PHOSPHOR LAYER WITH ADDITIONAL PARTICLES
A phosphor layer includes phosphor particles and small typically non-luminescent particles, such as nanoparticles. The small particles improve adherence, coherence, and homogeneity of the phosphor layer by accumulating at contact points of the phosphor particles. Their diameter is smaller than those of the phosphor particles. The small particles may be co-deposited with the phosphor particles during electrophoretic deposition, increasing the formulation conductivity during deposition to increase transport speed. The small particles may be catalysts that aid in removal of organic material included in the electrophoretic deposition process.
1 . A method comprising:
providing a surface and a formulation in contact with the surface, the formulation comprising phosphor particles and small particles;
co-depositing the phosphor particles and the small particles on the surface by electrophoretic deposition (EPD) to form a phosphor layer.
2 . The method of claim 1 , wherein the surface is a surface of a light emitting device.
3 . The method of claim 1 , wherein the formulation further comprises charging agents physically bound to the phosphor particles, and depositing the phosphor particles and the small particles further comprises depositing the charging agents with the phosphor particles and small particles to form the phosphor layer.
4 . The method of claim 1 , wherein the charging agent is Cr-anthralinate.
5 . The method of claim 1 , wherein the formulation further comprises polymers, and depositing the phosphor particles and the small particles further comprises depositing the polymers with the phosphor particles and the small particles to form the phosphor layer.
6 . The method of claim 1 , wherein the polymer is polyalkylmethacrylate (PAMA).
7 . The method of claim 5 , further comprising, after depositing the phosphor particles and the small particles, removing the charging agent and the polymer from the phosphor layer.
8 . The method of claim 7 , wherein removing the charging agent and the polymer comprises irradiating the phosphor layer with UV light.
9 . The method of claim 7 , wherein the small particles in the phosphor layer catalyze the removing the charging agent and the polymer.
10 . The method of claim 1 , further comprising, after depositing the phosphor particles, rinsing the phosphor layer.
11 . The method of claim 10 , further comprising, after rinsing the phosphor layer, depositing by atomic layer deposition (ALD) an ALD layer on the phosphor layer.
12 . The method of claim 11 , wherein the ALD layer is a different material from the small particles.
13 . The method of claim 12 , wherein the phosphor particles have diameters at least ten times larger than those of the small particles.
14 . The method of claim 13 , wherein the formulation has a conductivity in the range of 8 to 100 picoSiemens/cm.
15 . A light emitting device, comprising:
a light emitting diode having a light emitting surface;
a phosphor layer on the light emitting surface, the phosphor layer comprising:
phosphor particles each having a first diameter from 2 to 10 microns; and
small particles each having a second diameter of 20% or less than the first diameter of the phosphor particles and comprising a first material of at least one of HfO 2 , Ta 2 O 5 , TiO 2 , and CeO 2 ; and
an atomic layer deposition (ALD) layer comprising the first material.
16 . The light emitting device of claim 15 , wherein the ALD layer has a thickness of 100 nm or less on the phosphor layer.
17 . The light emitting device of claim 16 , wherein the small particles each have a diameter at or below 300 nm.
18 . The light emitting device of claim 15 , wherein the nanoparticle is titanium oxide or cerium oxide.
19 . The light emitting device of claim 18 , wherein the nanoparticle is cerium oxide.
20 . The light emitting device of claim 15 , wherein the light emitting surface is not a flat plane and the phosphor layer is conformal on the light emitting surface.