One of the biggest problems in white light-emitting diodes (WLEDs) is the moisture-induced degradation of phosphors. This paper proposes a simple and feasible surface modification method to solve it, whereby a hydrophobic surface layer is developed on the surface of the phosphors. The particular case of orange-red-emitting Sr₂Si₅N₈:Eu²⁺ (SSN) phosphor was investigated. The mechanism to develop the hydrophobic layer involves hydrolysis and polymerization of tetraethylorthosilicate (TEOS) and polydimethylsiloxane (PDMS). The experimental results showed that the surface layer of SSN phosphor was successfully modified to a hydrophobic nanolayer (8 nm) of amorphous silicon dioxide that contains CH₃ groups in the surface. This hydrophobic surface layer gives the modified phosphor superior stability in high-pressure water steam conditions at 150°C.

Many strategies have been adopted to improve thermal degradation of phosphors. Because of the stability and high transmittance of graphene, here we report a novel method of carbon coating on BaMgAl₁₀O₁₇:Eu²⁺ (BAM) phosphor particles through chemical vapor deposition. The chemical composition, microstructure, and luminescence performance of carbon-coated BAM were characterized carefully. This coating can be controlled within 3-10 atomic layers, depending on the reaction time. Because of the decrease of surface defects and the effective weakening effect of oxidizing Eu²⁺ to Eu³⁺ after carbon coating, different layer numbers showed an obvious effect on the optical properties of carbon-coated BAM. Carbon-coated BAM phosphors had higher emission intensity and better oxidation resistance at high temperature than uncoated BAM phosphors. These results indicate that the method of carbon coating on phosphor particles is a promising way to improve the luminescence properties of other phosphors used in lighting and display devices.