High-resolution spectroscopy of YAl$_3$(BO$_3$)$_4$–Pr$^{3+}$ crystal

Optical absorption spectra of YAl$_3$(BO$_3$)$_4$–Pr$^{3+}$ crystals in the temperature range of 5–300 K in polarized light were studied by high-resolution Fourier spectroscopy (up to 0.1 cm$^{-1}$). The energies of crystal-field sublevels of 12 multiplets of the Pr$^{3+}$ ion were determined. The observed splitting of a number of spectral lines corresponding to singlet-doublet transitions is due to the influence of random lattice deformations. The complex structure of the singlet-singlet transition line to the $^3P_0$ level is explained by the presence of additional centers "Pr$^{3+}$ ion near a lattice defect". Presumably, such defects are uncontrolled impurities entering the crystal during its growth by solution-melt technique.