Low melting temperature bismuth-doped tin phosphate glass

We fabricated Bi-doped tin phosphate glasses using SnO, phosphoric acid, and Bi 2 O 3 at melting temperatures between 550° and 1100°C. In undoped glasses, the Tauc bandgap increases with melting temperature, which is attributed to a higher fraction of bridging oxygens in PO 4 units. Doping with 0.2 mol% Bi 2 O 3 introduces characteristic absorption bands at 360 and 540 nm and dramatically increases the background absorption of the base glass, especially at higher melting temperatures, due to phase separation and the formation of SnO and SnO 2 nanocrystals, as confirmed by Raman spectroscopy. Under green excitation, a broad NIR photoluminescence (PL) band centered at 1180 nm, with a full width at half maximum of 200 to 300 nm, is observed. PL decay shows short (∼10µs) and long (∼100µs) lifetime components, both varying with melting temperature and PL wavelength. The lowest melting temperature glass exhibits significantly shorter lifetimes, indicating enhanced non-radiative decay and reduced quantum efficiency. Although the nature and formation mechanism of the optically active Bi center in Bi-doped glasses remain unknown, our 550°C glass defines a new low-temperature threshold for its thermal activation in oxide glasses and provides a feasible platform for in situ optical and X-ray studies of its formation mechanism during glass melting.