Triboluminescence of fluorites

Abstract

The room-temperature triboluminescent spectra of single crystals of CaF₂:1% Tb, CaF₂:1% Dy, CaF₂:1% Sm and CaF₂:1% Eu have been recorded using a high-gain image intensifier spectrograph. The spectra, obtained as the crystals were cut with a diamond-impregnated circular saw, show significantly more structure than that recorded in the room-temperature photoluminescent spectra. In fact the triboluminescent spectra show structure comparable with that seen in liquid-nitrogen-temperature photoluminescent spectra. Although the details of the excitation mechanism remain obscure, the triboluminescent spectra undoubtedly arise from the rare-earth dopants. It is suggested that the observed splitting of the lines attributable to the triply ionised rare-earth dopants is due to the rapidly changing crystal fields within the vicinity of a growing crack. Spectral measurements made on a natural fluorite mineral show that part, but not all, of the triboluminescent emission produced on cutting an irradiated sample may have a thermoluminescent origin.