PNNL

Abstract

Tellurite glass systems have important commercial applications in optical communication due to its high refractive index, good infrared transmittance, and high optical nonlinearity. Previously, we studied optical absorption. A local Nd-O structural transition, in the vicinity of 1 mol% Nd2O3, was found; the asymmetry of Nd-O ligand field was at maximum whereas, the degree of Nd-O bond covalency was in a minimum according to the Judd-Ofelt theory derived intensity parameters of the oscillator strength. In this study, we report our investigation on the structural change in the host matrix, 10Na2O-90TeO2, as a function of Nd2O3 concentration using Raman spectroscopy technique. Over the Nd2O3 concentration region from 0.5 to 2.5 mol%, our Raman spectroscopic study showed that the addition of Nd into tellurite glass converts TeO4 trigonal bipyramid (tbp) units to TeO3 trigonal pyramid (tp) units, and possibly some terminal TeO3+1 polyhedra. The Nd effect on the speciation of tellurite structural groups is similar to that of other metal cations of monovalent, divalent, and trivalent. The previously observed Nd-O local structural transition was also found in the current study. A transition, near 1 mol% Nd2O3, was observed in the correlations, both band position and intensity, between two Raman stretching vibration bands near 600 and 730 cm-1. The low frequency band represents the stretching vibration mode of TeO4 tbp units and the high frequency band represnts the stretching vibration mode of TeO3 trigonal pyramid (tp) units. Therefore, the observed transition may suggest the formation of TeO3+1 polyhedron units in the glasses with Nd2O3 concentration greater than 1 mol%. Near 465 cm-1, the bending vibration band for Te-O-Te linkages showed a significant decrease for the glass with 2.5 mol% Nd2O3, suggesting a considerable breakage of the tellurite network.