Three-dimensional thermoluminescence spectra of feldspars

The paper describes a systematic study of the thermoluminescence emission spectra of thirty feldspars covering the whole composition range from high potassium (orthoclase) through high sodium (albite) to high calcium (anorthite). The study was stimulated by the need to understand the properties of feldspars in connection with the application of thermoluminescence to the dating of sediments. The data were obtained with a high-sensitivity Fourier transform spectrometer, which allows measurements at the low light levels found in natural samples. Three-dimensional displays in which intensity is plotted as a function of photon energy and temperature assist identification of a wide range of spectral features. A number of common features are found: an emission at 3.1 eV is strong in alkali feldspars with more than 80 mole.% orthoclase and occurs with lower intensity in most other alkali feldspars and some plagioclases; a broad band with a flat maximum near 2.6 eV is found in all alkali feldspars at temperatures near 200 degrees C when artificially irradiated, and at higher temperatures in some natural samples. Emission at 2.2 and 4.4 eV is characteristic of plagioclases with more than 75 mole.% of albite. Plagioclases with more than 50 mole.% anorthite, and alkali feldspars with less than 50 mole.% orthoclase, emit mainly in the range 1.5-2 eV. These features can be identified with luminescence centres suggested by previous workers. The application to practical thermoluminescence dating is discussed.