Bleaching of blue light stimulated luminescence of quartz by moonlight
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Bleaching of blue light stimulated luminescence of quartz by moonlight H M RAJAPARA1,2,* , VINAYAK KUMAR1, NAVEEN CHAUHAN1, P N GAJJAR2 and A K SINGHVI1 1 AMO-PH 2
Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India. Department of Physics, Electronics and Space Science, University School of Sciences, Gujarat University, Ahmedabad 380 009, India. *Corresponding author. e-mail: [email protected] MS received 13 December 2019; revised 27 June 2020; accepted 9 July 2020
Moonlight is sunlight reCected from the moon’s surface. It is additionally modulated by the Earth’s atmosphere, dust and pollutants on its way to the surface of the Earth. This contribution reports the bleaching rates of blue light stimulated luminescence (BLSL) signal of Quartz under full moonlight exposure at the Earth’s surface. Quartz BLSL reduced to 70% by an exposure of 5 hrs moonlight, is in contrast to *90% reduction in \ 3 s with daylight. This was anticipated due to (a) reduced moonlight Cux by about a factor of half a million (Agrawal in Lat. Am. J. Phys. Educ. 4(2):325–328, 2010; J. Phys. Astron. 5(1):1–15, 2017); (b) inverse power law dependence of bleaching eDciency on wavelength (Spooner in The validity of optical dating based on feldspar, Ph.D. Thesis, Oxford University, Oxford, 1993; Chen and McKeever in Theory of Thermoluminescence and related phenomena, World ScientiBc Publications, London, 1997, Chen and Pagonis in Thermally and optically stimulated luminescence: A simulation approach, Wiley and Sons, Chichester, 2011); and (c) moonlight and daylight have spectral peaks around 650 and 550 nm, respectively. Deconvolution of OSL components suggests that moonlight aAects the fast component of OSL signal the most. This has ramiBcation for the application in polar regions, where the availability of daylight is at a premium during the winter months. Within a given context, it is conjectured that this could be used to infer the seasonality of sediment transport. Keywords. Blue light stimulated luminescence (BLSL); moonlight bleaching; daylight bleaching; luminescence dating.
1. Introduction Optical bleaching of quartz and feldspar luminescence depends on the intensity and spectrum of light and the duration of exposure along with the luminescence behaviour of individual mineral grains of sand and their grain size (Godfrey-Smith et al. 1988; Jain et al. 2003). While considerable eAorts have been expended in understanding the bleachability of luminescence signal under daylight
exposures (Singhvi et al. 1982; Aitken 1985, 1998; Sohbati et al. 2017), only limited (possibly one) studies have been carried out on bleaching from the nightlight/moonlight. This study reported that 3 hrs of exposure to nightlight in Sweden comprising moonlight and city lights bleached the BLSL signal of Quartz by up to 40% (Lindvall et al. 2017). Despite the obvious simplicity, experimental data on the rate and extent of bleaching of blue light stimulated luminesce
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