Infrared stimulated luminescence and phosphorescence spectra of irradiated feldspars

Abstract

A new high-sensitivity wide-bandwidth 1.25–5.5 eV (225–1000 nm) spectrometer has been constructed to measure luminescence emission spectra of minerals that are of interest for optical dating. Spectra of emission resulting from 1.43 eV (IR) excitation after γ-irradiation are reported for 13 cut rock feldspars and 20 feldspar separates. Also reported are phosphorescence spectra following γ-irradiation, and after 1.4 eV excitation. The main differences between the infrared stimulated luminescence spectra and the phosphorescence is the almost complete absence of the violet, 3.1 eV, and yellow–green, 2.2 eV, bands in the phosphorescence, and the presence of a green emission band centred at 2.7 eV in the phosphorescence following γ-irradiation (but absent in the phosphorescence following 1.4 eV excitation). The red, 1.7 eV, band is present in all the phosphorescence spectra but is not always seen during 1.4 eV excitation. A band at eV is dominant in both types of phosphorescence spectra. This dependence of the luminescence spectrum on the mode of excitation suggests a strong correlation between certain traps and luminescence centres. Models involving recombination via a 'conduction band' in the traditional sense cannot account for these observations.