Luminescence and energy transfer phenomena in Gd3 (Al,Ga)5O12 crystals single doped with thulium and co-doped with thulium and holmium

Single crystals of Gd3Al2.5Ga2.5O12 (GAGG) doped with Tm3+ ions and co-doped with Ho3+ and Tm3+ ions were grown by the Czochralski technique and investigated employing methods of optical spectroscopy. The room temperature absorption spectra of GAGG:Tm3+ were analysed in the framework of the Judd-Ofelt theory. Obtained phenomenological parameters Ω2 = 0.62 × 10−20 cm2, Ω4 = 1.41 × 10−20 cm2 and Ω6 = 0.80 × 10−20 cm2 were used to determine rates of radiative transitions, branching ratio values and radiative lifetimes for excited multiples of incorporated Tm3+ ions. Effect of Tm3+ concentration on decay curves of Tm3+ luminescence was examined and spectroscopic parameters characterizing the donor-acceptor interaction responsible for self-quenching of the emission from the 1D2, 1G4 and 3H4 multiplets were evaluated applying the Inokuti-Hirayama model. The crystal field splitting of Tm3+ multiplets were determined based on low temperature absorption and emission spectra. The emission cross section for Tm3+: 3F4 → 3H6 luminescence was determined to be 0.31 × 10−20 cm2 at maximum and corresponding experimental lifetime amounts to 4.3 ms resulting in quantum efficiency η = 0.79. The calculated ratio of Tm-Ho to back-transfer processes (CTm-Ho/CHo-Tm) is 5.18.