Pressure-dependent photoluminescence of Eu-activated aluminate hydride Sr3−x AxAlO4H:Eu2+ (A = Ca, Ba; x = 0, 1): Application of advanced U-determination technique for luminescence wavelength prediction

The increasing attention on the unique properties of oxyhydride materials motivates the exploration of their potential applications in optical fields, and the theoretical studies of their luminescence properties are still under progress. Here, we report the experimental and theoretical high-pressure photoluminescence (PL) studies on Eu-activated Sr3–xAxAlO4H (A = Ca and Ba; x = 0 and 1) oxyhydride materials. Under hydrostatic pressures from ambient pressure up to 6.41 GPa, the luminescence band in all the samples exhibits redshift with increasing pressure and the highest energy-shift rate of −101.85 cm−1/GPa was observed in Sr3AlO4H:Eu2+. The asymmetric bands were deconvoluted into two peaks corresponding to the two Eu sites with different coordination environments. Although the shift rates of Eu2+ centers in Sr3AlO4H are not remarkable as expected for the large compressibility of hydride ion ligands, their pressure-dependences in opposite directions were successfully reproduced by constrained density functional theory calculations using the advanced on-site Coulomb interaction parameter (U) determination method. The lower shift rate as seen in conventional oxide phosphors indicates that Eu-4f and 5d level positions are determined by the interaction with less compressive oxide ion ligands. Therefore, the high shift rate required for pressure sensing applications is expected in more hydrogen-rich oxyhydrides and related hydride compounds.