Optical properties of natural pyralspite garnets: The effect of electron beam irradiation

Abstract

Almandine, pyrope and spessartine garnets were investigated. The samples were irradiated with 10 MeV electron energy to fluencies of 2 x 10(17) cm(-2) for one hour. After irradiation, the Cr3+ ion absorption band decreased but the Fe2+ ion increased in the UV-visible and Fourier transform infrared (FT-IR) spectra of pyrope garnets. In the spessartine samples, the absorption bands of Mn2+ decreased but Fe2+ increased. However, there was no significant change in the almandine garnet spectra. Electron paramagnetic resonance (EPR) was used to measure the changes in the electrovalence of the pyrope and spessartine garnets after irradiation. Pyrope garnets exhibited two peaks, a peak near g similar to 1.98 attributed to Cr3+ in the octahedral position and a peak near g similar to 2.01 attributed to Fe3+ in the octahedral position. Spessartine garnets had only one peak near g similar to 2.04, attributed to Fe3+ in the octahedral position.