On the relationship between luminescence excitation spectra and feldspar mineralogy

Feldspar minerals can be used as naturally occurring radiation dosemeters, with dose assessment commonly using luminescence techniques. Since many feldspars contain radioactive K-40, knowledge of the mineralogy of the luminescent samples being measured is of high importance. Most feldspars contain more than trace amounts of highly luminescent Fe3+ impurities, and this article examines the relationship between features of the luminescence excitation spectrum of this ion with sample mineralogy. It is demonstrated that there is a near linear correspondence between the plagioclase feldspar composition and the separation of the T-4(2)(D) and (4)A(1)(4)E(G) Fe3+ ion levels, and this could be used to identify plagioclase feldspar composition. In the samples tested, certain features of the spectra also allowed a distinction to be made between the alkali (K-Na) and plagioclase (Na-Ca) feldspar groups. The results are compared with properties of the excitation spectra dose-dependent optically stimulated luminescence (OSL) in order to compare the chemical environment of the OSL donor defect, and the isolated Fe3+ centres.