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

Abstract

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– x AxAlO4H ( 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-4 f and 5 d 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.

Pressure-Triggered Fluorescence Intensity Ratio Variations of YNbO4:Bi3+/Ln3+ (Ln = Eu or Sm) for High-Sensitivity Optical Pressure Sensing

“…For the LnNbO 4 series of structures, it was also shown that [LnO 8 ] is significantly more compressible than [NbO 6 ], and that this inhomogeneous compressibility within the lattice can lead directly to irregular changes in bond lengths . Of course, the similar phenomenon that bond lengths of phosphors increase under high pressure has been reported . The Raman vibration peaks at decompression back to 0 GPa were the same as the initial ones, which indicated that the crystal structure has a good stability of pressure recovery and facilitates applications in pressure sensing.…”

“…16 Of course, the similar phenomenon that bond lengths of phosphors increase under high pressure has been reported. 17 The Raman vibration peaks at decompression back to 0 GPa were the same as the initial ones, which indicated that the crystal structure has a good stability of pressure recovery and facilitates applications in pressure sensing.…”

A brief review of characteristic luminescence properties of Eu3+ in mixed-anion compounds

“…To obtain a highly sensitive pressure sensor, materials that are easily compressible and have large local structural changes under high-pressure conditions are promising. For example, the pressure-sensing properties of Eu 2+ -doped phosphors are 1.4 nm GPa −1 for Ca 3 Y 2 (SiO 4 ) 3 :Eu 2+ , 247 2.2 nm GPa −1 for CaF 2 :Eu 2+ , 238 ∼2.6 nm GPa −1 for Sr 2 BaAlO 4 H, 253 and 19 nm GPa −1 for BaCN 2 :Eu 2+ . 239 The spectral shift is larger in host compounds with high compressibility due to H − ions or molecular anions such as NCN 2− than in compounds with rigid structures.…”