Luminescence of LaBr$_3$: Ce,Hf crystals under photon excitation in the ultraviolet, vacuum ultraviolet, and X-ray ranges

This study has been carried out using synchrotron radiation, time-resolved luminescence ultraviolet and vacuum ultraviolet spectroscopy, optical absorption spectroscopy, and thermal activation spectroscopy. It has been found that, in scintillation spectrometric crystals LaBr$_3$: Ce,Hf characterized by a low hygroscopicity, along with Ce$^{3+}$ centers in regular lattice sites, there are Ce$^{3+}$ centers located in the vicinity of the defects of the crystal structure. It has also been found that the studied crystals exhibit photoluminescence (PL) of new point defects responsible for a broad band at wavelengths of 500–600 nm in the PL spectra. The minimum energy of interband transitions in LaBr$_3$ is estimated as $E_g\sim$ 6.2 eV. The effect of multiplication of electronic excitations has been observed in the range of PL excitation energies higher than 13 eV (more than 2$E_g$). Thermal activation studies have revealed channels of electronic excitation energy transfer to Ce$^{3+}$ impurity centers.