A luminescence spectroscopy study of new Li2BaAl2F10 single crystal

Large Li$_2$BaAl$_2$F$₁₀$ single crystals of optical quality were grown using the vertical Bridgman method. X-ray diffraction method was used to determine the crystal structure (orthorhombic symmetry Cmc2$_1$), lattice parameters, atomic coordinates. The luminescent properties were investigated using selective photoexcitation by synchrotron radiation (E = 3.7–21 eV, T = 8 K, time integrated and time-resolved spectra) as well as upon excitation with unfiltered X-ray beam (synchrotron radiation or X-ray tube). We revealed both the broadband luminescence at E$_m$ = 4.0 eV (E$_ex$=11.72 eV) attributed to the radiative annihilation of self-trapped excitons (STE) and the excitonic-type near-defect luminescence at E$_m$ = 3.0–3.2 eV (E$_ex$=11.25 eV) attributed to radiative relaxation of electronic excitations in nonequivalent structural units of the crystal lattice. The fast exponential component with lifetime of 5.6 ns, a low-intensity intermediate component with a lifetime of 75–100 ns, a constant level — pedestal (sum of the micro- and millisecond decay components) were revealed in luminescence decay kinetics. The electronic structure parameters (bandgap = 13.0 eV, low-energy onset of the intrinsic host absorption E$_c$ = 11.2 eV), the energy threshold for the excitation of STE-luminescence ( E$_th$ = 11.2 eV) are determined from spectroscopic data. Thermoluminescence (TL) has been studied (90–350 K) using spectral-integral regime. Four partially overlapping TL glow peaks were revealed, their deconvolution was done and thermal activation parameters were determined using TGCD method.