A Comparison of R-line Photoluminescence of Emeralds from Different Origins

Mar 1

Attractive gem-quality emeralds are sourced from several world localities, and gemmological labs are often asked to identify their origin and sperate them from synthetics. R-line PL spectroscopy can help address these challenges. This rough-and-cut … — Attractive gem-quality emeralds are sourced from several world localities, and gemmological labs are often asked to identify their origin and sperate them from synthetics. R-line PL spectroscopy can help address these challenges. This rough-and-cut pair of emeralds from Colombia show the saturated green colour that is prized for stones from this locality. The crystal, known as El Itoco, weighs 94.4g. Composite photo by Bilal Mahmood.

A fundamental task for gemologists is determining whether an emerald is natural or synthetic. Within the laser-excited photoluminescence spectrum of emerald, the peak positions and relative intensities of two emissions in the 680-685 nm range, known as R lines, can help identify if a sample is natural and can also provide information about its geological origin. In particular, the R line synthetic emerald is positioned at the shortest wavelength, while for natural emeralds with a non-schist origin this line is found at the same or longer wavelength. This measurement can supplement origin results obtained from established methods, such as inclusion microscopy, spectroscopy (e.g. ultraviolet-visible-near infrared [UV-Vis-NIR], Fourier-transform infrared [FTIR] and Raman} and trace-element analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS).

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