Optical transition properties of rare-earth ions in nonfluoride halide glasses

Abstract

Optical transition properties of Er<SUP>3+</SUP> ions in ZnCl<SUB>2</SUB>-KCl-BaCl<SUB>2</SUB> glass were studied and were discussed on the comparison with those in the other glass systems, i.e., ZrF<SUB>4</SUB>-based and Ga<SUB>2</SUB>S<SUB>3</SUB>-based glasses. Judd-Ofelt analysis was performed using eight absorption bands of Er<SUP>3+</SUP> in the ZnCl<SUB>2</SUB>-based glass. Among the Judd- Ofelt intensity parameters, the (Omega) <SUB>2</SUB> was larger than that of the ZrF<SUB>4</SUB>-based glass. This is probably due to the covalency of the bonds of the rare-earth and ligand ions in comparison with those of the ZrF<SUB>4</SUB>-based glass. Decay curves of the emission from the <SUP>4</SUP>F<SUB>5/2</SUB>, <SUP>4</SUP>F<SUB>7/2</SUB>, <SUP>4</SUP>S<SUB>3/2</SUB>, and <SUP>4</SUP>F<SUB>9/2</SUB> levels were measured. From the lifetime data and the radiative transition probabilities calculated using the Judd-Ofelt intensity parameters, multiphonon relaxation rates are estimated for the four excited levels. The multiphonon relaxation rates of the <SUP>4</SUP>F<SUB>5/2</SUB>, <SUP>4</SUP>F<SUB>7/2</SUB>, and <SUP>4</SUP>F<SUB>9/2</SUB> were much smaller than those in the ZrF<SUB>4</SUB>- based and Ga<SUB>2</SUB>S<SUB>3</SUB>-based glasses. This is the consequence of the extremely low-phonon-energy property of the ZnCl<SUB>2</SUB>-based glass. The multiphonon relaxation rates were inversely proportional to the exponential of the energy gap between the emission and the next-lower levels (a so- called `energy-gap low') as well as the other glass systems.