High-resolution spectroscopic studies of random strains in ferroelastic domains in the LaAlO3:Tm3+ single crystal

Comprehensive spectroscopic, magnetization, and theoretical studies of a LaAlO 3 :Tm 3+ single crystal in the ferroelastic R 3 ‾ c phase are reported. The Tm 3+ ions substitute for the La 3+ ions at sites with the D 3 symmetry. High-resolution absorption, photoluminescence, and site-selective emission and excitation spectra were measured in the broad spectral range from 4000 to 28000 cm −1 at temperatures 4.2–5 K. The two-fold degeneracy of the ground state of Tm 3+ was uncovered by magnetization measurements. Energies and symmetry properties of wave functions of crystal-field levels of the Tm 3+ ions were determined and successfully reproduced by crystal-field calculations. Specific profiles with a dip at the center of spectral lines corresponding to transitions involving non-Kramers doublets give evidence for random strains in the studied multidomain sample. The value of 0.1–0.8 cm −1 of deformational splitting of non-Kramers doublets exceeds hyperfine splittings by more than an order of magnitude. The observed line shapes were successfully modeled assuming the interaction of Tm 3+ ions with random deformations described by the generalized two-dimensional Lorentzian distribution with the width of (7 ± 0.5) ⋅ 10 −4 . The simulation was performed using the electron-deformation coupling constants calculated in the framework of the exchange-charge model. • High-resolution spectroscopy, identification of spectral lines. • Crystal field energies and symmetry properties of wave functions. • Deformational fine structure of spectral lines. • Distribution function of random strains and modeling of spectral envelopes.