Optical Absorption and NIR Photoluminescence of Nd³⁺-Activated Strontium Phosphate Glasses

Abstract

Strontium phosphate glasses with various concentrations of Nd₂O₃ have been prepared by melt quenching method. Absorption and photoluminescence spectra and lifetime measurements have been carried out to obtain the optical properties of these glasses. From the absorption spectrum, intensity and radiative parameters have been evaluated using Judd–Ofelt analysis. Near-infrared photoluminescence spectra consist of three bands centered at 875 nm, 1056 nm and 1327 nm, among which the highest intensity has been noticed for the band at 1056 nm that corresponds to the ⁴F_3/2 → ⁴F_11/2 transition of Nd³⁺ ion. Laser parameters such as branching ratio, band width, stimulated emission cross section and gain bandwidth for the ⁴F_3/2 → ⁴F_11/2 transition are found to be 0.52, 28 nm, 2.31 × 10⁻²⁰ cm² and 6.5 × 10⁻²⁶ cm³, respectively. Decay curves of the ⁴F_3/2 level of Nd³⁺ ions exhibit a single exponential nature at lower concentrations, while they become non-exponential at higher concentrations (≥ 0.1 mol.%) due to non-radiative energy transfer processes. This feature is also associated with shortening of lifetime from 307 μs to 82 μs when the Nd³⁺ ion concentration increases from 0.1 mol.% to 4.0 mol.%. The results have been compared with those of barium and magnesium phosphate glasses and commercial glasses. The results suggest that these glasses have potential applications as infrared laser materials at 1.05 μm.