Electron–Phonon Coupling in Luminescent Europium-Doped Hydride Perovskites Studied by Luminescence Spectroscopy, Inelastic Neutron Scattering, and First-Principles Calculations

Abstract

We present a case study on the vibrational coupling of lattice phonons to the electronic 4f 7 ( 8 S 7/2 ) -4f 6 5d 1 (e g ) transition of divalent europium in the hydrides and deuterides LiMH 3 and LiMD 3 (M = Sr, Ba). For low doping concentrations, these compounds show extraordinarily well-resolved vibronic fine structures at low temperatures.Besides luminescence emission spectroscopy of the europium-doped compounds, we carried out inelastic neutron scattering experiments of the europium-free compounds.The phonons coupling to the electronic transition are identified and a good agreement between the vibronic and the inelastic neutron scattering data is found. The low energy acoustic modes do not significantly change upon replacing hydride by deuteride, whereas a decrease by a factor of approximately √ 2 can be observed for the higher energy optic modes. Furthermore, we compare these experimental results to density functional calculations performed with the Vienna Ab Initio Simulation Package.Knowledge of the phonons of a host material is of great importance, because phonons have a large influence on the optical properties, such as linewidths or luminescence quenching. Hydride-containing host lattices are an ideal model system, since 1 H can easily be replaced by 2 D, so that isotope effects can be investigated.

Recent Advances in Rare Earth‐Doped Hydrides

“…120 K the spectra started to show a well‐resolved vibronic fine structure. The vibrational features were assigned to different modes and their overtones and, for comparison, inelastic neutron scattering of the Eu 2+ ‐free compounds was carried out, the spectra were compared to simulated spectra from density functional calculations and a good agreement was observed . A comparison of the vibrational modes in the excitation and emission spectra yielded the information that the binding strength of the Eu–H‐bond becomes weaker in the Eu 2+ 5d (e g ) excited state.…”

Importance of Long‐Range Channel Sr Displacements for the Narrow Emission in Sr[Li2Al2O2N2]:Eu2+Phosphor

“…We note however that some previous vibronic studies, mixing experimental and theoretical analysis, were already carried out. [ 18–21 ]…”

Nephelauxetic effect of the hydride ligand in Sr2LiSiO4H as a host material for rare-earth-activated phosphors

“…For the past decades, hydrides and mixed anion hydrides containing Eu 2+ dopant have been reported to exhibit green-red luminescence. 10,[14][15][16][17][18][19][20] However, their poor stability in air and moisture limits their application. In contrast, we have recently demonstrated that oxyhydride GdHO is stable in ambient air and can act as a phosphor host for Tb 3+ .…”