Atomic-Scale Structure and Optical Properties of Rare-Earth (RE =Pr, Nd, Er) Doped Sodium Ultraphosphate Glasses

The atomic-scale structure of a series of (Re₂O₃)_x(Na₂O)_y(P₂O₅)_1-x-y glasses (Re = Pr, Nd, Er) where 0.005 ≤ x ≤ 0.05 has been characterized via high-energy X-ray diffraction (HEXRD) technique. In addition, Differential Thermal Analysis (DTA), Fourier Transform Infrared (FTIR) spectroscopy, and absorption and emission spectroscopy in visible and near IR ranges have been used to validate HEXRD results. Coordination numbers for P-O, Na-O, O-O, and P-P were found to be independent of the Re₂O₃ content. In contrast, the Re-O coordination number decreases with Re₂O₃ concentration. However, the glass transition temperature increases with increasing Re₂O₃ content. Even at these very low rare earth concentrations, depolymerization of the glasses at Q³ tetrahedral sites was observed. Quantum efficicencies as high as 70% were observed at certain concentrations. Emission spectra of these glasses show that their florescence efficiency decreases with increasing rare-earth content suggesting that concentration quenching of lasing action may be present even at these very low rare earth concentrations.