Energy transfer processes involving different luminescence centres in BaF2:Ce

The luminescence of cerium-doped barium fluoride crystals has been investigated as a function of wavelength and time. For excitation UV light, x-rays and gamma rays were used. The well known cross luminescence (CL) near 200 nm and self-trapped exciton luminescence (STE) near 300 nm, which are due to excitations of the host lattice, are observed at low cerium concentrations. For increasing cerium concentrations, the CL and STE emission is gradually replaced with cerium emission. Luminescence due to at least three different cerium related centres was found. The decay of the luminescence under gamma excitation is non-exponential. At low cerium concentrations, its duration is much longer than the decay time of the excited level of the predominant cerium centre. At higher cerium concentrations, the luminescence decays faster. These observations are explained in terms of an energy transfer model. (author)