Thermally stimulated relaxation in insulating CdF2:Eu3+

The mechanism is investigated by which photogenerated Eu2+ ions in CdF2:Eu3+ relax back to the Eu3+ charge state upon thermal relaxation. Thermally stimulated luminescence (TSL) and conductivity (TSC) techniques are combined with photoluminescence and EPR measurements as a function of temperature at various Eu3+ concentrations. Experimental evidence is presented for this relaxation to occur via thermal release of electrons, trapped in the Eu2+ donor state, into the conduction band and subsequent radiationless recombination with F0 interstitials. Analysis of the thermoluminescence emission spectra suggests TSL to be due to energy transfer from the so produced F--interstitials to neighbour Eu3+ ions which are located in a tetragonal crystal environment.