NIR luminescence and laser parameters of Ca3Sc2Ge3O12 garnet host crystals activated with Tm3+ and Ho3+

We have investigated the optical properties of Ca3Sc2Ge3O12 doped with Tm3+ and Ho3+, a new potential laser material for the 2 mum region. We present a room temperature characterization of both singly and co-doped crystals, including the absorption spectra in the visible and NIR regions, the NIR fluorescence spectra and the decay time measurements. In particular, attention has been focused on the H-3(4) <-- H-3(6) (Tm3+) absorption transition lying in the 800 nm region and suitable for diode laser pumping and on the Tm3+-Ho3+ energy transfer process in order to improve the efficiency of the Ho3+ emission. From the experimental data we have calculated some parameters that deeply affect the performance of a possible NIR laser, i.e. the emission cross sections in the 2 mum region and the value of the transfer coefficient between the Tm3+ and Ho3+ ions inside this crystal.