Spectroscopic characteristics of topaz: The impact of electron beam irradiation and heat treatment

Abstract

The natural topaz having the chemical formula of Al2SiO4(F,OH)(2) exhibits lots of varieties in color and composition. Most of the natural topaz has been mined in colorless. In the work we performed a spectroscopic characterization of natural colorless topaz. The samples were irradiated with 2.5 MeV and 10 MeV electrons to fluencies of 2 x 10(17) cm(-2) for 1 h and were heated at 150 degrees C and 1 h in air. From the experiments, the spectra investigated by UV-visible spectroscopy (UV-Vis), electron paramagnetic resonance (ESR), and wavelength dispersive X-ray fluorescence spectroscopy (WD-XRF). Changes in the colorless sample after irradiation resulted in brown color, which had absorption peaks at 420 and 460 nm. These samples become light blue color after subsequent heat treatment. The samples EPR lines occurred two peaks, a peak near at g = 2.012 substitutional Al3+ ion in a Si4+ site and a peak near at g = 3.5 similar to 4 substitutional Fe3+ in an Al3+ site. After irradiation, the observed that while the peak at g = 3.5 similar to 4 related EPR line are decrease, but the perk at g = 2.012 related defect line show increase.