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Laser Induced Breakdown Spectroscopy (Libs) in Gemology

Abstract paper presented by Ted Themelis at the International Gemmological Conference in Wuhan, China
September 2004

This work presents a preliminary study dealing with the detection of elements in gems using the Laser Induced Breakdown Spectroscopy (LIBS) method. The purpose of this project was to investigate the overall performance of the LIBS method for detecting beryllium (Be), lithium (Li) and boron (B) in untreated and treated rubies-sapphires, as well as chrysoberyls and beryls. Most of these corundums were heated by the author with/without beryllium, lithium in his thermo-chemical lab in Bangkok.

Ted Themelis

Ted Themelis working with LIBS in the U.K.

The elements analyzed in these specimens were performed with a bench-type LIBS configuration setup. Laser sparks fired into the surface of the specimens by focused pulses from a laser produced plasma with distinct spectral emission signatures which were captured by a spectrometer and processed by a computer. All observations and testing procedures were recorded. The ionic emission lines of Be, Li and B as well as the atomic lines of Al were detected and numerous spectrograms were produced. Detection limits of Be, Li and B in corundum, damage assessment of the specimens, measurement parameters, laser energy, signal interference, calibration, and other issues were investigated.

The results of this study showed that the LBS method can detect Be, Li, B and other elements in corundum. Based on the number and quality of the specimens tested the following observations were made:

  1. Qualitative measurements tolerance of error was ~20%.
  2. Quantitative measurements could not be achieved.
  3. Detection limits of beryllium in corundum was determined ~3 to 4 ppm.
  4. Calibration curve for beryllium in corundum could not be produced.
  5. Calibration using master samples Be-treated and Li-treated corundums is possible, but limited.
  6. The LIBS method was termed “slightly destructive” for gemological testing.

In conclusion, the LIBS method used as a tool for detection of Be, Li, B and other elements in corundum and other gemological investigations is strongly indicative, but not conclusive. The current generation of the LIBS instrumentation will not replace the well-established LA-ICP-MS and SIMS methods.

It is emphasized that this study is a preliminary account of the applications of LIBS in gemology and verification of the facts uncovered in this investigation must be substantiated with future experiments and research.

 


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