Raman Spectroscopy Study on the Surface of High Temperature and High Pressure Diamond Crystal in Geology, Rock and Minerals
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-11-10 |
| Journal | Highlights in Science Engineering and Technology |
| Authors | Shi Li, Hui Chi, Wei Wang, Yong Yu |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Achievement: The study successfully analyzed the defect transformation and color origin in yellow High-Pressure/High-Temperature (HPHT) synthetic diamonds subjected to post-growth HPHT annealing (color fading treatment).
- Defect Transformation: HPHT treatment significantly reduced the intensity of fluorescence peaks related to NV-defects (e.g., 660 nm), while simultaneously enhancing the spectral peak related to SiV-centers (737 nm), indicating a change in defect ratios.
- Spectroscopic Signatures: Characteristic infrared absorption peaks related to C-H defects (sp3-CH2- at 2850 cm-1 and 2920 cm-1; sp2-CH2- at 1465 cm-1 and 2955 cm-1) were confirmed as common markers for HPHT synthetic diamonds.
- Identification Method: Raman spectroscopy, particularly the measurement of the width at half maximum (Phonon âlifetimeâ), is proposed as a rapid, effective method to distinguish natural from synthetic diamonds.
- Inclusion Analysis: Confocal microscopy of tiny inclusions provides critical information regarding the gemstoneâs origin (natural vs. artificially improved) and the presence of amorphous carbonaceous or graphite components (broadbands around 1420 cm-1 and 1580 cm-1).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Processing Pressure | 5 - 6 | GPa | HPHT synthesis and post-growth treatment range |
| Processing Temperature | 1500 - 1700 | °C | HPHT synthesis and post-growth treatment range |
| Heating Time | 200 | s | Duration of HPHT treatment |
| Cooling Time | 400 | s | Duration of HPHT treatment |
| Sample Size (Typical) | 3 x 3 x 1 | mm | Dimensions of analyzed samples |
| IR Scanning Range | 650 - 6000 | cm-1 | Micro-infrared spectroscopy |
| IR Resolution | 4 | cm-1 | Micro-infrared spectroscopy |
| X-ray Spectrometer Voltage | 20 | kV | Elemental analysis of inclusions |
| X-ray Spectrometer Current | 1.98 | mA | Elemental analysis of inclusions |
| Raman Excitation Lasers | 473, 532, 785 | nm | Photoluminescence and Raman testing wavelengths |
| sp3-CH2- Symmetric Stretch Peak | 2850 | cm-1 | Infrared absorption peak in HPHT synthetics |
| sp3-CH2- Antisymmetric Stretch Peak | 2920 | cm-1 | Infrared absorption peak (selected for C-H defect study) |
| SiV-Center PL Peak (Enhanced) | 737 | nm | Observed after HPHT treatment (633 nm excitation) |
| NV-Center PL Peak (Weakened) | 660 | nm | Zero-phonon sideband observed after HPHT treatment (532 nm excitation) |
Key Methodologies
Section titled âKey Methodologiesâ-
Sample Preparation and Treatment:
- Five yellow HPHT synthetic rough diamonds (H_1 to H_5) with typical cube/octahedron morphology were selected.
- Samples underwent a secondary HPHT process (5-6 GPa, 1500-1700 °C) to induce color fading by modifying nitrogen-related defects.
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Microscopic and Structural Characterization:
- Gemmological Microscopy: Used to observe internal features and growth structures.
- Diamond Observer (DeBeers): Employed ultra-short-wave UV (<220 nm) light to observe fluorescence, phosphorescence, and growth structure, crucial for identifying synthetic origin.
- X-ray Spectrometry (Thermo Scientific QUANTâX): Used to analyze the elemental composition of metallic and graphite inclusions.
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Infrared (IR) Spectroscopy:
- Micro-FTIR (Thermo Nicole tin 10MX): Used to quantify boron content and analyze nitrogen aggregation states (A set, lone atoms) and C-H defect structures (sp3-CH2- and sp2-CH2-).
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Photoluminescence (PL) and Fluorescence Spectroscopy:
- PL Spectroscopy: Performed using 532 nm and 633 nm lasers to analyze impurity elements (N, Ni, Si) and defect centers (NV0, NV-, SiV-). Spectra were normalized to the diamond Raman peak.
- 3D Fluorescence Spectroscopy: Used to map the change in fluorescence intensity as a function of both excitation and emission wavelengths, providing a comprehensive view of defect changes before and after treatment.
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Raman Spectroscopy:
- Laser Raman Spectrometer (473 nm, 532 nm, 785 nm): Used to identify genuine vs. fake gemstones based on the Raman spectrum of the diamond lattice itself.
- Phonon Lifetime Analysis: The width at half maximum of the Raman spectrum was used to infer the phonon âlifetime,â providing information on whether the gemstone is natural or synthetic.
Commercial Applications
Section titled âCommercial Applicationsâ- Gemstone Authentication and Traceability: Establishing standardized spectroscopic protocols for the rapid and effective identification of undisclosed HPHT synthetic diamonds, protecting the integrity of the natural diamond market.
- Quantum Defect Engineering: The precise control over NV- and SiV-center concentrations via HPHT annealing is directly applicable to manufacturing diamond materials optimized for quantum sensing, magnetometry, and single-photon sources.
- High-Performance Diamond Substrates: Utilizing IR and Raman analysis to monitor and control lattice defects (C-H, amorphous carbon) in synthetic diamond films and crystals used as heat sinks or high-power electronic substrates.
- Quality Control in Synthesis: Applying spectroscopic feedback (e.g., monitoring the 2920 cm-1 peak intensity) to optimize the growth parameters (catalyst, temperature, pressure) to minimize undesirable C-H defects and achieve specific color grades.
- Forensic Geology and Mineralogy: Applying Raman spectroscopy and inclusion analysis techniques to geological rock and mineral samples for high-pressure phase identification and crystal structure analysis.
View Original Abstract
This paper analyses the colour origin and colour change mechanism of high temperature and high-pressure synthetic diamonds through experiments. In this paper, ultraviolet-visible absorption spectroscopy, infrared spectroscopy, photoluminescence spectroscopy, three-dimensional fluorescence spectroscopy, laser Raman spectroscopy and X-ray rocking curve were used for analysis. The results show that it is easy to identify genuine and fake gemstones based on Raman testing of the gemstone itself. The measurement of tiny inclusions with a confocal microscope system can provide information on whether the gemstone is natural or artificially improved, and even trace the origin of the gemstone. Width at half maximum of the Raman spectrum. Phonon âlifetimeâ can provide information on whether the gemstone is natural or synthetic. The photoluminescence spectrum of gemstones can also provide valuable information about the sample. This article can also identify natural gemstones or synthetic gemstones accordingly.