Luminescence and upconversion processes in Er3+-doped tellurite glasses

This work presents a spectroscopic investigation of tellurite glasses with the composition 65TeO2-15Li2O-20ZnO doped with different concentrations of Er2O3. Optical absorption and emission spectroscopy were performed at room temperature to determine emission properties of Er3+ in the visible and near-infrared regions. The samples presented intense green emission due to the H11/22→I15/24 and S3/24→I15/24 transitions. Emission intensities at 992 and 1550 nm exhibit a relative increase with increasing doping concentration. Luminescence decay curves for the S3/24→I15/24 transition follows a non-exponential behavior, while the I11/24→I15/24 and I13/24→I15/24 transitions presented simple exponential behavior with high lifetime values. Under 975 nm excitation, upconversion luminescences in the green and red regions are observed, with a relative increase for red emission as function of doping concentration. The possible mechanisms considering multi-phonon relaxation, energy transfer and cross-relaxation processes were discussed for green and red emissions under excitations at 488 and 975 nm. The square dependence of green emission on the excitation power indicates two photons contribution to the upconversion emission. The full width at half-maximum values of emission at 1550 nm increased with increasing Er3+ concentration, showing the potential of the studied material as infrared amplifier.