PULSED PHOTOSTIMULATED LUMINESCENCE OF ALKALI FELDSPARS

The use of pulsed photostimulation techniques has a number of practica l and conceptual attractions compared with continuous stimulation appr oaches. Enhanced signal-to-background ratios, opportunities for signal recovery techniques, and ability of detecting luminescence asynchrono usly and close to stimulation wavelengths are all of practical interes t. In addition, it is possible to measure the time-scale and underlyin g physical processes of the charge transport and luminescence recombin ation steps following photostimulation. Proximity effects (localized t ransitions, tunneling) and re-trapping can be detected directly. Facil ities for pulsed photostimulated luminescence measurements using light -emitting diode (LED) arrays, laser diodes and a pulsed dye laser, wit h time-domain analysis down to 10(-8) s have been developed. These fac ilities are described, together with results from studies of natural a nd laboratory induced signals from alkali feldspars measured at variou s times after irradiation. For the first time it has been shown that t he recombination dynamics of irradiated feldspars consist of a complex series of continua and line components, presumed to be associated wit h distinct charge transport processes between traps and recombination sites. Evidence of post-irradiation modification of recombination dyna mics is presented for a series of highly irradiated International Atom ic Energy Agency (IAEA) F1 feldspar samples, and for a volcanic lava e xhibiting gross short-term fading of both thermoluminescence and photo stimulated luminescence. This provides direct evidence that fading is associated with short-range processes between trap and centre and, als o for the first time, suggests an effective physically based means of detecting and potentially remedying such behaviour in dating studies.