Synthesis and photoluminescence of Ca–(Sn,Ti)–Si–O compounds

The phase relation of the compounds prepared in the CaO–SnO2–SiO2 system at 1673 K and in the CaO–TiO2–SiO2 system at 1573 K was investigated in order to explore new Ti4+-activated stannate phosphors. Solid solutions of Ca(Sn1−xTix)SiO5 and Ca3(Sn1−yTiy)Si2O9 were synthesized at x = 0–1.0 and y = 0–0.10, respectively, and their crystal structures were analyzed by powder X-ray diffraction. Photoluminescence of these solid solutions was observed in a broad range of a visible light wavelength region under ultraviolet (UV) light excitation. The peaks of the emission band of Ca(Sn0.97Ti0.03)SiO5 and Ca3(Sn0.925Ti0.075)Si2O9 were at 510 nm under excitation of 252 nm and at 534 nm under excitation of 258 nm, respectively. The absorption edges estimated by the diffuse reflectance spectra were at 300 nm (4.1 eV) for CaSnSiO5 and at 270 nm (4.6 eV) for Ca3SnSi2O9, suggesting that the excitation levels in Ca(Sn1−xTix)SiO5 were above the band gap of the host, although the levels in Ca3(Sn1−yTiy)Si2O9 were within the band gap and near the conduction band edge.