Distinct ruby suite at Sardapur, Orissa: A spectroscopic investigation

Orissa is an important area for gem variety of corundum deposits in India. Spectroscopic studies, such as ESR, OAS on samples from Sardapur, Orissa, were carried out to ascertain the colour cause of corundum. Electron spin resonance (ESR) spectroscopic study was carried out on the samples to detect the presence of paramagnetic ions i.e. Fe²⁺, Fe³⁺, Ti⁴⁺, Cr³⁺ and V³⁺ etc. The variable temperature experiment carried out to observe the effect of heating on peak valence state change in paramagnetic ions. Samples were cut and polished to obtain the optical absorption spectrum (OAS) to detect the colour causing transition ions/defect centres. The samples of gem variety were step heated up to 300°C for colour enhancement studies. EPMA analysis has revealed the low chromium concentration in the rubies. The varying hues of red in the corundum are due to the presence of bivalent and trivalent iron and charge transfer process along with Cr³⁺ absorption in the 550 nm region.