Abstract
Mechanisms of photoluminescence in antizeolite fluoride borates (AFBs) doped by copper ions are interpreted based on a comparison between experimental and computational approaches. Doped AFBs demonstrate the effect of thermally stimulated photoluminescence and hold a promise for the use as radiation detectors. AFBs are built of porous framework [Ba 12 (BO 3 ) 6 ] 6+ with channels along the c axis. Lattice channels can accommodate various guest anionic groups. In this study, we present the results of modeling the electronic and optical properties of Cu-containing fluoride borates with [Cu(OH) 4 ] 3– (monovalent Cu) and [Cu(OH) 6 ] 4– (divalent Cu) as anionic groups. It is found that monovalent Cu + ions create occupied Cu-3d states near the top of the valence band, whereas divalent Cu 2+ ions create vacant Cu-3d states near the bottom of the conduction band. These states can serve as traps for electronic excitations and affect both the linear absorption and photoluminescent (PL) properties. PL spectra calculations were performed using two ab initio methodologies: (i) molecular dynamics (MD) sampling and (ii) time integration along with the progression of subsequently occupied excited states. The results show that the theoretical PL spectra calculated at a temperature of 10 K are instrumental in interpretation of experimental data obtained at 77 K. This effect is due to the strong dependence of Cu–OH distances in anionic groups along MD trajectories at given temperatures, which, in addition, manifests itself in the temperature dependence of the times and relaxation paths of electronic excitations. The results obtained open the way to designing new materials with predetermined properties for applications in radiation detectors based on thermally stimulated photoluminescence.