PHOSPHOR PARTICLE COATING

Abstract

The invention provides a method for providing a luminescent particle (100) with a hybrid coating, the method comprising: (i) providing a luminescent core (102) comprising a primer layer (105) on the luminescent core (102); (ii) providing a main ALD coating layer (120) onto the primer layer (105) by application of a main atomic layer deposition process, the main ALD coating layer (120) comprising a multilayer (1120) with two or more layers (1121) having different chemical compositions, and wherein in the main atomic layer deposition process a metal oxide precursor is selected from a group of metal oxide precursors comprising Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V; (iii) providing a main sol-gel coating layer (130) onto the main ALD-coating layer (120) by application of a main sol-gel coating process, the main sol-gel coating layer (130) having a chemical composition different from one or more of the layers (1121) of the multilayer (1120).

Claims

1. A method for providing a luminescent particle with a hybrid coating, the method comprising: providing a particulate luminescent material having a surface; forming a primer layer directly on at least a portion of the surface; performing a first atomic layer deposition process on the particulate luminescent material having the primer layer to deposit a first ALD layer, the first atomic layer deposition process using a metal oxide first precursor selected from a group of metal oxides comprising Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V; performing a second atomic layer deposition process to deposit a second ALD layer onto the first ALD layer, the second atomic layer deposition process using a metal oxide second precursor different from the first precursor and selected from a group of metal oxides comprising Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V; and performing a main sol-gel coating process to form a main sol-gel coating layer directly onto the second ALD layer, the main sol-gel coating layer having a chemical composition different from the first ALD layer and the second ALD layer.

2. The method according to claim 1, wherein forming the primer layer directly onto at least a portion of the surface of the particulate luminescent material comprises performing a primer sol-gel coating process on the particulate luminescent material, the primer sol-gel coating process using a metal alkoxide precursor.

3. The method according to claim 2, wherein the primer sol-gel coating process comprises: suspending the particulate luminescent material in an alcohol-aqueous ammonia solution mixture; adding the metal alkoxide precursor to the mixture; stirring the mixture containing the metal alkoxide until the primer layer is formed; washing the particulate luminescent material having the primer layer with alcohol; and drying the particulate luminescent material having the primer layer.

4. (canceled)

5. The method according to claim 1, further comprising washing the particulate luminescent material in a washing solvent before forming the primer layer, the washing solvent having a pH<7.

6-7. (canceled)

8. The method according to claim 5, wherein the washing solvent comprises a weak acid and equal to or less than 50% wt/wt water, and washing the particulate luminescent material further comprises: successively subjecting the particulate luminescent material to a drying treatment.

9. (canceled)

10. The method according to claim 1, wherein: the primer layer has a primer layer thickness (d1) in the range of 0.1-5 nm, the first ALD layer and second ALD layer form a main ALD coating layer, and the main ALD coating layer has a main ALD coating layer thickness (d2) in the range of 5-250 nm; and the main sol-gel coating layer has a main sol-gel coating layer thickness (d3) in the range of 50-700 nm.

11. (canceled)

12. The method according to claim 1, wherein the main sol-gel coating process comprises: providing a mixture of an alcohol, ammonia, water, the particulate luminescent material having the primer layer and the first ALD layer and the second ALD layer, and a metal alkoxide precursor while agitating the mixture, and allowing a main sol-gel coating layer to be formed directly onto the second ALD layer, the metal alkoxide precursor is titanium alkoxide, silicon alkoxide, and or aluminum alkoxide; and retrieving the particulate luminescent material having the primer layer, the first ALD layer and the second ALD layer and the main sol-gel coating layer from the mixture and subjecting the retrieved particulate luminescent material having the primer layer, the first ALD layer and the second ALD layer and the main sol-gel coating layer to a heat treatment.

13. (canceled)

14. The method according to claim 1, comprising: successively providing n additional ALD layers, wherein 2≤n≤10, between the first ALD layer and the second ALD layer, each additional ALD layer has an additional ALD layer coating layer thickness (d21) in the range of 1-20 nm, one or more additional ALD layers comprise one or more metal oxides selected from a group of HfO.sub.2, ZrO.sub.2, TiO.sub.2, and Ta.sub.2O.sub.5, one or more additional ALD layers comprise Al.sub.2O.sub.3, and the second ALD consist of one or more metal oxides selected from the group of HfO.sub.2, ZrO.sub.2, TiO.sub.2, and Ta.sub.2O.sub.5.

15. The method according to claim 1, further comprising: providing a further ALD coating layer onto the main sol-gel coating by application of a further atomic layer deposition process, in the further atomic layer deposition process a further metal oxide precursor is selected from a group of metal oxides comprising Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V, the further ALD coating layer has a further ALD coating layer thickness (d4) in the range of 10-50 nm, and the further ALD coating layer comprises two or more layers having different chemical compositions, one or more of the layers comprise metal oxides selected from a group of Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, HfO.sub.2, SnO.sub.2, ZnO and Ta.sub.2O.sub.5, and the two or more layers have a chemical composition differing from the chemical composition of the main sol-gel coating layer.

16. (canceled)

17. The method according to claim 1, wherein the surface of the particulate luminescent material comprises an alkaline earth element, aluminum, and oxide, wherein the alkaline earth element comprises strontium.

18. (canceled)

19. (canceled)

20. The method according to claim 1, wherein the particulate luminescent material is selected from a group consisting of (i) the SrLiAl.sub.3N.sub.4:Eu.sup.2+ class, and (ii) the SrLi.sub.2Al.sub.1.995Si.sub.0.005O.sub.1.995N.sub.2.005:Eu.sup.2+ class.

21-22. (canceled)

23. A luminescent material comprising: a particulate luminescent material having a surface; a primer layer disposed on and in contact with the surface of the particulate luminescent material, the primer layer comprising a primer layer metal oxide and having a thickness in the range of 0.1-5 nm; a first ALD layer disposed on and in contact with the primer layer and any portion of the surface of the particulate luminescent material not covered with the primer layer, the first ALD layer comprising a first oxide of one or more of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V, and different from the primer layer metal oxide; a second ALD layer disposed on and in contact with the first ALD layer, the second ALD layer comprising a second oxide of one or more of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V, and different from the first oxide, the first ALD layer and second ALD layer forming a main ALD layer having a thickness in the range of 5-250 nm; and a main sol-gel coating layer disposed on the second ALD layer, wherein the main sol-gel coating has a main sol-gel coating layer thickness (d3) in the range of 50-700 nm, wherein the main sol-gel coating layer has a chemical composition differing from the first ALD layer and the second ALD layer.

24. The luminescent material according to claim 23, wherein at least a portion of the surface of the particulate luminescent material comprises an oxide.

25. The luminescent material according to claim 24, wherein at least a portion of the surface of the particulate luminescent material comprises an alkaline earth element and aluminum, wherein the alkaline earth element comprises strontium.

26-27. (canceled)

28. The luminescent material according to claim 23, wherein the particulate luminescent material is selected from a group consisting of (i) the SrLiAl.sub.3N.sub.4:Eu.sup.2+ class, and (ii) the SrLi.sub.2Al.sub.1.995Si.sub.0.000O.sub.1.995N.sub.2.005:Eu.sup.2+ class.

29. The luminescent material according to claim 23, further comprising a further ALD coating layer arranged onto the main sol-gel coating layer, the further ALD coating layer having a further ALD coating layer thickness (d4) in the range of 10-50 nm, the further ALD coating layer comprises a further multilayer with two or more layers having different chemical compositions, one or more of the layers comprising metal oxides selected from a group of Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, HfO.sub.2, SnO.sub.2, ZnO and Ta.sub.2O.sub.5, and the two or more layers having a chemical composition differing from the chemical composition of the main sol-gel coating layer.

30-31. (canceled)

32. The luminescent material according to claim 23, further comprising n additional ALD layers, wherein 2≤n≤10, between the first ALD layer and the second ALD layer, each additional ALD layer having an additional ALD layer coating layer thickness (d21) in the range of 1-20 nm, and one or more of the additional ALD layers comprise one or more metal oxides selected from a group of HfO.sub.2, ZrO.sub.2, TiO.sub.2, and Ta.sub.2O.sub.5.

33-35. (canceled)

36. A display system comprising: a light emitting diode array, the light emitting diode array including a plurality of phosphor converted light emitting diodes, each phosphor converted light emitting diode including a wavelength converter comprising the luminescent material of claim 23; a display; and a lens or lens system spaced apart from the light emitting diode array and arranged to couple light from the light emitting diode array into the display.

37. A mobile device comprising: a camera; and a flash illumination system comprising: a light emitting diode array including a plurality of light emitting diodes, each light emitting diode including a wavelength converter comprising the luminescent material of claim 23.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0145] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0146] FIG. 1 schematically depicts aspects of a luminescent particle;

[0147] FIG. 2a-2b schematically depict some further aspects of a luminescent particle;

[0148] FIG. 3 schematically depicts a lighting device;

[0149] FIG. 4a-4b show a SEM and a TEM image of a luminescent particle;

[0150] FIGS. 5a-5b show some experimental results wherein embodiments of the invention are compared to prior art luminescent materials.

[0151] FIGS. 6a-6b show, respectively, cross-sectional and top schematic views of an array of pcLEDs.

[0152] FIG. 7a shows a schematic top view of an electronics board on which an array of pcLEDs may be mounted, and FIG. 7b similarly shows an array of pcLEDs mounted on the electronic board of FIG. 7a.

[0153] FIG. 8a shows a schematic cross-sectional view of an array of pcLEDs arranged with respect to waveguides and a projection lens. FIG. 8b shows an arrangement similar to that of FIG. 8a, without the waveguides.

[0154] FIG. 9 schematically illustrates an example camera flash system comprising an adaptive illumination system.

[0155] FIG. 10 schematically illustrates an example display (e.g., AR/VR/MR) system that includes an adaptive illumination system.

[0156] The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0157] FIG. 1 schematically depicts an embodiment of the luminescent particles 100. The luminescent particle 100 comprises a luminescent core 102 comprising a primer layer 105 on the luminescent core 102. Herein the luminescent core 102 with the primer layer 105 is also referred to as a primer layer 105 comprising luminescent particle 100. The primer layer 105 has a chemical composition differing from the chemical composition of the core 102. The luminescent core 102 may include e.g. micrometer dimensional particles of a luminescent nitride or sulfide phosphor but may also include other (smaller) material such as luminescent nanoparticles (see further FIG. 2b).

[0158] The luminescent particle 100 further comprises a main ALD coating layer 120. In the depicted embodiment the main ALD coating layer 120 comprises a multilayer 1120 with three layers 1121, layer 1121a, layer 1121b, and layer 1121c. The three layers 1121a, 1121b, 1121c especially have (at least two) different chemical compositions. Especially adjacently (and contacting) arranged layers 1121 have different compositions. Moreover, one or more of the layers 1121 of the multilayer 1120 may have chemical compositions (also) differing from the chemical composition of the primer layer 105. The layers 1121 may in embodiments e.g. comprise different oxides of Al, Zn, Hf, Ta, Zr, Ti, Sn, Nb, Y, Ga, and V. Additionally or alternatively, the layers 1121 may comprise Si and/or Ge. Especially one of the layers 1121 may be an alumina layer.

[0159] The luminescent particle 100 further comprises a main sol-gel coating layer 130, especially having a chemical composition differing from one or more of the layers 1121 of the multilayer 1120. The figure further shows that main ALD coating layer 120 is arranged between the primer layer 105 and the main sol-gel layer 130. Especially, adjacently arranged/contacting coating layers may have different compositions. In the depicted figure, layer 1121a especially has a composition that differs from the composition of the main sol-gel layer 130. Layer 1121c especially has a composition that differs from the composition of the primer layer 105. The hybrid coating of the embodiment in FIG. 1 thus comprises a primer layer 105, a main ALD layer 120 and a main sol-gel coating layer 130. In further embodiments, see e.g. FIG. 2a, the hybrid coating further comprises a further ALD coating layer 140.

[0160] The embodiment of FIG. 2a also comprises a further ALD coating layer 140 arranged on the main sol-gel coating layer 130. In the depicted embodiment, the further ALD coating layer 140 (also) comprises a further multilayer 1140 comprising two (further sub) layers 1141, 1141a, 1141b (of the further multilayer 1140). Yet, in other embodiments the further ALD coating layer 140 is (deposited as) a single layer. In FIG. 2a also the thicknesses of the layers are indicated. It is noted that the thicknesses are not to scale and only are depicted to explain the meaning of the terms and show the location. The primer layer thickness is indicated by the reference d1. The primer layer thickness d1 may be in the range of 0.1-5 nm. The ALD coating layer thickness is indicated with the reference d2. The ALD coating layer thickness d2 may especially be in the range of 5-250 nm. The thickness of the main sol-gel coating 130 is indicated with reference d3. The main sol-gel coating layer thickness d3 is generally larger than the ALD coating layer thickness d2. The main sol-gel coating layer thickness d3 is especially in the range of 50-700 nm. The depicted embodiment comprises a multilayer 1120 with three layers 1121, each layer 1121 having a layer coating layer thickness d21 in the range of 1-20 nm. In the depicted embodiment, the layer coating thickness d21 of the three layers 1121 is about the same. The layer coating thickness d21 may though vary between the different layers 1121, see e.g. FIG. 4b. The three layers 1121a, 1121b and 1121c may e.g. depict alternating Al.sub.2O.sub.3 layers (by way of example 1121b) and Ta.sub.2O.sub.5 layers (by way of example 1121a,1121c). The (further sub) layer coating layer thickness (not indicated with a reference) of the (further sub) layers 1141 of the further multilayer 1140 may especially be in the ranges as described in relation to the layer coating layer thickness d21 of the layers 1121 of the multilayer 1120.

[0161] FIG. 2a further schematically depicts that the primer layer 105 comprises an oxide-containing layer 101 and a primary sol-gel layer 110. The oxide-containing layer 101 is arranged at a surface 67 of the core 102. In the embodiment, the oxide-containing layer 101 and the primary sol-gel layer 110 are continuous and conformal. Yet, in further embodiments, this may not be the case, and e.g. the main ALD coating layer 120 may contact the oxide-containing layer 101 at some locations and may even contact the surface 67 of the core at some further location (while contacting the primary sol-gel layer 110 at other locations.

[0162] FIG. 2a further indicates with references 17, 27, 37, 47, 57 the surfaces of respective layers, and with reference 67 the surface of the core 102. As indicated above, the layer thicknesses described herein are especially average layer thicknesses. Especially at least 50%, even more especially at least 80%, of the area of the respective layers have such indicated layer thickness. Hence, referring to the thickness d2 between surface 47 and surface 37, below at least 50% of surface 37, a layer thickness in the range of e.g. 5-250 nm may be found, with the other less than at least 50% of the surface area 37 e.g. smaller or larger thicknesses may be found, but in average d2 of the main ALD coating (multi-)layer 120 is in the indicated range of 5-250 nm. Likewise, this may apply to the other herein indicated thicknesses. For instance, referring to the thickness d3 between surface 37 and surface 27, this thickness may over at least 50% of the area of 27 be in the range of 50-700 nm, with the other less than at least 50% of the surface area 27 e.g. smaller or larger thicknesses may be found, but in average d1 of the first layer main sol-gel layer 130 is in the indicated range of 50-700 nm, such as especially 100-500 nm.

[0163] FIG. 2b schematically depicts an embodiment wherein the luminescent core 102 includes a luminescent nanoparticle, here by way of example a quantum dot 160. The quantum dot in this example comprises a quantum rod with a (semiconductor) core material 161, such as ZnSe, and a shell 162, such as ZnS. Of course, other luminescent nanoparticles may also be used. Such luminescent quantum dot 160 can also be provided with the hybrid coating.

[0164] FIGS. 1-2 schematically depict luminescent particles 100 having a single nucleus. However, optionally also aggregates encapsulated with the hybrid coating may be formed. This may especially apply for quantum dots as luminescent particles defining the luminescent core 102.

[0165] The figures especially depict embodiments of the coating architecture on phosphor particles or luminescent cores 102 (after applying the respective (ALD and sol-gel) coating processes). The phosphor particles 102 may be covered by an oxide layer 101 formed by a washing and baking process. The primary sol-gel coating 110 comprises in embodiments silicon oxide (SiO.sub.2) provided by a (primary) sol-gel coating process. The first SiO.sub.2 layer 110 especially acts as nucleation or seed layer for the main ALD coating layer 120, provided by a main atomic layer deposition process. Therefore, (the primary layer 105 as well as) the primary sol-gel coating layer 110 does not need to form a conformal or fully closed coating around each core 102. The primary sol-gel coating layer 110, e.g. the primary SiO.sub.2 layer 110 can also be seen as a surface treatment to provide OH-groups on the phosphor particles 102. Such OH-groups may assist the ALD precursors to bond on the surface and consequently initiate film growth.

[0166] The main ALD coating layer 120 especially comprises a multilayer 1120 also called “nanolaminate” 1120 of metal oxides (sub-)layers 1121. A nanolaminate 1120 may form an extremely dense and nearly pinhole free conformal coating on phosphor particles that is almost impermeable to gases like water vapor and oxygen. The nanolaminate protection layer 1120 may in embodiments have a thickness d2 of 20-50 nm consisting of more than two sub-layers of Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, HfO.sub.2, SnO.sub.2, ZnO or Ta.sub.2O.sub.5. Each layer 1121 may have a thickness d21 in the range of 1 nm-15 nm. The outer layer 1121, i.e. the layer (1121a in FIGS. 1 and 2a) contacting the main sol gel coating layer 130 is in embodiments a chemical stable layer such as HfO.sub.2, ZrO.sub.2 or Ta.sub.2O.sub.5 that does not corrode when exposed to water or other solvents such as cyclohexanone.

[0167] The main sol-gel coating layer 130 may also comprise silicon oxide (SiO.sub.2) provided by the (main) sol-gel coating process, analog to the primary sol-gel coating layer 110. The main sol-gel coating 130 may especially function as mechanical protection to prevent damage of the underlying barrier coating 120. In an LED fabrication process phosphor particles undergo various process steps, such as mixing, sieving, pressing, and molding. These process steps may induce mechanical stress in the coating. As a results the coating might be damaged. The main sol-gel coating layer 130 provides a high robustness against post-processing and fabrication steps. In embodiments a high reliability can be guaranteed by applying the main sol-gel coating layer 130 layer on the luminescent particles 100.

[0168] In embodiments of the invention, a further ALD coating layer 140 is added to the layer architecture, as depicted in FIG. 2a. The further ALD coating layer 140 in the embodiment comprises a nanolaminate 1140. The layer 140 or multilayer 1140 may comprise metal oxides such as Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, HfO.sub.2, SnO.sub.2, ZnO or Ta.sub.2O.sub.5. The total thickness d4 of the layer 140 is especially in the range of 10-50 nm. The further ALD coating layer 140 may further stabilize the overall coating structure by filling pores and pin-holes in the main sol-gel coating layer 130. In addition, the further ALD coating layer 140 can suppress the surface reactivity of the main sol-gel layer 130. This surface reactivity may be in embodiments of LED manufacturing processes be advantageous for maintaining the rheology or other properties of certain silicone phosphor slurries.

[0169] FIG. 3 schematically depicts a lighting device 20 comprising a light source 10 configured to generate light source radiation 11, especially one or more of blue and UV, as well as a wavelength converter 30 comprising the luminescent material 1 with particles 100 as defined herein. The wavelength converter 30 may e.g. comprise a matrix, such as a silicone or organic polymer matrix as described above, with the coated particles 100 embedded therein. The wavelength converter 30 is configured to (wavelength) convert at least part of the light source radiation 11 into wavelength converter light 31. Optionally also light source radiation 11 may pass the wavelength converter 30 (without being converted). The wavelength converter light 31 at least includes luminescence from the herein described coated particles 100. However, the wavelength converter 30 may optionally include also one or more other luminescent materials. The wavelength converter 30, or more especially the luminescent material 1, may be arranged at a non-zero distance d30, such as at a distance of 0.1-100 mm. However, optionally the distance d30 may be zero, such as e.g. when the luminescent material is embedded in a dome on a LED die. The distance d30 is the shortest distance between a light emitting surface of the light source 10, such as a LED die, and the wavelength converter 30, more especially the luminescent material 1.

[0170] The light source 10 may be an LED, such that lighting device 20 is a phosphor-converter LED (“pcLED”). For example, light source 10 may be a III-Nitride LED that emits ultraviolet, blue, green, or red light. LEDs formed from any other suitable material system and that emit any other suitable wavelength of light may also be used. Other suitable material systems may include, for example, III-Phosphide materials, III-Arsenide materials, and II-VI materials.

[0171] FIG. 4a shows a SEM image of luminescent material 1 comprising some coated luminescent particles 100. In FIG. 4b a TEM image of a coated luminescent particle 100 is given, clearly showing or core 102 with an oxide-containing layer 101, a primary (SiO.sub.2) sol-gel coating layer 110, a main ALD coating layer 120, comprising a multilayer 1120 consisting of two Al.sub.2O.sub.3 layers 1121b, and two Ta.sub.2O.sub.5 layers 1121a, and a (SiO.sub.2) main sol-gel coating 130.

[0172] FIGS. 5a-5b show some experimental results. In the figures, coated luminescent particles 100 of the invention (here comprising SrLiAl.sub.3N.sub.4:Eu) are compared to corresponding prior art luminescent particles. The prior art luminescent particles also comprise an ALD coating layer and a sol-gel coating layer. However, the sol-gel coating layer is configured directly at the surface of the luminescent core 102, and the ALD coating layer is configured onto the sol-gel coating.

[0173] In FIG. 5a. the (normalized) light output (Y-axis) over time, especially hours (X-axis) of the respective luminescent particles in silicone is given. During the experiment, the particles were kept at 130° C. and 100% relative humidity. The circular markers indicate the luminescent particle 100 of the invention; the square markers indicate the prior art luminescent particle.

[0174] In FIG. 5b. the failure probability of white LEDs with the respective luminescent particles is given after maintaining the respective LEDs over 500 hours at 85° C. and 85% relative humidity. The square markers indicate the luminescent particle 100 of the invention; the circular markers indicate the prior art luminescent particle. Note that the probability is given in percentages at the Y-axis in a logarithmical scale. The color point shift in Δu′v′ (sometimes also indicated as “(du′v′)” or “duv”) is given at the X-axis. The (LEDs comprising the) luminescent particles 100 of the invention clearly show less color shift (Δu′v′ is calculated as the Euclidian distance between a pair of chromaticity coordinates in the (u′, v′) CIE 1976 color space).

[0175] Hence, this invention concerns methods to improve the barrier properties of phosphor particle coatings. While the invention is generally applicable to various phosphor particles, it is particularly suitable for nitride based narrow-band, red-emitting phosphors like nitride aluminates or oxo nitride aluminates due to their high sensitivity against moisture.

[0176] FIGS. 6A-6B show, respectively, cross-sectional and top views of an array 600 of pcLEDs 610, which pcLEDs 610 may be structured as lighting device 20, as shown in FIG. 3, that include a wavelength converter 30 comprising the coated luminescent particles 100 as defined herein included in phosphor pixels 606 with semiconductor diode 612 disposed on a substrate 602. Such an array may include any suitable number of pcLEDs arranged in any suitable manner. In the illustrated example the array is depicted as formed monolithically on a shared substrate, but alternatively an array of pcLEDs may be formed from separate individual pcLEDs. Substrate 602 may optionally comprise CMOS circuitry for driving the LED and may be formed from any suitable materials.

[0177] Although FIGS. 6A-6B, show a three-by-three array of nine pcLEDs, such arrays may include for example tens, hundreds, or thousands of LEDs. Individual LEDs (pixels) may have widths (e.g., side lengths) in the plane of the array, for example, less than or equal to 1 millimeter (mm), less than or equal to 500 microns, less than or equal to 100 microns, or less than or equal to 50 microns. LEDs in such an array may be spaced apart from each other by streets or lanes having a width in the plane of the array of, for example, hundreds of microns, less than or equal to 100 microns, less than or equal to 50 microns, less than or equal to 10 microns, or less than or equal to 5 microns. Although the illustrated examples show rectangular pixels arranged in a symmetric matrix, the pixels and the array may have any suitable shape or arrangement.

[0178] LEDs having dimensions in the plane of the array (e.g., side lengths) of less than or equal to about 50 microns are typically referred to as microLEDs, and an array of such microLEDs may be referred to as a microLED array.

[0179] An array of LEDs, or portions of such an array, may be formed as a segmented monolithic structure in which individual LED pixels are electrically isolated from each other by trenches and/or insulating material, but the electrically isolated segments remain physically connected to each other by portions of the semiconductor structure.

[0180] The individual LEDs in an LED array may be individually addressable, may be addressable as part of a group or subset of the pixels in the array, or may not be addressable. Thus, light emitting pixel arrays are useful for any application requiring or benefiting from fine-grained intensity, spatial, and temporal control of light distribution. These applications may include, but are not limited to, precise special patterning of emitted light from pixel blocks or individual pixels. Depending on the application, emitted light may be spectrally distinct, adaptive over time, and/or environmentally responsive. Such light emitting pixel arrays may provide pre-programmed light distribution in various intensity, spatial, or temporal patterns. The emitted light may be based at least in part on received sensor data and may be used for optical wireless communications. Associated electronics and optics may be distinct at a pixel, pixel block, or device level.

[0181] As shown in FIGS. 7A-7B, a pcLED array 600 may be mounted on an electronics board 700 comprising a power and control module 702, a sensor module 704, and an LED attach region 706. Power and control module 702 may receive power and control signals from external sources and signals from sensor module 704, based on which power and control module 702 controls operation of the LEDs. Sensor module 704 may receive signals from any suitable sensors, for example from temperature or light sensors. Alternatively, pcLED array 600 may be mounted on a separate board (not shown) from the power and control module and the sensor module.

[0182] Individual pcLEDs may optionally incorporate or be arranged in combination with a lens or other optical element located adjacent to or disposed on the phosphor layer. Such an optical element, not shown in the figures, may be referred to as a “primary optical element”. In addition, as shown in FIGS. 8A-8B a pcLED array 600 (for example, mounted on an electronics board 700) may be arranged in combination with secondary optical elements such as waveguides, lenses, or both for use in an intended application. In FIG. 8A, light emitted by pcLEDs 610 is collected by waveguides 802 and directed to projection lens 804. Projection lens 804 may be a Fresnel lens, for example. This arrangement may be suitable for use, for example, in automobile headlights. In FIG. 8B, light emitted by pcLEDs 610 is collected directly by projection lens 804 without use of intervening waveguides. This arrangement may be particularly suitable when pcLEDs can be spaced sufficiently close to each other and may also be used in automobile headlights as well as in camera flash applications. A microLED display application may use similar optical arrangements to those depicted in FIGS. 8A-8B, for example. Generally, any suitable arrangement of optical elements may be used in combination with the LED arrays described herein, depending on the desired application.

[0183] An array of independently operable LEDs may be used in combination with a lens, lens system, or other optical system (e.g., as described above) to provide illumination that is adaptable for a particular purpose. For example, in operation such an adaptive lighting system may provide illumination that varies by color and/or intensity across an illuminated scene or object and/or is aimed in a desired direction. A controller can be configured to receive data indicating locations and color characteristics of objects or persons in a scene and based on that information control LEDs in an LED array to provide illumination adapted to the scene. Such data can be provided for example by an image sensor, or optical (e.g. laser scanning) or non-optical (e.g. millimeter radar) sensors. Such adaptive illumination is increasingly important for automotive, mobile device camera, VR, and AR applications.

[0184] FIG. 9 schematically illustrates an example camera flash system 900 comprising an LED array and lens system 902, which may be similar or identical to the systems described above. Flash system 900 also comprises an LED driver 906 that is controlled by a controller 904, such as a microprocessor. Controller 904 may also be coupled to a camera 907 and to sensors 908, and operate in accordance with instructions and profiles stored in memory 910. Camera 907 and adaptive illumination system 902 may be controlled by controller 904 to match their fields of view.

[0185] Sensors 908 may include, for example, positional sensors (e.g., a gyroscope and/or accelerometer) and/or other sensors that may be used to determine the position, speed, and orientation of system 900. The signals from the sensors 908 may be supplied to the controller 904 to be used to determine the appropriate course of action of the controller 904 (e.g., which LEDs are currently illuminating a target and which LEDs will be illuminating the target a predetermined amount of time later).

[0186] In operation, illumination from some or all pixels of the LED array in 902 may be adjusted—deactivated, operated at full intensity, or operated at an intermediate intensity. Beam focus or steering of light emitted by the LED array in 902 can be performed electronically by activating one or more subsets of the pixels, to permit dynamic adjustment of the beam shape without moving optics or changing the focus of the lens in the lighting apparatus.

[0187] FIG. 10 schematically illustrates an example display (e.g., AR/VR/MR) system 1000 that includes an adaptive light emitting array 1010, display 1020, a light emitting array controller 1030, sensor system 1040, and system controller 1050. Control input is provided to the sensor system 1040, while power and user data input is provided to the system controller 1050. In some embodiments modules included in system 1000 can be compactly arranged in a single structure, or one or more elements can be separately mounted and connected via wireless or wired communication. For example, the light emitting array 1010, display 1020, and sensor system 1040 can be mounted on a headset or glasses, with the light emitting controller and/or system controller 1050 separately mounted.

[0188] The light emitting array 1010 may include one or more adaptive light emitting arrays, as described above, for example, that can be used to project light in graphical or object patterns that can support AR/VR/MR systems. In some embodiments, arrays of microLEDs can be used.

[0189] System 1000 can incorporate a wide range of optics in adaptive light emitting array 1010 and/or display 1020, for example to couple light emitted by adaptive light emitting array 1010 into display 1020.

[0190] Sensor system 1040 can include, for example, external sensors such as cameras, depth sensors, or audio sensors that monitor the environment, and internal sensors such as accelerometers or two or three axis gyroscopes that monitor an AR/VR/MR headset position. Other sensors can include but are not limited to air pressure, stress sensors, temperature sensors, or any other suitable sensors needed for local or remote environmental monitoring. In some embodiments, control input can include detected touch or taps, gestural input, or control based on headset or display position.

[0191] In response to data from sensor system 1040, system controller 1050 can send images or instructions to the light emitting array controller 1030. Changes or modification to the images or instructions can also be made by user data input, or automated data input as needed. User data input can include but is not limited to that provided by audio instructions, haptic feedback, eye or pupil positioning, or connected keyboard, mouse, or game controller.

[0192] In an embodiment, the invention provides a wet chemical washing (including drying) process of the powder phosphor (the luminescent core(s)) to form an oxide outer particle layer. Further a primary (SiO.sub.2) sol-gel layer may be deposited by a (primary) sol-gel process to provide the primary sol-gel layer with a thickness in the range of 0.5-5 nm. Next, a multilayer may be deposited by ALD with a total ALD coating layer thickness d2 in embodiments of 20-50 nm and a (sub)layer thickness d21 of the layers 1121 of the multilayer 1120 in the range of 1-20 nm. The multilayer 1120 is especially comprised of two or more metal oxides such as Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, HfO.sub.2, SnO.sub.2, ZnO, Ta.sub.2O.sub.5. Next, a third layer, especially a main sol-gel coating layer 130, e.g. of SiO.sub.2 may be deposited by a (main) sol-gel process with a thickness in the range of 100-500 nm. In yet further embodiments, a fourth layer 140 may be deposited by a further ALD process. The further ALD coating layer 140 may in embodiments have a total thickness d4 of 5-50 nm and especially may comprise a multilayer with sub-layer thickness in the range of 1-20 nm. The multilayer is in embodiments comprised of one or more metal oxides, such as Al.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, HfO.sub.2, SnO.sub.2, ZnO, Ta.sub.2O.sub.5.

EXPERIMENTAL

[0193] The effect of the new coating architecture of the invention was tested by forming a luminescent particle with a hybrid coating as disclosed herein:

Polyol Washing Process:

10.3 g of a Raw Phosphor Powder Sample of Composition

[0194] Sr.sub.0.995Li.sub.2Al.sub.1.995Si.sub.0.005O.sub.1.995N.sub.2.005:Eu.sub.0.005 was mixed 30.0 g ethanol and 30.0 g triethylene glycol with the suspension showing a total water content in the 0.05-0.1% range in an ultrasonic bath followed by a 16 hr treatment at 80° C. in a closed pressure vessel. After cooling down to room temperature, the phosphor powder was washed with ethanol and dried at 100° C. under ambient atmosphere.

Mixed Solvent Acetic Acid Washing Process:

[0195] 200-250 g of SrLiAl.sub.3N.sub.4:Eu.sub.0.007 were stirred in 837 g isopropanol. 560 g of 18.5 wt % acetic acid were slowly added under stirring. The suspension was further stirred until a total time of 40 min (including acid addition) passed. After 30 min sedimentation the supernatant was largely removed by decantation followed by filtration and rinsing with acetic acid/isopropanol mixture and isopropanol. The washed phosphor is finally dried at 50° C. in vacuum overnight.

Thin Amorphous Silica Layer (<5 nm)

[0196] In this experiment a primary sol-gel coating layer was provided. 200 g phosphor powder (typically after washing) were stirred in 960 g ethanol. To this suspension 3.5 g tetraethyl orthosilicate were added and stirred for 10 min under sonication. 90 g 25 wt % aqueous ammonia solution were added and stirring under sonication is continued for another 20 min. Fine particles including nanosized silica particles formed as by-product were removed by threefold sedimentation in ethanol and decantation. The coated powder was dried at 50° C. in vacuum overnight. After dry-sieving (mesh size 100 μm) the coating was cured by heating the powder to 300° C. for 10 hr. under vacuum.

ALD Nanolaminate (˜25 nm)

[0197] Next, a main ALD coating layer comprising an ALD nanolaminate was applied on primer layer comprising phosphor particles (comprising SrLiAl.sub.3N.sub.4:Eu) in a Picosun Oy ALD R200 reactor. Precursor materials were trimethylaluminum and H.sub.2O to form an Al.sub.2O.sub.3 film and (tert-Butylimido)tris(ethylmethylamino) tantalum (V) and H.sub.2O to form a Ta.sub.2O.sub.5 film. The deposition temperature was set to 250° C. The purge time of nitrogen gas in between precursor pulses was 60 seconds. The nanolaminate consists of 2×Al.sub.2O.sub.3/Ta.sub.2O.sub.5 sublayers with a total thickness of around 25 nm.

Thick Amorphous Silica Layer (˜170 nm)

[0198] In this experiment a main sol-gel coating layer was provided on the luminescent particle. 85 g powder (typically after ALD coating) were stirred in 672 g ethanol for 15 min under sonication. To this suspension 1) 116 g 25 wt % aqueous ammonia solution were added fast (<30 s) and 2) a solution of 68 g tetraethyl orthosilicate in 408 g ethanol is added drop-wise (˜45 min). After the addition of alkoxide precursor was finished, the suspension was stirred for another 30 min without sonication.

[0199] Fine particles including sub-micron sized silica particles formed as by-product were removed by threefold sedimentation in ethanol and decantation. The coated powder was dried at 50° C. in vacuum overnight. After dry-sieving (mesh size 63 μm) the coating was cured by heating the powder to 300° C. for 10 hr. under vacuum.

[0200] A SEM image of some of the particles is given in FIG. 4a. A TEM image of the particles is given in FIG. 4b.

Comparison Test

[0201] The prepared particles in silicone were subjected to a stress test and compared with a control particles i.e. particles comprising a prior art coating architecture. In the prior art coating architecture the luminescent particle is initially coated with a relatively thick sol-gel coating and successively with a thin ALD coating. In the stress test, the light output was measured over time while keeping the particles at a temperature of 130° C. and 100% relative humidity.

[0202] The prepared particles were further applied in a white LED and stressed over 500 hours at 85° C. and 85% relative humidity. The failure probability of the white LEDs with the luminescent particles according to the invention was compared to the failure probability of white LEDs comprising the prior art coating architecture subjected to the same stress test (the control LED).

[0203] The results are depicted in FIGS. 5a-5b showing a significantly improved reduction in light output after 60 hours stress test, i.e. less than 5% compared to a reduction of more than 50% for the control particles. Also the color shift (Δu′v′) is substantially minimized compared to the control LED.

[0204] The term “plurality” refers to two or more.

[0205] The terms “substantially” or “essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms “substantially” or “essentially” may also include embodiments with “entirely”, “completely”, “all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term “essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%.

[0206] The term “comprise” also includes embodiments wherein the term “comprises” means “consists of”.

[0207] The term “and/or” especially relates to one or more of the items mentioned before and after “and/or”. For instance, a phrase “item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term “comprising” may in an embodiment refer to “consisting of” but may in another embodiment also refer to “containing at least the defined species and optionally one or more other species”.

[0208] Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

[0209] The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation.

[0210] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

[0211] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

[0212] Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[0213] The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

[0214] The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0215] The invention also provides a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system.

[0216] The invention further applies to a device, apparatus, or system comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

[0217] The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.