Recombination processes and luminescence in Li₆Gd_xY_1−x(BO₃)₃-Eu crystals

Abstract

The results of investigation of thermally stimulated recombination processes and luminescence in Li 6 Gd x Y 1-x (BO 3 ) 3 -Eu crystals are presented. The steady-state luminescence spectra under X-ray excitation (XRL), the temperature dependence of steady-state luminescence intensity and the thermally stimulated luminescence curves (TSL) were measured at 90-500 K. In the steady-state X-ray luminescence spectra the band at 312 nm related to 6 P J → 8 S 7/2 transitions in gadolinium ion and bands group at 580-700 nm associated with 5 D 0 → 7 F J transitions (J = 0…4) in Eu 3+ ion were found to be dominant. The intensity of steady-state XRL of these bands in undoped crystal is increased by 15 times as the temperature changes from 100 to 400 K. The probable mechanisms of temperature dependence of steadystate luminescence intensity and their association with energy transfer of electronic excitations in these crystals are discussed. The investigations have shown the principle complex TSL peak with maximum at 150 K and a number of weaker peaks. The thermal activation parameters (activation energy, pre-exponential factor, kinetic order) for all intense TSL peak have been determined. The origin of small trapping centres caused TSL below room temperature and their association with defects in lithium cation sublattice is discussed.

Luminescence of impurity-bound excitons in Li6GdB3O9:Ce3+single crystals

“…It should be noted that in this paper we will focus on the spectroscopic data concerning only the luminescence properties of the impurity-bound excitons in LGBO:Ce. The other spectroscopic data concerning the usual 5d-4f emission of Ce 3+ and 4f-4f emission of Gd 3+ in LGBO crystals as well as the reflection spectra of LGBO crystals have been reported in separate papers [13][14][15][16][17][18][19][20].…”

“…However, the radiative decay of impurity-bound excitons in LGBO crystals, doped with Ce 3+ ions, has not yet been observed upon ultraviolet (UV) or vacuum UV excitations. One reason for this stems from the fact that the characteristic absorption bands of the crystal due to optical transitions of 8 S 7/2 → 6 I j and 8 S 7/2 → 6 G j in the Gd 3+ host ions coincide with the expected positions of the energy bands of the luminescence and excitation of impurity-bound excitons [13][14][15][16][17][18].…”