Recuperation of infrared stimulated luminescence of feldspars

After bleaching the optically stimulated luminescence (OSL) signal to a low residual level, the signal has been found to increase during subsequent storage or preheating. This effect is well known in quartz as “recuperation of OSL after bleaching” (Aitken, M.J., Smith, B.W., 1988. Optical dating: recuperation after bleaching. Quat. Sci. Rev. 7. 387–393.). A better understanding of recuperation in feldspars could help the dating specialist, because this process might be different from the recuperation observed in quartz. This paper highlights a few examples of a larger study, which cannot be shown here in complete detail. We carried out a recuperation study of infrared-stimulated luminescence (IRSL) of different feldspars from a mineral collection, mainly alkali feldspars and one albite. The samples were irradiated with doses of 200, 1000 and 2500 Gy in a ⁶⁰Co gamma cell. Subsequently, the samples were stored in the dark at room temperature (3 weeks up to 6 months, depending on the applied dose), so that the very intense irradiation-induced phosphorescence can decrease for many orders of magnitude. The emitted OSL was measured through detection filters also used in dating (Schott UG 11, Hoya U 340 for detection of near UV-emissions and Schott BG 39 for detection in the visible range). Recuperation times up to 100 days were used. The recuperated-OSL emissions were measured either with the optical filters mentioned above or with a modified experimental set-up using a variable interference filter with a continuous detection range from 400 to 700 nm. In some feldspars very intense recuperation signals (up to 100% and more of the initial signal) were observed when optical stimulation was performed with IR and broadband detection using the BG 39 or when detection was carried out in the near ultraviolet region. The IRSL emissions at 410 and 560 nm, measured with the interference filter, showed no recuperation despite a clearly detectable first shine-down.