Effect of quenching processes on the decay of fast luminescence from barium fluoride excited by VUV synchrotron radiation

Abstract

The problem of quenching the luminescence associated with interatomic radiative transitions from the valence band to the deeper lying core level is studied for ${\mathrm{BaF}}_{2}$, which is known to be the fastest inorganic scintillator. The measurements of excitation spectra and time decay kinetics of the fast fluorescence component (220 nm) for ${\mathrm{BaF}}_{2}$ crystal excited by photons in the VUV spectral region from 16 to 100 eV are discussed. The quenching process is exhibited in the shortening of this decay and in the decrease of the quantum efficiency. The kinetics is nonexponential for all energies. These effects depend on the excitation photon energy and the angle of light incidence. This behavior is explained by the surface quenching (as has been supposed earlier) and the energy transfer to the excitations produced by the same photon. The relative effect of these processes depends on the excitation energy. For energies below 30 eV the surface quenching dominates, whereas for higher energies the main quenching process is caused by the energy transfer from the core hole to other electronic excitations. The same effect can be observed in other ionic crystals in which the Auger decay of core hole is energetically forbidden.