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

Optically stimulated luminescence of some chips of a K-feldspar was measured as a function of the polarization angle of both the stimulating light, and the emitted light. There were clear polarization dependencies. Optical transmission spectra were also measured and a polarization dependence found; it was, however, insufficient to account for the polarization effects observed in the optically stimulated luminescence. These results suggest that both the excitation and emission processes are themselves polarization dependent. Both irradiated and unpreheated, and irradiated and preheated samples were measured with remarkably similar results. This suggests that both stable and unstable components in the excitation process have the same polarization dependence. One explanation for all these results is that stable and unstable traps, and the luminescence centres have preferred orientations in the crystal. Models used to compute the birefringence effects for simple dipole processes predict that the traps and luminescence centres are similarly aligned close to either the [313] or [11-bar3] directions