Bi luminescence in ABiO2Cl (A=Sr, Ba) and BaBiO2Br

Trivalent bismuth luminescence is reported in three Sillen bismuth oxyhalide phases, SrBiO₂Cl, BaBiO₂Cl, and BaBiO₂Br. These compounds exhibit Bi 6s6p→6s² emission under UV and X-ray radiations. At room temperature, BaBiO₂Cl shows the most intense light emission, with spectral and decay properties similar to those found in Bi₄Ge₃O₁₂ (BGO). At low temperatures, each phase show an increase in the photoluminescence intensities and a narrowing of the emission peaks. In contrast to the temperature dependence of BGO, X-ray excited luminescence intensities of all three phases remain relatively constant throughout the temperature range 10-295 K, though much lower than BGO at low temperatures. This result indicates that the Sillen phases undergo less thermal quenching than BGO. The low temperature and room temperature radio-luminescence decay times were determined from pulsed X-ray measurements. At room temperature, SrBiO₂Cl exhibits faster decays than BGO, while BaBiO₂Cl and BaBiO₂Br have decay times similar to BGO.