Optical and spectroscopic properties of Er-doped niobium germanosilicate glasses and glass ceramics

Erbium-doped glasses with the molar composition 40GeO2·10SiO2·25Nb2O5·25K2O, plus 0.1–4 mol% of ErO1.5, have been prepared by conventional melt quenching technique and their density, refractive index and characteristic temperatures have been determined. Transparent glass ceramics containing 1 and 2 mol% of ErO1.5 were also prepared and their XRD patterns and Raman spectra have been recorded and the crystalline phase K3.8Nb5Ge3O20.4 has been identified. UV/visible absorption spectra of the glasses and glass ceramics have been recorded and the resulting data was used for the Judd–Ofelt analysis, from which the Ω2, Ω4 and Ω6 parameters were determined. Photoluminescence measurements of the glasses, at 1.54 μm, showed an increase in intensity with increasing Er3+ concentration and a full width at half maximum ranging from ∼ 40 to 47 nm for 0.1% and 4% ErO1.5, respectively. Radiative lifetimes of 4.3 and 5.5 ms were obtained for the 0.4 and 2% ErO1.5 doped glasses, respectively, while the measured lifetimes varied between 4.5 and 3.2 ms for the same compositions. Quantum efficiencies of 86% and 58% were obtained for the 1% and 2% Er-doped glasses, respectively. A quenching concentration of 6.2 × 1020 ions/cm3 was obtained for the glasses, corresponding to ∼ 3.8 mol% of ErO1.5. The crystallization of the Er-doped samples led to similar intensities of the 1.54 μm emission band as well as similar full width at half maximum, however a decrease was observed both in the radiative and the measured lifetimes, although quantum efficiencies remained around 85% and 54% for the 1% and 2% Er-doped glass ceramics, respectively.