Thermal stability and spectroscopic properties of Er3+-doped lead fluorogermanate glasses

The thermal characterization and spectroscopic properties of Er3+-doped image glasses were investigated experimentally. With the replacement of PbO by PbF2 the thermal stability of glasses is improved and the infrared fluorescence intensity at 1530 nm is increased. The Judd–Ofelt intensity parameters, radiative transition rates, and fluorescence lifetimes of the excited 4I13/2 level of Er3+ ions were calculated from Judd–Ofelt theory. The asymmetric ligand field around Er3+ ions resulted from the incorporation of PbF2 into germanate glasses, broadens the infrared emission spectra at 1530 nm. Upconversion luminescence in the investigated glasses was observed at room temperature under the excitation of 976 nm laser diode. The glass image exhibits the maximum upconversion emission intensity, while no frequency upconversion luminescence was observed in the image glass. The quadratic dependence of the green and red emissions on excitation power indicates that two-photon absorption contributes to the visible emission under the 976-nm excitation.