Spatial distribution of rare-earth ions andGaS4tetrahedra in chalcogenide glasses studied via laser spectroscopy andab initiomolecular dynamics simulation

Abstract

The spatial distribution of ${\text{Nd}}^{3+}$ ions and ${\text{GaS}}_{4}$ tetrahedral units in Nd-doped Ge-As-Ga-S glasses has been studied by laser spectroscopy and ab initio molecular dynamics (MD) simulations. A sharp increase in ${\text{Nd}}^{3+}$ fluorescence intensities and lifetimes was observed with increasing Ga content, and attributed to the formation of tightly bound ${\text{Nd}}^{3+}$ clusters in Ga-free glasses and the subsequent dissolution of such clusters upon Ga doping. A large modification in ${\text{Nd}}^{3+}$ sites was also identified from low-temperature site-selective excitation spectra, suggesting preferential spatial correlations between ${\text{Nd}}^{3+}$ and ${\text{GaS}}_{4}$ tetrahedra even at low Ga-doping levels. MD simulations of these materials in the liquid state showed a tendency for Ga cluster formation as well as spatial correlations between Nd and Ga atoms consistent with the experimental results. On the basis of this result, a comprehensive structural model for Nd- and Ga-doped sulfide glasses is proposed.