TRAP SPECTROSCOPY AND TUNNELING LUMINESCENCE IN FELDSPARS

Comparative studies of tunnel luminescence, thermally stimulated lumin escence (TSL), and trap energy spectra by the fractional glow techniqu e (FGT) have been made both with sanidine and microcline feldspars. Af ter X-irradiation at LNT these feldspars show intense tunnelling after glow. As the temperature,is raised, several TSL glow peaks may be obse rved, starting at 135 K. An intense peak at 250 K is common to all fou r investigated microclines. In samples of sanidine, tunnelling aftergl ow overcomes TSL up to 250-260 K. With sanidine and microcline samples , the distributions of trap activation energies vs temperature obtaine d by the FGT are continuous and quasi-linear. Maxima in the trap densi ty are observed, indicating the presence of several kinds of stable de fect structures. It may be concluded that below 100 K the thermally st imulated 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-disorde r' effect in feldspar crystals. It leads-to the formation of wide cont inuous energy distributions of localized states. Donor-acceptor defect s are caused by the association of Al3+ substituted in the centers of SiO4 tetrahedra and alkali ions in interstitial positions. (C) 1998 Pu blished by Elsevier Science Ltd. All rights reserved.