Abstract
Oxygen vacancy is an inherent defect of aquamarine crystals. The concentration and properties of this defect have an essential influence on aquamarine crystals and optical properties. This paper reports that blue in aquamarine crystals is due to the interaction between Fe2+ and oxygen vacancy. Infrared and Raman spectra showed that more Fe2+ replaced Al3+ in dark sample A than in light sample B. Oxygen vacancies were found in all samples. Dark sample A strongly absorbed the 830 nm band associated with Fe2+ in the UV–Vis–NIR absorption spectrum. The band gap of dark sample A was smaller than that of light sample B, and the difference in band gap was related to the concentration of oxygen vacancies. X-ray Photoelectron Spectroscopy showed that the oxygen vacancy concentration in sample A was higher than that in sample B, which showed that the oxygen vacancy concentration affected the color depth of aquamarines.
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