Microwave spectroscopy as a potential tool for color grading diamonds

Yossi Rabinowitz, Ariel Etinger, Asher Yahalom, Haim Cohen, Yosef Pinhasi

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


A diamond’s color grading is a dominant property that determines its market value. Its color quality is dependent on the light transmittance through the diamond and is largely influenced by nitrogen contamination, which induces a yellow/brown tint within the diamond, as well as by structural defects in the crystal (in rare cases boron contamination results in a blue tint). Generally, spectroscopic instrumentation (in the infrared or UV–visible spectral range) is used in industry to measure polished and rough diamonds, but the results are not accurate enough for precise determination of color grade. Thus, new methods should be developed to determine the color grade of diamonds at longer wavelengths, such as microwave (MV). No difference exists between rough and polished diamonds regarding stray light when the MW frequency is used. Thus, several waveguides that cover a frequency range of 3.95–26.5 GHz, as well as suitable resonator mirrors, have been developed using transmission/reflection and resonator methods. A good correlation between the S12 parameter and the nitrogen contamination content was found using the transmission/reflection method. It was concluded that electromagnetic property measurements of diamonds in the MW frequency range can be used to determine their nitrogen content and color grading. The MW technique results were in good agreement with those obtained from the infrared spectra of diamonds.

Original languageEnglish
Article number3507
Issue number12
StatePublished - 2 Jun 2021
Externally publishedYes

Bibliographical note

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.


Funding: This research was funded by the Israeli Ministry of Economics through the KAMIN program, and the authors wish to acknowledge this assistance.

FundersFunder number
Israeli Ministry of Economics


    • Dielectric measurements for materials
    • Measurement techniques
    • Spectroscopy
    • Spectrum analysis


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