Luminescence measurement of Feldspar

Abstract

In their ideal form, feldspars are wide bandgap (> 5 eV) insulators with a well-defined crystal structure. A natural sample may contain different feldspar phases, disorders, twinning effects, fractures, dislocations, and highly variable impurity contents. With such messy materials, one might expect that exposing the samples to ionizing radiation would alter the structure so that the results from a single feldspar would not be reproducible. However, one finds that the luminescence emission changes with sample temperature in a similar way for different feldspars and decays away with prolonged Infrared (IR) exposure at a similar rate. In these experiments, the luminescence intensities of irradiated aliquots of A1, K3, K6, and VI.1 were measured while they were exposed to 850 nm exciting light either for long periods at constant aliquot temperature or while the aliquot temperature was changed during the optical excitation. I found that the luminescence intensity decreased with time for all sample aliquots, and all emission bands if the optical excitation and the aliquot temperature remained constant. The decay rate for the luminescence from K3 was found to be independent of temperature, but for the other samples, it was not. Our results are consistent with a model consisting of one type of trap, and electrons excited from these traps recombine at different luminescence centers producing the different emission bands. Differences in the activation energy and work function values between our samples for the same emission band, and between our samples and those of others, are interpreted as being caused by slightly different environments around the traps and luminescence centers.