Thulium-doped Ca4GdO(BO3)3 crystals.: An investigation of radiative and non-radiative processes

An extensive investigation of optical properties was carried out for Tm3+-doped Ca4GdO(BO3)(3) crystals in the 5-300 K temperature range. Based on absorption and emission spectra at 5 K, crystal field levels of active ions have been located. Non-equivalent sites for Tm3+ in the Ca4GdO(BO3)(3) matrix have been demonstrated. Lifetimes and the fluorescence dynamics were studied as a function of temperature and concentration of thulium ions. The Judd-Ofelt analysis of absorption spectra and the Inokuti-Hirayama model for energy transfer between activator ions provided information on radiative processes and non-radiative relaxation of excited states. Additionally, multiphonon emission was taken into account to explain a very strong quenching of the H-3(4) and the F-3(4) fluorescence.