Laterally heterogenous wavelength-converting layer
A laterally heterogenous wavelength-converting optical element includes pixel regions surrounded by border regions; each includes down-converting phosphor particles bound by a coating or solid medium. The pixel regions are aligned with LEDs of an array. The phosphor regions differ with respect to one or more of compositions, particle sizes, coating thicknesses, refractive indices, or voids (size, number density, or volume fraction). Those difference(s) can result in the border regions exhibiting larger optical scattering, which can improve contrast of down-converted light emitted by adjacent pixels of the array.
1. A light-emitting device comprising:
a wavelength-converting optical element; and
an array comprising a plurality of microLEDs and non-light-emitting areas separating adjacent microLEDs,
wherein the wavelength-converting optical element is arranged as a solid wavelength-converting layer disposed on the array and comprises:
a plurality of first regions aligned with the plurality of microLEDs and comprising phosphor particles of a first characteristic size dispersed in, or bound together with, a first transparent material; and
a second region contiguous with the first regions, aligned with the non-light-emitting areas, and comprising phosphor particles of a second characteristic size dispersed in, or bound together with, a second transparent material, wherein the second region exhibits optical scattering greater than optical scattering exhibited by the first regions.
2. The light-emitting device of claim 1 , wherein the first characteristic size differs from the second characteristic size.
3. The light-emitting device of claim 1 , wherein the second characteristic size is less than 50% of the first characteristic size.
4. The light-emitting device of claim 1 , wherein the first characteristic size is less than 10 μm, or the second characteristic size is less than 5 μm.
5. The light-emitting device of claim 1 , wherein spacing of the microLEDs of the array is less than 0.10 mm, or width of the non-light-emitting areas separating adjacent microLEDs of the array is less than 0.010 mm.
6. The light-emitting device of claim 1 , wherein: (i) the first regions comprise the phosphor particles of the first characteristic size embedded in the first transparent material, the first transparent material forming a first solid medium, and (ii) the second region comprises the phosphor particles of the second characteristic size embedded in the second transparent material, the second transparent material forming a second solid medium.
7. The light-emitting device of claim 6 , wherein the first regions differ from the second region with respect to compositions or refractive indices characterizing the first solid medium and the second solid medium.
8. The light-emitting device of claim 6 further comprising scattering particles embedded in the second solid medium.
9. The light-emitting device of claim 6 , wherein the first solid medium includes one or more polymers, or the second solid medium includes one or more polymers.
10. The light-emitting device of claim 6 , wherein the first solid medium includes one or more silicones, and the second solid medium includes one or more silicones.
11. The light-emitting device of claim 6 , wherein the first and second solid media have the same material composition.
12. The light-emitting device of claim 1 , wherein: (i) the first regions comprise the phosphor particles of the first characteristic size and a first coating on the phosphor particles of the first regions that binds together the phosphor particles of the first regions, the first coating comprising the first transparent material, and (ii) the second region comprises the phosphor particles of the second characteristic size and a second coating on the phosphor particles of the second region that binds together the phosphor particles of the second region, the second coating comprising the second transparent material.
13. The light-emitting device of claim 12 , wherein the first regions differ from the second region with respect to size, number density, or volume fraction characterizing voids among the phosphor particles of the first regions and voids among the phosphor particles of the second region.
14. The light-emitting device of claim 12 , wherein the first regions differ from the second region with respect to thicknesses, compositions, or refractive indices characterizing the first coating and the second coating.
15. The light-emitting device of claim 12 , wherein the first coating has a thickness greater than 0.20 μm, or the second coating has a non-zero thickness less than 0.10 μm.
16. The light-emitting device of claim 12 , wherein the first coating includes one or more metal or semiconductor oxides, and the second coating includes one or more metal or semiconductor oxides.
17. The light-emitting device of claim 12 , wherein the first and second coatings have the same material composition.
18. The light-emitting device of claim 12 , wherein the first coating or the second coating includes one or more materials compatible with formation using an atomic layer deposition (ALD) process or using a conformal chemical vapor deposition (CVD) process.
19. The light-emitting device of claim 12 , wherein: (i) the second coating has a characteristic thickness that is less than 50% of a characteristic thickness of the first coating, or (ii) number density or volume fraction of voids among the phosphor particles of the first regions is less than 50% of number density or volume fraction of voids among the phosphor particles of the second region.
20. The light-emitting device of claim 1 , wherein the first regions exhibit a contrast ratio for down-converted light exiting the wavelength-converting layer from adjacent first regions thereof that is greater than 5:1, the down-converted light resulting from absorption of light emitted by the microLEDs and subsequent emission of the down-converted light at a wavelength longer than a wavelength of the light emitted by the microLEDs.