Up-conversions in Ho3+ doped tellurite glass

Optical absorption and photoluminescence properties of Ho3+ doped lithium tellurite glasses have been investigated. The observed spectra have been analysed on the basis of Judd-Ofelt theory. Judd-Ofelt intensity parameters for Ho3+ have been used to calculate the transition probability, branching ratio, radiative lifetime, etc. Stimulated emission cross-section has been determined for 5F4(5S2) → 5I8 transition. Up-conversion emissions have been observed at 487 (blue), 545 (green) and 687 nm (red) at room temperature in Ho3+ on excitation with 812 nm radiation from a Ti-sapphire laser. Variation of the emitted intensity at these wavelengths as a function of the excitation power indicates the operation of a two-step process. The temperature dependence (between 298 and 533 K) of the fluorescence as well as the up-conversion emission has been studied. Pumping with 532 nm line of Nd:YAG laser gives a similar but weaker up-conversion. Concentration quenching is seen for Ho3+ concentration beyond 2 mol%.