Luminescence Characteristics and Energy Transfer of Tm3+-Doped Calcium Fluoroborate Glasses for Fiber Amplifiers

Abstract

The conventional melt quenching method was employed to fabricate calcium fluoroborate glasses doped with Tm2O3 (CFBTm). Optical absorption and photoluminescence spectra were recorded in the UV, Vis, and NIR wavelength ranges. Judd-Ofelt (J-O) and free-ion parameters were computed based on the absorption band intensities and energy level positions. Utilizing the J-O parameters, various radiative parameters were determined for distinct excited states of Tm3+ ions in CFB glasses. Stimulated emission cross-sections (se) and effective bandwidths (Dleff) were calculated for the observed emission bands. The increase in Tm2O3 concentration resulted in an augmentation of emission peak intensities in the visible range, followed by a decline at higher concentrations. The quenching of emission intensities was attributed to energy transfer through cross-relaxation mechanisms. The NIR emission spectrum, excited by an 808 nm laser diode (LD), exhibited a peak at 1.47 mm corresponding to the 3H4-3F4 transition, with the intensity of the NIR emission peak increasing with the concentration of Tm2O3. Furthermore, Beer-Lambert and McCumber theories were applied to assess the absorption and emission cross-sections for the prominent 3F4–3H6 transition at the 1.82 mm emission wavelength.