gems, advanced testing, inclusions, inclusion spectra, cathodoluminescence, CL

From a study of inclusions in gemstones using cold-cathode cathodoluminescence (CL) microscopy and microspectrophotometry, ten examples containing various inclusions are described. Visual microscopic examinations of the luminescing inclusions, supported by photomicrographs and spectral curves, provide valuable information about the inclusion types. Strongly luminescing, even small colourless inclusions such as apatite, fluorite, or diopside can be easily detected, though they might otherwise go unnoticed. Additional details on both inclusions and host material can be obtained through CL spectra recorded in the 380–950 nm range. Because of the limited electron penetration depth into solids, all CL investigations must be conducted where inclusions intersect the surface of a host gemstone facet. Distinct colour differences between the CL emission of host and inclusion aid in their differentiation. This method also helps distinguish between inclusions that are otherwise difficult to separate by standard optical microscopy. Cold-cathode CL is a non-destructive and rapid technique that employs commercially available instruments and requires no coating or special treatment of samples.