Improved performance by plasma-treated silicate phosphor particles with a sol–gel derived protective coating of indium oxide

• A uniform In2O3 coating layer can be achieved using sol–gel process.
• After plasma treatment, In2O3 layer had thicker and smoother.
• In2O3-coated phosphor, when applied to pc-LEDs showed a small decrease in optical output.

The optical properties and reliability of silicate phosphor was fairly improved by an amorphous In2O3 protective coating on plasma-treated phosphor particles. The In2O3 layers were coated using a conventional sol–gel method with alkoxide precursor in N2 gas. The surface morphology of silicate particles was smoother after Ar-plasma surface modification. When plasma surface treatment of the phosphor was applied before sol–gel coating, the In2O3 coating was almost 3-times thicker, and the surface of the phosphor particles was smoother, than could be obtained when sol–gel coating was not preceded by plasma treatment. This was because the treatment caused the surface to become hydrophilic. The light absorption rate and quantum efficiency were increased from 75.3% and 93.8%, to 79.2% and 95.7%, after plasma-treated In2O3 coating. Bare silicate phosphor used in 450-nm vertical-type LEDs, displayed 10% decreased optical output, whereas In2O3-coated phosphor showed just 3% decreased optical output after 1000 h of input current at 350 mA; under conditions of high humidity and high temperature.

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