Excitation-density-dependent competition between radiative and nonradiative annihilations of core holes produced by ion irradiation of a single-crystallineBaF2

It was found that the decay time of the Auger-electron-free luminescence of ${\mathrm{BaF}}_2$ decreases with increasing linear energy transfer (LET) or excitation density. The luminescence decayed exponentially at the initial and final stages, in contrast with a single exponential for photoirradiation. The decay time of a fast component was reduced with increasing LET, while that of a slow component was invariant. A model that Auger-free transitions compete with nonradiative recombinations between core holes and quasifree electrons can explain these experimental results. The recombination rate attained a constant value near the LET of 1.5 MeV/amu Kr ion. The reciprocal of the recombination rate at this LET gives the lifetime of the core exciton.