EPR and Optical Spectroscopy of Impurities in Two Synthetic Beryls

Abstract

Two synthetic beryls (Al2Be3Si6O18) of different color (purple and blue-green) were studied with electron paramagnetic resonance (EPR) and optical spectroscopy. In both crystals, the known spectra of Cu2+ and Fe1+ were observed with the same relative intensity. In the purple sample heated at 700°C in hydrogen atmosphere, two different kinds of Mn2+ EPR spectra were observed. The main one is pseudoaxial, it arises from ions substituted for Al3+ at position 4c of the structure. The weaker one is more complex, it has orthorhombic symmetry and is characterized by an unusually large zero-field splitting (B2 0 = 741 · 10-4 cm-1) and an isotropic hyperfine constant A = 70 G. This spectrum arises from Mn2+ at position 6f in the structure, normally occupied by Be. From optics, the blue-green color arises from Cu2+, while the purple one is due to Mn3+.