Luminescence study of ScF3 single crystals excited by electron beam or UV-VUV synchrotron radiation

ScF3 has a simple cubic ReO3 type structure down to at least 10 K and exhibits a rare property of isotropic negative thermal expansion (NTE) over a large temperaturerange.In order to reveal the manifestations of the NTE effect in optical spectra, we have performed the following investigations:(a) cathodoluminescence spectra measurements of ScF3 single crystals in temperature range 10-300 K;(b) VUV-luminescence excitation using synchrotron radiation at MAX-Laboratory in Lund;(b) Thermally stimulated luminescence (TSL) study between 80 and 350 K, excited by an electron beam (10 keV) or VUV radiation.From the TSL data analysis and the comparison with other metal fluorites, we can conclude that in ScF3 there is the effective self-trapping of holes in the form of Vk cen-tres and their thermal destruction occurs at about 100 K. From the creation (excitation) spectra of several TSL peaks as well as the VUV-luminescence excitation spectra, we can conclude that the value of band gap energy in ScF3 exceeds 11 eV. This is in good agreement with the Eg data for other fluorites, such as MgF2, CaF2 and LiF.