IR stimulation spectroscopy of plagioclase and potassium feldspars, and quartz

It is known from kinetic and other studies that the differences between TL glow curves of different feldspar species are due to differences in charge trap distributions. It is reasonable to presume that stimulation spectra of different feldspar species should also differ. In an effort to determine the range of differences in the stimulation spectra of minerals useful in geochronolog ical studies, the near-IR stimulation spectra of microclines, plagioclases, quartz extracts, and feldspar-dominated extracts from sediments were measured. All samples were pretreated to ensure that only carriers evicted from thermally stable traps were involved in the luminescence process. A single stimulation peak was found in all samples. It lies at 845 nm in all microclines, most plagioclases, and all feldspar-dominated sediment extracts, and at 840 nm in two nearly pure Na plagioclases as well as all quartz extracts. 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 longer wavelengths, while increased Na content broadened it by up to 10 nm towards shorter wavelengths. The position of the peak at 845+/-0.1 nm was confirmed for plagioclase OMGB. A broad spectrum similar to that of plagioclases is found in quartz extracts, although its intensity is 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 component in all feldspars, and a common impurity substituting for Si4+ in natural quartz. For all future IRSL experiments it is suggested that LED diode stimulation is replaced by a semiconductor diode laser tuned to 845 nm.