Trap spectroscopy and tunnelling luminescence in feldspars

Abstract

Comparative studies of tunnel luminescence, thermally stimulated luminescence (TSL), and trap energy spectra by the fractional glow technique (FGT) have been made both with sanidine and microcline feldspars. After X-irradiation at LNT these feldspars show intense tunnelling afterglow. As the temperature is raised, several TSL glow peaks may be observed, starting at 135K. An intense peak at 250K is common to all four investigated microclines. In samples of sanidine, tunnelling afterglow overcomes TSL up to 250–260K. With sanidine and microcline samples, the distributions of trap activation energies vs temperature obtained by the FGT are continuous and quasi-linear. Maxima in the trap density are observed, indicating the presence of several kinds of stable defect structures. It may be concluded that below 100K the thermally stimulated processes in the samples are frozen. Tunnelling recombination occurs between deeper localized states which are stable up to RT and higher. These results are attributed to the known ‘Al-Si order–disorder’ effect in feldspar crystals. It leads to the formation of wide continuous energy distributions of localized states. Donor–acceptor defects are caused by the association of Al3+ substituted in the centers of SiO4 tetrahedra and alkali ions in interstitial positions.