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–xTeO2–10Nb2O5–10K2O system (x = 0–80 mol%) have been prepared. The heat treatments were performed based on differential scanning calorimetry data. Several crystalline phases, including α-TeO2, δ-TeO2 and GeO2 (α-quartz), together with K[Nb1/2TeO2/3]2O4.8, could be distinguished in the X-ray diffraction patterns. The 1.5 μm photoluminescence (PL) emission of Er3 + (4I13/2 → 4I15/2) 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 4I13/2 → 4I15/2 transition, indicating that the environment around the Er3 + ions had changed from an amorphous matrix to a more ordered environment. ed 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).