A comparison of luminescence spectra and structural composition of perthitic feldspars

Abstract

Museum specimens of potassium feldspar, ranging from monoclinic orthoclase through several intermediaries to triclinic microcline, have had their structural and chemical properties characterized by optical microscopy, X-ray diffraction, X-ray fluorescence, ion microprobe and scanning electron microscopy. Thermoluminescence, radioluminescence and infra-red stimulated luminescence spectra were obtained from these samples showing two emission bands: an ultraviolet band centred around 290 nm and a broad blue band centred around 442 nm. The relative intensities of these two bands change with increasing triclinicity, with the UV band dominating in the microclines as a result of an increase in sodium exsolution features within the structure of these perthites. TL emission from the intrinsic blue peak also increases in intensity at longer wavelengths with increasing triclinicity, possibly resulting from an increase in defect sites as a result of the concentration of perthitic intergrowths of sodium lamellae.