Energy transfer from CsI host lattice to Ag− centers in CsI:Ag− crystals

Abstract Luminescence properties of CsI single crystals doped with Ag − ions have been investigated under excitation in the energy range from 3 to 12 eV. When the crystals are excited at photon energy around 3.79 eV corresponding to the C absorption band of Ag − centers, the A′ and C′ luminescence bands of the Ag − center are observed at 2.53 and 3.45 eV, respectively. Under excitation above the band gap energy of CsI (6.1 eV), the luminescence bands originating from the on- and off-center type self-trapped excitons (STEs) of CsI are observed at 3.60 and 4.30 eV, respectively, in addition to the A′ and C′ luminescence bands. The excitation spectra for the A′ and C′ luminescence in the energy region above the band gap energy are nearly the same as that for the off-center STE luminescence. The temperature dependence of the A′ luminescence intensity is similar to that of the off-center STE luminescence intensity in the luminescence spectra under the excitation above the band gap energy. Furthermore, the temporal behavior of the C′ luminescence band resembles that of the off-center STE luminescence band. On the basis of the characteristics of the A′, C′ and off-center STE luminescence bands, the energy transfer mechanism from the CsI host crystals to the Ag − impurity centers in the CsI:Ag − crystals is discussed.