| Metadata | Details |
|---|
| Publication Date | 2025-10-20 |
| Journal | Minerals |
| Authors | D. GIURGIU, Ion Smaranda, Adelina Udrescu, M. Baibarac |
| Institutions | University of Bucharest, Romanian Academy |
| Analysis | Full AI Review Included |
- Core Value Proposition: This research establishes a robust, combined UV-VIS-NIR and Raman spectroscopy protocol for the objective traceability and provenance attribution of natural diamonds from the Cullinan Mine (South Africa) and the Democratic Republic of Congo (DRC).
- Cullinan Spectroscopic Fingerprint: Diamonds from Cullinan are characterized by absorption bands assigned to N10, NV0, NV-, N3V0, N4V0, and N4V2 centers, frequently accompanied by a distinct vibronic structure localized between 415 and 394 nm (2.987-3.147 eV).
- DRC Spectroscopic Fingerprint: Diamonds from the DRC exhibit absorption bands attributed to N10, NV-, N3V0, N1+, and NVH centers.
- Nitrogen Concentration Differentiation: Raman scattering analysis revealed distinct nitrogen concentration ranges: Cullinan samples showed low concentrations (41 to 185 ppm), while DRC samples showed higher concentrations (204 to 336 ppm).
- Provenance Validation: Applying this combined method to 12 diamonds of unknown origin successfully assigned 83.33% (10 samples) to the Cullinan spectral profile and 16.67% (2 samples) to the DRC profile.
- Methodological Value: The simultaneous application of UV-VIS-NIR and Raman scattering provides an objective, non-destructive strategy for initial provenance assessment, narrowing down possible sources and ruling out inconsistencies.
| Parameter | Value | Unit | Context |
|---|
| Cullinan N Concentration (Range) | 41 - 185 | ppm | Calculated via Raman FWHM (Eq. 1) |
| DRC N Concentration (Range) | 204 - 336 | ppm | Calculated via Raman FWHM (Eq. 2) |
| Raman Peak Wavenumber | ~1333 | cm-1 | Characteristic vibrational mode of the cubic carbon lattice |
| UV-VIS-NIR Spectral Range | 365 - 900 | nm | Measurement range using GemmoSphere⢠|
| UV-VIS-NIR Resolution | 1.3 | nm | Spectrometer resolution |
| Raman Excitation Wavelength | 1064 | nm | YAG:Nd laser source |
| Raman Laser Power | 25 | mW | Used for FT Raman measurements |
| Raman Resolution | 2 | cm-1 | Spectrophotometer resolution |
| NV0 ZPL Transition | 575 (2.156) | nm (eV) | Zero-Phonon Line (ZPL) for neutral Nitrogen-Vacancy center |
| NV- ZPL Transition | 637 (1.945) | nm (eV) | Zero-Phonon Line (ZPL) for negatively charged Nitrogen-Vacancy center |
| N3V0 ZPL (Cape Defects) | 415 (2.987) | nm (eV) | Vibronic structure observed in Cullinan samples |
- Sample Preparation: Three distinct batches of natural diamonds were utilized: 44 from Cullinan Mine, 9 from DRC, and 12 of unknown geographical origin. Samples included both polished and rough stones.
- Microphotography: Visual documentation was performed using a SOPTOP SZMN microscope equipped with a photo/video camera.
- UV-VIS-NIR Spectroscopy: Spectra were recorded in the 365-900 nm range using a Magi Labs GemmoSphere⢠spectrometer. The system employed a 4â PTFE integrating sphere for maximum signal strength (50 scanning average, 50 ms integration time).
- UV-VIS-NIR Spectral Deconvolution: All spectra were deconvoluted using a Voigt function to accurately identify and quantify the peaks corresponding to specific nitrogen-related defect centers (e.g., N10, NV0, NV-, N3V0, N4V2, NVH).
- Raman Spectroscopy: Raman spectra were acquired using a Bruker MultiRam FT Raman spectrophotometer. Excitation was provided by a YAG:Nd laser (1064 nm wavelength) at 25 mW power.
- Nitrogen Concentration Assessment: Nitrogen concentration (N, in ppm) was calculated based on the Full Width at Half Maximum (FWHM) of the primary diamond Raman line (~1333 cm-1). Two distinct empirical equations were used, correlating FWHM to N concentration for Type Ia/Ib diamonds:
- Cullinan (Eq. 1): FWHM = 1.57 + 0.97 x 10-3 N
- DRC (Eq. 2): FWHM = 1.6 + 1.52 x 10-3 N
- Gemological Certification and Traceability: Providing objective, non-destructive verification of diamond origin, crucial for compliance with ethical sourcing standards (e.g., Kimberley Process) and consumer confidence in high-value gemstones.
- Diamond Grading and Valuation: Utilizing the unique spectroscopic fingerprints (defect centers and N concentration ranges) to confirm or dispute the claimed geographical origin, directly impacting market valuation and grading reports.
- Quantum Sensing and Computing Materials: The detailed characterization of NV0 and NV- centers in natural diamonds informs the synthesis and processing of high-purity diamond materials required for quantum applications, particularly those focusing on spin coherence and quantum memory.
- Advanced Materials Synthesis Feedback: The methodology provides a benchmark for comparing the defect profiles of synthetic diamonds (e.g., HPHT or CVD) against natural stones, aiding manufacturers in optimizing growth parameters to mimic or control specific impurity environments.
- Forensic Gemology: Establishing a database of spectral signatures linked to known geological sources to combat fraud and misrepresentation in the global diamond supply chain.
View Original Abstract
Diamond traceability has been a major challenge for the gemological industry in recent decades. In this context, this paper presents new studies using UV-VIS-NIR spectroscopy to identify the traceability and geographical origin of diamonds. The aim of the work is to identify characteristic centers of fancy-color diamonds collected from Cullinan Mine, Democratic Republic of Congo (DRC), and the geographical regions with unknown origin. Depending on the origin of the diamonds, the UV-VIS-NIR spectra can be differentiated as follows: (i) the diamonds collected from Cullinan Mine show absorption bands assigned to N10, NV0, NVâ, N3V0, N4V2, and N4V centers, which are accompanied by a vibronic structure localized between 415 and 394 nm (2.987-3.147 eV) and (ii) the diamonds from DRC show absorption bands attributed to N10, NVâ, N3V0, N1+, and NVH centers. Using Raman spectroscopy, nitrogen concentration values of diamonds collected from the Cullinan mines and DRC between 41 and 185 ppm and 204-336 ppm, respectively, were reported. We prove that the simultaneous applicability of UV-VIS-NIR spectroscopy and Raman scattering as comparative tools for assessing diamond provenance can be a valuable strategy for an initial attribution of diamonds with unknown geographical origin, knowing the optical features of diamonds collected from Cullinan Mine and DRC.
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