Optical Absorption and Electron Spin Resonance in Natural, Irradiated and Heated Spodumene

摘要

Heat treatment and X and gamma -Rays irradiation of lylac and colorless natural spodumene, LiAlSi sub 2 O sub 6 , have been studied. Irradiation produces a color change, from lylac or colorless to green. Irradiated samples heated at 200 deg C turn lylac and bleach at 400 deg C. Optical absorption spectra were decomposed into gaussian line shape bands and it is observed that green and lylac centers are simultaneously created by irradiation. These centers are independent from each other. Optical absorption, EPR and X-Ray fluorescence results show the spectra of impurities, responsible by the presence of the created centers and indicated Mn participation in the process of centers creation and destruction. Decay kinetics of green and lylac centers have been studied and it is observed that simple kinetic models do not apply to these cases. An empirical fit allowed the calculation of activation energies of the lylac and green centers decays. Discussions about the present results led us to propose a new model where the green and lylac centers are due to Mn exp 3+ ions in two different Al exp 3+ sites, whose absorption are intensified by the interaction with an electron trapped in a neighbour oxygen. (Atomindex citation 16:007883)