Radiance properties of corundum and feldspar minerals under X-ray induced luminescence

Abstract

The paper reports the characteristics of luminescence spectra under X-ray excitations of corundum (sapphire and ruby) and feldspar (amazonite and labradorite) group to identify the natural gemstones. Compositional, structural and optical properties were investigated to confirm gemstones' identification. The structural studies of both blue sapphire and ruby using XRD technique showed a single phase of α-Al2O3 structural. While the amazonite and labradorite reveal the mixed-phase of microcline and plagioclase phase, corresponding to the Al2O3 and SiO2, which are the primary element composition of feldspar mineral confirmed by EDXRF studies. The optical absorption spectra were investigated in the ultraviolet and visible regions from around 300 to 1000 nm. The X-ray induced luminescence (XIL) spectra of corundum observed that the luminescence arises from Cr3+ transition in both blue sapphire and ruby, showing the narrow and intense red emission (693 nm). Meanwhile, blue sapphire's emission spectrum arises from both Cr3+ and Ti3+ transitions. The XIL spectra of feldspar centered at 446–472 nm have generally been attributed to recombination at an intrinsic defect Al–O--Al center whereas, the longer wavelength emissions spectra at around 560, 736–755 and 885 nm have been associated unequivocally with the presence of Mn, Fe and Pb impurity, respectively. This research shows that a complete characterization of blue sapphire, ruby, amazonite and labradorite stones can be successfully achieved through XIL technique, which is a fast process and non-destructive. Accordingly, XIL technique is a reliable tool for characterizing the corundum and feldspar minerals.