To modify the luminescence properties of Ce³⁺-doped Y₃Al₅O₁₂ (YAG) phosphors, they have been coated with a carbon layer by chemical vapor deposition and subsequently heat-treated at high temperature under N₂ atmosphere. Luminescence of the carbon coated YAG:Ce³⁺ phosphors has been investigated as a function of heat-treatment at 1500 and 1650 °C. The 540 nm emission intensity of C@YAG:Ce³⁺ is the highest when heated at 1650 °C, while a blue emission at 400-420 nm is observed when heated at 1500 °C but not at 1650 °C. It is verified by X-ray diffraction (XRD) that the intriguing luminescence changes are induced by the formation of new phases in C@YAG:Ce³⁺-1500 °C, which disappear in C@YAG:Ce³⁺-1650 °C. In order to understand the mechanisms responsible for the enhancement of YAG:Ce³⁺ emission and the presence of the blue emission observed for C@YAG:Ce³⁺ -1500 °C, the samples have been investigated by a combination of several electron microscopy techniques, such as HRTEM, SEM-CL, and SEM-EDS. This local and cross-sectional analysis clearly reveals a gradual transformation of phase and morphology in heated C@YAG:Ce³⁺ phosphors, which is related to a reaction between C and YAG:Ce³⁺ in N₂ atmosphere. Through reaction between the carbon layer and YAG host materials, the emission colour of the phosphors can be modified from yellow, white, and then back to yellow under UV excitation as a function of heat-treatment in N₂ atmosphere.

The β-sialon:Eu²⁺ phosphor has superior luminescent properties as an excellent green down-conversion material for white light-emitting diodes. To take advantage of its high chromaticity and apply it to field emission displays (FEDs), the drawback of its electron insulation that impedes the electron transmission when excited by e-beam needs to be solved. In this work, a facile method was adopted to coat conductive In₂O₃ on the surface of β-sialon:Eu²⁺ phosphor, and the influence of In₂O₃ coating on the cathodoluminescent properties was investigated. The results show that the In₂O₃ coating contributes to charge elimination and significantly improves the cathodoluminescence (CL) of β-sialon:Eu²⁺. Under 19 kV/1.0 nA e-beam excitation, the In₂O₃ coated sample shows CL intensity about four times higher than that of the uncoated β-sialon:Eu²⁺. Moreover, no luminescence saturation occurs in coated β-sialon:Eu²⁺, indicating that the In₂O₃-coated β-sialon:Eu²⁺ would be a promising green emissive material for full-color FEDs.