Structural properties and luminescence of rare earth ions in transition metal fluoride glasses

The fluorescence of rare-earth ions RE3+ = Pr3+, Er3+ and Tm3+ has been compared in the transition-metal fluoride glass (36 mol% PbF2-24 mol% ZnF2-35 mol% GaF3-5 mol% YF3-2Al mol% F-3) doped with either REF3 or RECl3. For the phonon-sensitive radiative transition, the lifetime is prolonged at low RECl3 concentrations because the phonon energy and/or electron coupling are reduced. For Pr3+, the doping with PrCl3 increases the lifetime by 50% with respect to PrF3 doping. These results suggest that the Cl- ions remain in the coordination sphere of the RE3+ ions in the ReCl3-doped glass after melting.