of a highly light reflective material, typically TiO.sub.2.

(33) In some embodiments, the light scattering material utilized within the wavelength conversion component has a particle size that is selected such that the scattering particles will scatter blue excitation light relatively more than they will scatter light generated by the photoluminescence materials. For example, the light scattering particle size may be selected such that the particles will scatter blue excitation light relatively at least twice as much as they will scatter light generated by the at least one phosphor material. This ensures that a higher proportion of the blue excitation light will be scattered, increasing the probability of the photon interacting with a phosphor material particle and resulting in the generation of photoluminescence light. At the same time photoluminescence generated light can pass through with a lower probability of being scattered.

(34) Since this approach can further increase the probability of blue photons interacting with a phosphor material particle, less phosphor material is required to generate a selected emission color. This arrangement can also increase luminous efficacy of the wavelength conversion component/device. In some embodiments the light scattering material comprises particles with an average particle size of less than about 150 nm and typically has an average particle size in a range 40 nm to 150 nm. Particles of such size will Mie scatter light differently depending on the light wavelength. The particle size of the light diffusive material can be selected to scatter excitation light more than photoluminescence generated light. Where the excitation light comprises blue light the particles of light diffusive material preferably have an average particle size of about 60 nm. In other embodiments, the light scattering material has an average particle size in a range 1 m to 50 m and more preferably in a range 10 m to 20 m.

(35) In other embodiments, and as shown in FIGS. 8 and 9, the YAG-type phosphor 16 and organic fluorescent dye 18 comprise at least one layer on the light transmissive substrate 30. The YAG-type phosphor 16 and organic fluorescent dye 18 which are both in powder form, are thoroughly mixed in known proportions with a light transmissive binder material 34 (for example a thermally or UV curable silicone) and the mixture then deposited as one or more substantially uniform thickness layers on the surface of the light transmissive substrate 30. The YAG-type phosphor 16 and organic fluorescent dye 18 can be incorporated together in a single layer as shown in FIG. 8 or comprise respective separate layers as illustrated in FIG. 9. Typically, the light transmissive binder 34 comprises a curable liquid polymer such as a polymer resin, a monomer resin, an acrylic, an epoxy, a silicone or a fluorinated polymer. Alternatively, the YAG-type phosphor and organic fluorescent dye can be combined with a clear ink such as for example Nazdar's UV curable litho clear overprint PSLC-294 to form a phosphor ink. In one embodiment the phosphor ink is deposited on the light transmissive substrate 30 by screen printing with the thickness t of the one or more layers be controlled by the number of printing passes. As will be apparent to those skilled in the art the YAG-type phosphor/organic fluorescent dye/binder mixture can be applied using other methods including inkjet printing, spin coating, slot die coating, roller coating, drawdown coating or sweeping the mixture over the surface using a blade such as a squeegee (e.g. doctor blading). The light transmissive substrate 30 preferably comprises a polycarbonate, acrylic, a glass or a silicone.

(36) Light Reflective Photoluminescence Wavelength Conversion Components

(37) In other embodiments the wavelength conversion component can be light reflective. A light reflective wavelength conversion component 36 in accordance with an embodiment of the invention is shown in FIG. 10. For a light reflective wavelength conversion component 36 the YAG-type phosphor 16 and organic fluorescent dye 18 comprise one or more layers on a light reflective surface of the substrate 38. The YAG-type phosphor 16 and organic fluorescent dye 18 are incorporated in a light transmissive binder 34 and the mixture then deposited as one or more layers on the surface of the light reflective substrate. Similar to the embodiments of FIGS. 8 and 9, the YAG-type phosphor 16 and organic fluorescent dye 18 can be incorporated together in a single layer as shown in FIG. 7 or in respective separate layers. Typically, the light transmissive binder 34 comprises a curable liquid polymer such as a polymer resin, a monomer resin, an acrylic, an epoxy, a silicone or a fluorinated polymer. The one or more layers containing the YAG-type phosphor 16 and organic fluorescent dye 18 can be deposited as a substantially uniform thickness layer on the light reflective substrate 38 by screen printing, slot die coating, spin coating, roller coating, drawdown coating or doctor blading. The light reflective substrate can comprise any material having a high light reflectivity surface, typically a reflectance of 0.9 or higher, such as a highly reflective paper, a high reflectance polymer material such as a polycarbonate, acrylic, or metallic material such as silver, aluminum, chromium. To assist in the dissipation of heat the light reflective surface can be thermally conductive.