Defect luminescence in CaF2 nanoparticles

The stationary X-ray excited luminescence (XEL) spectra at 80 and 294 K as well as the thermally stimulated luminescence (TSL) in the 80-320 K range of the CaF2 nanoparticles with various grain sizes (20-60 nm) were studied. Similarly to the earlier studied single CaF2 crystals, specific bands were revealed both for XEL and for TSL of the radiation defects. XEL spectra of the CaF2 nanoparticles contain emission bands in the 240-500 nm region caused by excitonic-like excitations localized at the radiation defects of the CaF2 lattice as well as recombination luminescence band at 560 nm. TSL integral curves of CaF2 nanoparticles contain peaks that correspond to the delocalization of the hole centers and to their recombination with F-centers and with electronic centers of the cationic sublattice. Activation energies of delocalization processes of the hole centers were determined. It was established that the light output of both XEL and TSL of the CaF2 nanoparticles increases with an increase of size of nanoparticles in the region of 20-50 nm. (C) 2015 Elsevier B.V. All rights reserved.