Seven portable Raman spectrometers, EnSpectr RaPort Handheld Analyzer among them, equipped mainly with 785- and 532-nm excitation lasers were used in a comprehensive investigation of a series of beryl varieties with the accent on emeralds.
“RaPort the sequentially shifted excitation Raman spectrometer, allow recording excellent quality Raman spectra comparable with laboratory dispersive Raman microspectrometers.”
“RaPort had the unique opportunity to be able to record Raman bands of high wavenumbers…”
By the number of beryl spectrum bands located at right positions as well as low amount of noise, fluorescence and artefacts RaPort showed the best performance. “Additionally, this instrument operates on the spectral range of up to 4000 cm-1, which is unique among the tested instruments and allows for identification of OH stretching vibration of water molecules in channels in the beryl structure.”
Very good quality spectra of the aquamarine sample were also provided by RaPort.
A major part of the study involved “determination of accuracy of the tested portable Raman spectrometers, i.e. how much the wavenumber values of recorded Raman bands of beryl samples differ from the reference values.”
Portable Raman spectrometers generally have inferior performance in comparison to the laboratory instruments, and while the impact of orientation of the crystal generally has a strong effect on the Raman spectra, several minor changes in the spectra might be a challenge for the miniaturized Raman instruments.
Moreover, RaPort enabled to observe interesting nuances such as changing intensities of the two very closely located bands: at about 1000 and 1010 cm-1.
Studies were also made of ‘the spectra obtained with the instrument RaPort, the only one whose spectral range includes the OH stretching band.” In all the 13 samples in question, when the position of the 1070 cm-1 band was comprised between 1068 and 1069 cm-1, the bandwidth was 20 cm-1 or less.
“Besides carbon dioxide, other small molecules are often trapped in the channels, most frequently the water molecules. And indeed, this is documented by the strong Raman signal in the O─H stretching region (3605 cm-1) in the spectra obtained with the instrument RaPort.”
“A series of portable Raman instruments tested in the frame of this study can be considered as an interesting collection of modern analytical tools to mainly be dedicated for an out-of-lab deployment. This is for the first time that experience obtained to evaluate the possibilities and limits for mineralogical work of seven individual instruments was collected. All the instruments tested can be used for common gemmological and mineralogical work – Raman spectra recorded contain the strongest features at correct expected positions. By this way, the instruments allow unambiguous identification of gemstones (here beryls). Very small instruments allow easy handling and highest portability seem to allow recording excellent quality Raman spectra with band positions and intensities comparable with laboratory dispersive microspectrometers.”