IR STIMULATION SPECTROSCOPY OF PLAGIOCLASE AND POTASSIUM FELDSPARS, AND QUARTZ

It is known from kinetic and other studies that the differences betwee n TL glow curves of different feldspar species are due to differences in charge trap distributions. It is reasonable to presume that stimula tion spectra of different feldspar species should also differ. In an e ffort to determine the range of differences in the stimulation spectra of minerals useful in geochronolog ical studies, the near-IR stimulat ion spectra of microclines, plagioclases, quartz extracts, and feldspa r-dominated extracts from sediments were measured. All samples were pr etreated to ensure that only carriers evicted from thermally stable tr aps were involved in the luminescence process. A single stimulation pe ak was found in all samples. It lies at 845 nm in all microclines, mos t plagioclases, and all feldspar-dominated sediment extracts, and at 8 40 nm in two nearly pure Na plagioclases as well as all quartz extract s. Microclines showed the narrowest spectrum, with a 0.127 eV (similar to 80 nm) FWHM. Peak width of oligoclases was 0.138 eV (88 nm) FWHM. Increased Ca content broadened the peak by similar to 5 nm towards lon ger wavelengths, while increased Na content broadened it by up to 10 n m towards shorter wavelengths. The position of the peak at 845+/-0.1 n m was confirmed for plagioclase OMGB. A broad spectrum similar to that of plagioclases is found in quartz extracts, although its intensity i s lower by 1 to 2.5 orders of magnitude from that of feldspars. It is suggested that the stimulation spectrum is due to an Al3+ (alkali)(+) complex, which is a major (similar to 25% by weight) structural compon ent in all feldspars, and a common impurity substituting for Si4+ in n atural quartz. For all future IRSL experiments it is suggested that LE D diode stimulation is replaced by a semiconductor diode laser tuned t o 845 nm.