Spectroscopic properties of Ho3+ and Al3+ co-doped silica glass for 2-μm laser materials

Two series of Ho3+ and Al3+ co-doped silica glasses containing different Al2O3/Ho2O3 mole ratios and concentrations of Ho3+ ions were successfully prepared by the sol-gel method combined with high temperature sintering. Using the fluorescence spectra and fluorescence lifetimes, it was found that the optimum Al2O3/Ho2O3 mole ratio of Ho3+ and Al3+ co-doped silica glass for realizing a 2-μm laser is 15. Ho3+ and Al3+ co-doped silica glasses with compositions of xHo2O3-15xAl2O3-(100−16x) SiO2 (in mol%, x=0.14, 0.2, 0.3, 0.4, and 0.5) were designed to investigate the concentration dependence of the 2.0-μm emission and concentration quenching of the 5I7 emission. The Judd-Ofelt intensity parameters and the stimulated emission and absorption cross-sections of 0.3Ho2O3-4.5Al2O3-95.2SiO2 were systematically studied. The analysis on the relationship between the 5I7 lifetime and the Ho3+doping concentration reveals that self-quenching for a rather large Ho3+ doping range is well described by a limited diffusion process, and that the critical concentration for self-quenching is 4.84×1020 ions/cm3. The results show that Ho3+ and Al3+co-doped silica glass is an ideal candidate for realizing ~2-μm laser.