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(Sn_1−xTi_x)SiO₅ and Ca₃(Sn_1−yTi_y)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(Sn_0.97Ti_0.03)SiO₅ and Ca₃(Sn_0.925Ti_0.075)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(Sn_1−xTi_x)SiO₅ were above the band gap of the host, although the levels in Ca₃(Sn_1−yTi_y)Si₂O₉ were within the band gap and near the conduction band edge.