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

Abstract The optical properties and reliability of silicate phosphor was fairly improved by an amorphous In 2 O 3 protective coating on plasma-treated phosphor particles. The In 2 O 3 layers were coated using a conventional sol–gel method with alkoxide precursor in N 2 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 In 2 O 3 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 In 2 O 3 coating. Bare silicate phosphor used in 450-nm vertical-type LEDs, displayed 10% decreased optical output, whereas In 2 O 3 -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.