Local structure around Er3+ in GeO2-TeO2-Nb2O5-K2O glasses and glass-ceramics

Erbium-doped germanotellurite glasses and glass-ceramics in the (80-x) GeO2-xTeO(2)-10Nb(2)O(5)-10K(2)O system (x = 0-80 mol%) have been prepared. The heat treatments were performed based on differential scanning calorimetry data. Several crystalline phases, including alpha-TeO2, delta-TeO2 and GeO2 (alpha-quartz), together with K [Nb1/2TeO2/3](2)O-4.8, could be distinguished in the X-ray diffraction patterns. The 1.5 mu m photoluminescence (PL) emission of Er3+ (I-4(13/2) -> I-4(15/2)) has been studied in the glasses and glass-ceramics and the latter revealed a general increase in the bandwidth of the emission spectra, compared to the PL peak of the starting glass samples. Some heat treated compositions presented Stark splitting of the I-4(13/2) -> I-4(15/2) transition, indicating that the environment around the Er3+ ions had changed from an amorphous matrix to a more ordered environment. Extended X-ray Absorption Fine Structure spectroscopy measurements were performed in order to investigate the Er3+ coordination shell before and after heat treatments. The glass compositions presented only one coordination shell around Er3+, composed of oxygen, while two coordination shells could be distinguished for the heat treated samples: a first oxygen coordination shell for all heat treated compositions and a mixed second nearest neighbor shell of Te and Er ions, for the Te-rich compositions (x = 80 to 50), and of Ge and Er ions, for the Ge-rich compositions (x = 10 and 20). (c) 2012 Elsevier B.V. All rights reserved.