Optical characterization and the energy level scheme for NaYP2O7:Ln3+ (Ln=Ce, Sm, Eu, Tb, Yb)

Vacuum ultra-violet spectroscopy at low temperature was performed with undoped and Ln3+-doped NaYP2O7 (Ln=Ce, Sm, Eu, Tb and Yb). The emission observed from the NaYP2O7 host was attributed to self-trapped exciton (STE) recombination. Dopant ions were well incorporated and responsible for characteristic luminescent emission in the doped samples. From excitation curves, 4f-5d transitions were identified for Ce3+, Sm3+ and Tb3+ and charge transfer processes were noticed for Eu3+, Sm3+ and Yb3+. The experimental data obtained was used to determine the positions of the energy levels of divalent and trivalent lanthanides relative to the valence and conduction band of this compound. The experimentally derived levels are in good agreement with model predictions. The results are valuable to provide a better understanding on the performance of NaYP2O7 and related diphosphates as luminescent materials.