UV optical absorption spectra analysis of beryl crystals from Brazil

The spectral decomposition analysis was applied to the optical absorption spectra of green and colorless beryl crystals from the Brazilian Eastern Pegmatitic province in the natural state, submitted to heat treatment and irradiated with UV light. The attributions of the lines were made taking into account highly accurate quantum mechanical calculations. The deconvolution of the green beryl spectra revealed four lines, two of them around 12,000 cm−1 (1.5 eV) and two of them around 34,000 cm−1 (4.2 eV) attributed to Fe2+ and Fe3+, respectively. The deconvolution of the colorless beryl spectra without any treatment, after heating and for the same heat treatment followed by UV light irradiation revealed five lines. The analysis of ratio relations showed that the lines at 36,400 cm−1 (4.5 eV) and 41,400 cm−1 (5.1 eV) belongs to a single defect attributed to a silicon dangling bond defect (Si:). Discussions and comparison with reported defects in quartz have supported the allocation of the lines at 61,000 cm−1 (7.6 eV) and 43,800 cm−1 (5.4 eV) to diamagnetic oxygen vacancy defect (Si–Si) and unrelaxed (Si⋯Si) defect, respectively. Finally, the line at 39,100 cm−1 (4.8 eV), quite polarized along the c-axis, was attributed to a (Fe2+OH−) defect in the structural channels.