Influence of high pressure on Ce³⁺ luminescence in LuAlO₃ and YAlO₃ single crystals and single crystalline layers

Results of spectroscopic studies at ambient and high pressures of a LuAlO₃:Ce³⁺ (LuAP:Ce) single crystalline film (SCF) as well as LuAP:Ce and YAlO₃:Ce (YAP:Ce) single crystals are reported. Room temperature absorption measurements of the single crystals in the vacuum UV region allowed establishing the bandgap energies of 7.63 eV for YAP and 7.86 eV for LuAP, with an assumption of the direct band-gaps. Luminescence of Ce³⁺ in LuAP and YAP bulk crystals was measured as a function of temperature from 6 K up to 873 K. Temperature quenching of the Ce³⁺ luminescence in YAP:Ce was observed above 650 K, which is related to the location of the lowest Ce³⁺ 5d level at 1.27 eV below the conduction band minimum. No temperature quenching occurred in LuAP:Ce up to 873 K, mostly due to the lower energy of the 4f levels with respect to the valence band maximum. The barycenter energies and splittings of Ce³⁺ 5d states in YAP and LuAP at room temperature were precisely established. Theoretical calculations of the Ce³⁺ 5d states energy structure under pressure revealed a discrepancy between the obtained experimental results and the prediction of Dorenbos' theoretical model. The discrepancy can be removed if instead of the 5d state of the free Ce³⁺ ion the bandgap of the compound is taken as reference energy for the red-shift of the 5d level. This hypothesis also allows us to take into account the pressure-induced increase of the bandgap energy, expected for the studied compounds. Pressure dependences of LuAP:Ce luminescence spectra suggest that a certain type of phase transition occurs above 15 GPa.