Luminescence and recombination processes in bulky Li6Gd x Y1 − x (BO3)3:Eu crystals

Abstract

The luminescence and recombination processes in crystals of lithium borates Li6GdxY1 − x(BO3)3:Eu have been investigated. The steady-state X-ray luminescence (XRL) spectra, the temperature dependences of the XRL intensity, and the thermally stimulated luminescence (TSL) spectra have been measured for the Li6Gd(BO3)3, Li6Eu(BO3)3, Li6Y0.5Gd0.5(BO3)3:Eu, and Li6Gd(BO3)3:Eu compounds in the temperature range of 90–500 K. It is established that the band at 312 nm, which is due to the 6PJ → 8S7/2 transitions in Gd3+ ions and the group of lines at 580–700 nm, which are due to the 5D0 → 7FJ (J = 0 … 4) transitions in Eu3+ ions dominate in the XRL spectra. The XRL intensity in these bands increases several times with a change in temperature from 100 to 400 K for undoped crystals. The likely mechanisms of the observed temperature dependence of the XRL intensity and their relationship with the features of electronic-excitation energy transfer in these crystals are discussed. The spectra of all crystals under study exhibit a dominant composite TSL peak with a maximum at 110–160 K and a series of weaker peaks, the composition and structure of which depend on the crystal type. The nature of the shallow traps, which are responsible for the TSL at temperatures below room, and their relationship with the defects of lithium cation sublattice are discussed.