Fabrication of TiO₂–SiO₂ glasses containing Ca-α-SiAlON:Eu²⁺ phosphor using the sol–gel process

抄録

We prepared titanosilicate glasses by the sol–gel method and studied its ability to disperse Ca-α-SiAlON:Eu²⁺ phosphor, which is a typical yellow phosphor and applicable for white light-emitting diodes (LEDs). xTiO₂–(100 − x)SiO₂ glasses dispersed with SiAlON powders were obtained by sintering at 900°C with x ranging from 10 to 30; the glasses changed to black after sintering at 1000°C. Diffuse reflectance spectra suggested that the colorization was caused by the formation of Ti³⁺ ions in the samples. The local structures of Ti and Eu were measured by X-ray absorption fine structure spectroscopy. Ti K-edge spectra showed that the local structure of Ti was 5-coordinated in the glass where x = 10 and 6-coordinated in the glass where x = 30. Eu L_III-edge spectra indicated that both Eu²⁺ and Eu³⁺ were present and the ratio of Eu²⁺ to Eu³⁺ depended on the heating temperature. The reduction atmosphere might affect the colorization of the glasses sintered at 1000°C. The quantum efficiencies (QE) of the glasses sintered at 900°C were estimated and that of the glass with x = 10 was the highest among of the samples, higher than that of the SiAlON powders. It is suggested from the measurement of refractive index and XRD patterns that the improvement in QE is caused by the decrease in the light scattering at the interface between the phosphor and the glasses due to differences in refractive indices and the formation of crystals.