Optical absorption of Er3+ in RbTiOPO4 and KTiOPO4

The optical absorption of Er3+ in RbTiOPO4 (RTP) and KTiOPO4 (KTP) single crystals has been characterized at 5 K and 300 K temperatures. The room temperature oscillator strengths of Er3+ obtained in both lattices are similar although in KTP the uncertainty is higher due to the lower concentration of Er in the samples available. The results obtained in RTP have been analysed by using the Judd-Ofelt theory. The effective Judd-Ofelt parameters obtained for Er3+ in RTP are Ω2eff = 12.85x10-20 cm2, Ω4eff = 0.60x10-20 cm2, Ω6eff = 0.57x10-20 cm2. The photoluminescence transition radiative rates, branching ratios and radiative lifetimes of Er3+ in these crystals have been calculated for all de-excitations from the 4G9/2 multiplet. The 4I13/2 → 4I15/2 erbium emission has been characterized. The low temperature optical absorption and photoluminescence suggest the coexistence of two erbium centres in both lattices, which we have tentatively ascribed to the occupancy with different population densities of the two titanium lattice sites. (author)