Spectroscopic properties of Er3+-doped oxyfluoro-germanate glass ceramics: A Judd-Ofelt theory analysis

The upconversion (UC) luminescence of Er3+-doped oxyfluoro-germanate glasses and glass ceramics is studied in terms of the Judd-Ofelt (J-O) theory. Using the least square method, three J-O intensity parameters (i.e., Ω2, Ω4, and Ω6) are determined from the experimental absorption spectra via the line strength equation of electric-dipole (ED) transition Sed of J→J′ transitions. The calculation results are calibrated by the detected fluorescence lifetime of Er3+: 4I13/2 level to obtain the truth value of the J-O parameters in the presence of transmission light scattering. Combining the obtained J-O parameters, we analyze the structure characteristics in the vicinity of the doped Er3+ ions, the bonding properties between rare earth ions (REs) and ligand anions, the crystallization mechanism of fluoride, as well as the microstructure of the glass ceramics. Furthermore, the effect of crystallization on the spectroscopic properties of Er3+-doped oxyfluoro-germanate glasses is also explored.