TUNNEL AFTERGLOW, FADING AND INFRARED-EMISSION IN THERMOLUMINESCENCE OF FELDSPARS

Anomalous fading of TL, OSL and IRSL has been observed in many samples of feldspars and attributed to the tunnel effect. Investigations do show expected tunnel afterglow except for samples with no fading. Its intensity, quite noticeable at LNT, is in proportion with reported rate of fading. The emission is entirely in the red and infrared part of the spectrum. An important thermal quenching is observed. Low temperature storage results in fading of TL. Cathodoluminescence emission spectra, monitored from 200 to 900 nm, do confirm TL observations. They show two well-separated ranges: one, ''blue'', from UV to yellow (the only one observed in usual TL dating), displays various emission bands; the other, ''IR'', red and infrared, shows a well-characterized narrow Gaussian emission band, with a maximum around 720 nm. Models are proposed, relating fading with disorder in crystals. Tunnel afterglow appears as a good criterion of fading in feldspars.