The charge states’ conversion of the activator ions in CaF2:Eu nanophosphors

Abstract

ABSTRACTAccording to stationary X-ray-excited luminescence spectra and thermally stimulated luminescence spectra of CaF2:Eu nanophosphors, it was found that Eu3+ → Eu2+ conversion can occur during thermal annealing of fine-grained (d = 25 nm) nanoparticles in the 200–800°C range, which is accompanied by an increase in their size within 40–189 nm. An important role of the exciton mechanism of Eu2+ luminescence excitation was revealed according to the temperature dependence of X-ray-excited luminescence spectra of CaF2:Eu nanoparticles of 114 nm size. The maximum of the X-ray-excited luminescence light output of CaF2:Eu nanophosphors in the Eu2+ ions’ emission band was traced out at 400–500°C annealing temperature and at the size of nanoparticles of 114–180 nm. The subsequent growth of the annealing temperatures, particularly in the 800–1000°C range, causes the reduction of X-ray-excited luminescence light output because of the increment of lattice defects’ concentration due to a sharp increase in the size of nanoparticles and their agglomeration.