Decay enhancement of self-trapped excitons at high density and low temperature in an ion-irradiated BaF2 single crystal

The decay of the luminescence due to self-trapped excitons (STE) induced by ion irradiation of a BaF2 single crystal has been measured. It is shown that the decay of STE created by ion irradiation is much faster than those created by photon and electron irradiation; such decay enhancement is further increased with increasing projectile-ion mass and with decreasing temperature. These results are explained in terms of the effect of high-density excitation by ion irradiation. A competition kinetics between the spontaneous decay and the decay through a nonradiative exchange interaction can simulate the decay curves well. Both effects of excitation density and of temperature attain an ultimate decay time of 150 ps. This may suggest that interaction between the precursors of STE's, such as free excitons, plays a main role in incipient tracks.