Infrared luminescence of Pb+ centres in potassium-rich feldspars

This paper reports on new results of the characteristics of photo- and radioluminescence emissions at 865 nm and 910 nm emitted by potassium-rich feldspars (KAlSi3O8). For the physical interpretation of its behaviour, the IR luminescence in potassium-rich feldspars is compared to a well investigated IR luminescence occurring in lead-doped potassium chloride (KCl:Pb) and to a study on the IR luminescence of lead-rich KAlSi3O8 (amazonite). The emissions in both materials, potassium-rich feldspar and potassium chloride, are most likely due to electron transitions in Pb+ from the 7(2)P(1/2) and 7(2)S(1/2) excited states to the 6(2)S(1/2) ground state of Pb+. Pb+ originates from interaction processes of Pb2+ cations, substituted for K+ cations in the tetrahedral feldspar framework or the cubic lattice of KCl, with ionising radiation (Pb2+ + beta, gamma, . . . --> Pb+). Another result of the experiments reported is the fact, that this radiatively induced conversion is reversed by thermal treatment of the minerals (Pb+ + T --> Pb2+). Also, the Pb+ centres can be "optically bleached", which is also interpreted as reversed conversion Pb+ + (h) over bar omega --> Pb2+. The conclusions of this paper have important implications for the physical precision of a recently developed luminescence dating method for the determination of the deposition time of Quaternary sediments using the infrared radiofluorescence (IR-RF) of potassium-rich feldspar grains. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.