Optical spectroscopy and high pressure on emeralds: synthetic and natural

Emerald, natural and synthetic, are the subject of study by means of optical spectroscopy techniques. Particularly, natural emeralds have been considered as a gemstone in jewelry not being so the synthetic ones. But, in general, the properties of these are very good for applications, for instance as a laser system, due to the impurities control. In this work a comparison between the optical properties of natural and synthetic emeralds is done. Chromium ions are the main responsible for the characteristic fascinating green color of these gemstones, entering in the crystals in octahedral sites. Absorption at room temperature shows up two broad bands in the visible region and two narrow bands called the R-lines. That spectrum corresponds to trivalent chromium ions in an octahedral site, as it happens in ruby and alexandrite. On other hand, photoemission for these materials arises in the range 640-850 nm. at room temperature. In this work it is shown that the luminescence spectra presents important changes for both type of samples as a function of the temperature and pressure; being the crystal field intensity higher for synthetic emeralds with the corresponding blue shift in the spectrum. The effect of a high pressure, applied on small samples of emerald, on the main luminescence peak shows a linear behavior.