The influence of phosphate concentration on the spectral properties of thulium ions in fluorophosphate glasses

The Judd–Ofelt parameters of thulium ions in fluorophosphate glasses with different phosphate component concentrations are calculated. It is shown that the $\Omega_t$ parameters of glasses with Ba(PO$_{3})_{2}$ concentrations up to 10 mol % are close to the corresponding parameters of fluoride glasses and sharply increase with increasing phosphate concentration. The spectral-luminescent parameters of glasses are analyzed within the Judd–Ofelt theory. The spontaneous transition probabilities, branching ratios ($\beta$), and radiative lifetimes $(\tau_{\operatorname{rad}})$ for different excited states of Tm$^{3+}$ are determined. It is found that glasses with low phosphate concentrations are characterized by a high radiative lifetime of the excited $^{3}F_{4}$ laser level. It is shown that the glasses under study have a typical broad flat gain spectrum, which makes them promising for developing broadband amplifiers.