Spectrofluorometer: New instrument at SSEF

Fluorescence, a form of luminescence, can occur in gemstones due to trace elements (e.g. Chromium R-lines at 693 and 694 nm in rubies), the absence of anions (F-centres) or other defects in the crystal lattice. The contribution of trace elements to the fluorescence of a gemstone is usually well understood; however, F-centres and other defects are more difficult to identify. Furthermore, the instrument allows us to study luminous substances such as fillers within gem materials. A broader description of the possibilities of spectro-fluorescence can be found in a review article by Zhang and Shen (2023).

Our instrument has an excitation wavelength range of 200 nm (deep UV) to 850 nm (NIR) and can record several fluorescence spectra over a range of different excitation wavelengths. It is also equipped with a special sample holder for solid samples, as these instruments are usually used to analyse solutions.

This enables fluorescence ‘maps’ to be recorded, providing a clearer picture of the fluorescence of gemstones. See Figure 3 for an example of a fluorescence spectrum map of a sapphire. The chromium fluorescence line at 694 nm can be seen in the spectrum map, as can the UV reaction. Additionally, the instrument can analyse luminescence lifetimes as long as they are in the millisecond time range.