Crystal anisotropy effects in optically stimulated luminescence of a K-feldspar

Optically stimulated luminescence of some chips of a K-feldspar was measure d as a function of the polarization angle of both the stimulating light, an d the emitted light. There were clear polarization dependencies. Optical tr ansmission spectra were also measured and a polarization dependence Found; it was, however, insufficient to account for the polarization effects obser ved in the optically stimulated luminescence. These results suggest that bo th the excitation and emission processes are themselves polarization depend ent. Both irradiated and unpreheated, and irradiated and preheated samples were measured with remarkably similar results. This suggests that both stab le and unstable components in the excitation process have the same polariza tion dependence. One explanation for all these results is that stable and u nstable traps, and the luminescence centres have preferred orientations in the crystal. Models used to compute the birefringence effects for simple di pole processes predict that the traps and luminescence centres are similarl y aligned close to either the [313] or [11 (3) over bar] directions. (C) 20 00 Elsevier Science Ltd. All rights reserved.