It was recalled that recent developments in the infrared-stimulated luminescence of feldspars had enhanced their importance for geological dating. However, this use was limited by an anomalous fading of the thermoluminescence which was attributed to tunnelling between (D-A) pairs. In the case of feldspars, this fading was very frequent and unpredictable. A systematic comparative study of the tunnelling effect in the after- glow of irradiated feldspars was made by using some 32 different well-characterized samples of feldspar crystals. All of them exhibited a low-temperature after-glow which was due to tunnelling effects in a Gaussian near-infrared band that was centered on 710nm. It was attributed to Fe3+ ions that were involved with a so-called Al-Si order-disorder of the occupation of sites in the feldspar lattice. This effect was known to the classical theory of the mineralogy and crystallography of feldspars, but had not previously been related to tunnelling luminescence. The tunnelling after-glow was concluded to be a convenient criterion for the possibility of thermoluminescence dating of feldspars.

R.Visocekas, A.Zink: Radiation Effects and Defects in Solids, 1995, 134, 265-72