Time-resolved study of pump-induced refractive index changes in Tb3+-doped phosphate glasses: Discrimination of electronic and thermal contributions

Time-resolved Z-scan measurements were performed in Tb3+-doped Zinc Phosphate (PZABP) glasses. The electronic and thermal contributions to the Z-scan signal were unequivocally discriminated. The electronic component was shown to increase linearly with the Tb3+ concentration in the glasses and explained by the polarizability difference (dap) between excited and ground states of the Tb3+ ions. Open aperture Z-scan measurements indicate the presence of excited state absorption due to a spin-forbidden transition from the metastable (5D4) 4f level of Tb3+ to the 4f75d1 state. The dap value obtained in the PZABP glass matrix is two orders of magnitude smaller than the observed in aluminosilicate glasses, indicating that dap of Tb3+-doped materials is very sensitive to the host crystal field, as compared to other rare-earth ions such as Nd3+ and Yb3+. These results are justified by the host dependence of energy position of the 4f75d1 levels of Tb3+.