Energy transfer and luminescence properties of Tm3+ ions in calcium fluoroborate glasses for fiber amplifiers

Calcium fluoroborate glasses doped with Tm2O3 (CFBTm) were prepared by the conventional melt quenching method. Optical absorption and the photoluminescence spectra were recorded in UV–vis–NIR regions. Free-ion and Judd–Ofelt (J–O) parameters have been evaluated from the energy level positions and the intensities of the absorption bands. Using the J–O parameters, several radiative parameters were calculated for different excited states of Tm3+ ions in CFB glasses. Stimulated emission cross-sections (σe) and effective bandwidths (Δλeff) were determined for the observed emission bands. The intensities of the emission peaks in the visible region increase with the increase of Tm2O3 concentration and then decrease at higher concentrations. The quenching of emission intensities has been attributed to the energy transfer through cross-relaxation mechanisms. The NIR emission spectrum recorded with the excitation of 808 nm laser diode (LD) exhibited an emission peak at 1.47 μm corresponding to the 3H4→3F4 transition. The intensity of NIR emission peak increases with increase of Tm2O3 concentration. Beer Lambert and McCumber theories were also implemented to evaluate the absorption and emission cross-sections for the prominent 3F4→3H6 transition at 1.82 μm emission wavelength.