Light emitting device with high near-field contrast ratio
A light emitting device includes an LED having a light emitting top surface and sidewalls. A phosphor structure is attached to the light emitting surface of the LED. The phosphor structure has a light emitting top surface facing away from the LED light emitting surface, and sidewalls. A light reflective material is arranged to cover the sidewalls of the LED and the phosphor structure. A light absorptive region is defined in the light reflective material around a perimeter of the light emitting surface of the phosphor structure. The light absorptive region may be spaced apart from the perimeter of the phosphor structure by a gap. The light absorptive region may be formed by ultraviolet laser illumination of the light reflecting material.
1. A method of manufacturing a light emitting device, the method comprising:
attaching to a light emitting diode a phosphor structure having a light emitting first surface, an oppositely positioned second surface, and sidewalls connecting the top and bottom surfaces, the second surface of the phosphor structure attached to a light emitting surface of the light emitting diode;
disposing a light reflective material on the sidewalls of the phosphor structure; and
illuminating an outer surface of the light reflective material with an ultraviolet laser to form in the light reflective material a light absorptive region surrounding a perimeter of the light emitting first surface of the phosphor structure.
2. The method of claim 1 , wherein illuminating an outer surface of the light reflective material with an ultraviolet laser to form the light absorptive region comprises reducing metal oxide particles in the light reflective material to form light absorptive metallic material.
3. The method of claim 2 , wherein the metal oxide particles comprise TiO 2 .
4. The method of claim 3 , wherein the metal oxide particles comprise the TiO 2 coating SiO 2 particles.
5. The method of claim 1 , wherein the light absorptive region is spaced apart from the perimeter of the light emitting first surface of the phosphor structure by at least 30 microns in a plane of the light emitting first surface of the phosphor structure.
6. The method of claim 1 , wherein the light absorptive region has a width in the plane of the light emitting first surface of the phosphor structure of between about 100 microns and about 200 microns.
7. The method of claim 1 , wherein the light absorptive region has a depth of less than 50 microns perpendicular to the outer surface of the light reflective material.
8. The method of claim 1 , wherein the light absorptive region has a depth of between 40 to 80 microns perpendicular to the outer surface of the light reflective material.
9. The method of claim 1 , wherein the laser has a power of 0.60+/−0.02 W and is pulsed at a frequency of 60 KHz.
10. The method of claim 1 , wherein the light reflective material comprises a silicone binder.
11. The method of claim 10 , wherein the light reflective material comprises between 5% and 40% of the silicone binder.
12. The method of claim 1 , wherein the light reflective material comprises Al 2 O 3 .
13. The method of claim 1 , wherein the light reflective material comprises from 20% to 70% TiO 2 .
14. The method of claim 1 , further comprising applying the light reflective material to the sidewalls of the phosphor structure by molding, dispensing, screen printing, spray, or lamination.
15. The method of claim 1 , wherein the light reflective material comprises sol-gel or liquid glass.
16. The method of claim 1 , wherein the light reflective material comprises inorganic nanoparticles, glass particles or glass fibers.
17. The method of claim 1 , wherein the light reflective material comprises an organic binder.
18. The method of claim 1 , wherein the light reflective material comprises a binder, and illuminating the outer surface of the light reflective material removes some of the binder from an illuminated region.
19. The method of claim 18 , wherein illuminating the outer surface of the light reflective material removes all of the binder from the illuminated region.