Local structure around Er 3+ in GeO2-TeO2-Nb2O5-K2O glasses and glass-ceramics

Erbium-doped germanotellurite glasses and glass-ceramics in the (80-x) GeO2-xTeO2-10Nb2O5-10K2Osystem (x=0-80 mol%) have been prepared. The heat treatments were performed based on differential scanning calorimetry data. Several crystalline phases, including?-TeO2,?-TeO2andGeO2(?-quartz), togetherwithK [Nb1/2TeO2/3]2O4.8, could be distinguished in the X-ray diffraction patterns. The 1.5 ?m photoluminescence (PL) emissionof Er 3+ ( 4 I13/2->4 I15/2) 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 4 I13/2->4 I15/2transition, indicating that the environment around the Er 3+ 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 Er 3+ coordination shell before and after heat treatments. The glass compositions presented only one coordi-nation shell around Er 3+ , composedof oxygen, while two coordination shells could be distinguished for the heat treated samples: afirst 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 to50), and of Ge and Er ions, for theGe-rich compositions (x=10 and 20)