Effects of pre-irradiation annealing at high temperature on optical absorption and electron paramagnetic resonance of natural pumpellyite mineral

摘要

Natural silicate mineral of pumpellyite, Ca_2MgAl_2(SiO_4)(Si_2O_7)(OH)_2(H_2O), point group A2/m, has been studied concerning high temperature annealing and y-radiation effects on Optical Absorption (OA) and Electron Paramagnetic Resonance (EPR) properties. Chemical analysis revealed that besides Si, Al, Ca and Mg, other oxides i.e., Fe, Mn, Na, K, Ti and P are present in the structure as impurities. OA measurements of natural and annealed pumpellyite revealed several bands in the visible region due to spin forbidden transitions of Fe~(2+) and Fe~(3+). The behaviour of bands around 900 and 1060 nm, with pre-annealing and y radiation dose, indicating a transition Fe~(2+) → eˉ + Fe~(3+). On the other hand, EPR measurements reveal six lines of Mn~(2+), and satellites due to hyperfine interaction, superimposed on the signal of Fe~(3+) around of g = 2. For heat treatment from 800 ℃ the signal grows significantly and for 900 ℃ a strong signal of Fe~(3+) hides all Mn~(2+) lines. The strong growth of this signal indicates that the transitions are due to Fe~(3+) dipole-dipole interactions.