OPTICAL-EXCITATION OF TRAPPED CHARGES IN QUARTZ, POTASSIUM FELDSPARS AND MIXED SILICATES - THE DEPENDENCE OF PHOTON ENERGY

Optical excitation of trapped charges has been studied by stimulating them with photons of energies from 1.8 to 2.7 eV and measuring the res ulting luminescence at higher photon energies. The samples studied wer e quartz, potassium feldspar and fine-grained silicate extracts from n atural sediments. The initial luminescence intensity and its decay as the traps are emptied have been used to gain information about the tra ps contributing to the emission. For the quartz studied the data are w ell explained by excitation from a single trap. The excitation spectra for potassium feldspars and mixed silicates show evidence of two diff erent traps, the deepest of which is seen to give rise to the most lum inescence. Its optical trap-depth may be more than 2.4 eV while the de pth of the shallow trap appears to be about 2.1 eV. In nature, the dee per trap will probably not be well bleached during deposition in all a queous environments, and for optical dating of water-laid sediments se lective sampling of the shallow trap photons with energies less than 2 .3 eV for stimulation may prove beneficial.