Optical and EPR study of the Ce3+ luminescent centers in the Lu2SiO5:Ce single crystalline films

The work presents the results of optical and EPR investigations of Ce3+ incorporation into Lu2SiO5 single crystalline films (LSO:Ce SCFs), grown using the liquid phase epitaxy method. It also examines the conversion of Ce valence state as a result of the LSO:Ce SCF thermal treatment in reducing and oxygen-rich atmospheres. The EPR study revealed the presence of only one type of Ce3+ center (Ce1), corresponding to the localization of Ce3+ ions in sevenfold coordinated positions within the Lu2SiO5 host. No spectra of Ce2 centers (sixfold coordinated Ce3+ positions) were detected in the LSO:Ce SCF films, indicating their negligibly small concentration. High-temperature annealing of the as grown films in air reduces the concentration of Ce3+ ions to a level undetectable by EPR, due to the Ce3+ Ce4+ conversion. In contrast, thermal treatment in a 95%N2 + 5%H2 reducing atmosphere results in the opposite Ce4+ Ce3+ conversion, substantially increasing the concentration of Ce3+. The oxidation/reduction treatment and Ce³⁺/Ce⁴⁺ valence state changing lead to notable variations in the scintillation light yield and decay kinetics of the LSO:Ce SCFs, offering a method to tune their scintillation figure of merit.