An application of polychromatic UV-Vis-NIR spectroscopy on detection of beryllium treatment in ruby and yellow sapphire

Abstract

The ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy has been essentially used to characterize gem materials and their treatments. The spectrophotometer was designed using a diffraction grating to provide the monochromatic light from a tungsten lamp in analyzing a sample. The signal is recorded by a photodiode, resulting in a characteristic spectrum of a gemstone sample. While the monochromatic UV-Vis-NIR spectrophotometer is used for characterizing treated ruby and yellow sapphire samples; however, some indicative characteristic absorptions could be missing. The technique may not be able to clearly differentiate the Be-treated ruby and yellow sapphire samples from the natural ones. Therefore, polychromatic UV-Vis-NIR spectroscopy could be utilized. The polychromatic light from a tungsten lamp passing through the sample provides the polychromatic UV-Vis-NIR spectrum produced by the spectrophotometer comprising a diffraction grating with a diode array CCD or CMOS detector. Both natural and Be-treated ruby and yellow sapphire samples were measured using both spectrophotometers. The experiment reveals that the polychromatic UV-Vis-NIR excitation spectroscopy can be used to differentiate the Be-treated ruby and yellow sapphires from the natural ones. Moreover, the polychromatic UV-Vis-NIR spectrophotometer offers the advantages of portability, measuring time, and low cost.