Nitrogen Structure Determination in Treated Fancy Diamonds via EPR Spectroscopy

At a Glance

Metadata	Details
Publication Date	2022-12-07
Journal	Crystals
Authors	Ira Litvak, Avner Cahana, Yaakov Anker, Sharon Ruthstein, Haim Cohen
Institutions	Ariel University, Bar-Ilan University
Citations	2
Analysis	Full AI Review Included

Nitrogen Structure Determination in Treated Fancy Diamonds: A 6CCVD Technical Analysis

This document analyzes the research paper “Nitrogen Structure Determination in Treated Fancy Diamonds via EPR Spectroscopy” to highlight the critical role of high-quality, controlled-defect MPCVD diamond substrates in replicating and advancing defect engineering research, particularly for color centers and quantum applications.

Executive Summary

The study successfully correlated specific carbon-centered paramagnetic radicals (N1, N4, P2/W21) with the resulting color (Green, Blue, Yellow) in nitrogen-contaminated natural diamonds using a combination of irradiation and thermal annealing.

Defect Engineering: Confirmed that color enhancement relies on precise control over vacancy defect production (irradiation) and nitrogen atom orientation (annealing).
Spectroscopic Correlation: Established EPR spectroscopy as the primary tool for determining the structure of nitrogen atoms adjacent to carbon radicals, linking N4 species to blue color and N1 species to yellow color.
Material Requirement: Demonstrated that high bulk nitrogen concentration (>1000 ppm) is necessary for generating high spin concentrations (stable carbon radicals) required for effective color centers.
Process Control: Identified distinct thermal treatment protocols: Blue requires annealing at 400-600 °C (to eliminate yellow components), while Yellow requires higher temperatures (500-1000 °C) to eliminate blue components (N4 species).
6CCVD Value Proposition: 6CCVD’s MPCVD technology offers superior control over nitrogen incorporation and crystal purity compared to natural diamonds, enabling precise, reproducible synthesis of substrates optimized for advanced defect studies (e.g., NV center precursors).
Scalability: While the study used small natural stones, 6CCVD provides SCD and PCD plates up to 125mm, ensuring scalability for industrial and large-area research applications.

Technical Specifications

Parameter	Value	Unit	Context
Irradiation Energy	0.8-2	MeV	Electron accelerator (LINAC)
Annealing Temperature (Blue)	400-600	°C	Thermal treatment after irradiation
Annealing Temperature (Yellow)	500-1000	°C	Thermal treatment after irradiation
Nitrogen Conc. (Green)	>1000	ppm	High concentration Type Ia A/B
Nitrogen Conc. (Blue)	300-600	ppm	Intermediate concentration Type Ia A/B
Nitrogen Conc. (Yellow)	<200	ppm	Low concentration Type Ia A/B
Radical Conc. (Green)	2.64 x 10^-4	M	Stable carbon-centered radicals
Radical Conc. (Bulk N, Green)	2.52 x 10^-1	M	Bulk nitrogen concentration
Radical/Bulk N Ratio	3-4	Orders of Magnitude	Bulk N is higher than radical concentration
N1 Center g-Value	2.0024	Dimensionless	Correlated with Yellow color
N4 Center g-Value	2.0017-2.0022	Dimensionless	Correlated with Blue color
P2/W21 Center g-Value	2.0027-2.0035	Dimensionless	Dominant center in pretreated stones
GR1 Absorption Line	740.9 and 744.4	nm	Vacancy in neutral charge state (V°)
N3 Absorption Line	415.2	nm	Three substitutional N atoms + vacancy (3N + V)

Key Methodologies

The color enhancement protocols relied on precise control of high-energy electron irradiation followed by controlled thermal annealing (where necessary).

Material Selection: Natural Type Ia A/B diamonds were selected based on pre-treatment nitrogen contamination levels (high N for Green, intermediate N for Blue, low N for Yellow).
Irradiation (Vacancy Generation): Diamonds were exposed to high-energy electron irradiation (0.8-2 MeV) in a LINAC.
- Green Protocol: 1.5 hours of irradiation only (no thermal treatment needed).
- Blue/Yellow Protocols: 2 hours of irradiation.
Thermal Treatment (Defect Migration/Stabilization): Annealing was used post-irradiation to migrate vacancies and stabilize specific nitrogen-vacancy complexes, thereby bleaching undesired colors.
- Blue Protocol Annealing: 10-20 minutes at 400-600 °C.
- Yellow Protocol Annealing: 10-20 minutes at 500-1000 °C (higher temperature required to eliminate blue centers).
Spectroscopic Characterization:
- EPR Spectroscopy: Used to identify and quantify carbon-centered paramagnetic centers (N1, N4, P2/W21) and determine the structure of adjacent nitrogen atoms.
- FTIR Spectroscopy: Used to confirm diamond type and measure bulk nitrogen concentration (600-1500 cm^-1 range).
- UV-Vis Spectroscopy: Used to measure absorption bands corresponding to optical color centers (e.g., GR1 at 741/744 nm, N3 at 415 nm).
- Fluorescence Assessment: Used to track changes in fluorescence patterns (e.g., blue fluorescence from N impurities, strong yellow fluorescence post-annealing).

6CCVD Solutions & Capabilities

The research demonstrates the critical need for diamond substrates with precisely controlled nitrogen content and high structural integrity to enable reproducible defect engineering. 6CCVD’s MPCVD capabilities are uniquely suited to meet and exceed these requirements for advanced research and commercial applications.

Applicable Materials

To replicate or extend this research, particularly toward quantum applications (e.g., NV centers, which are N-V complexes), researchers require substrates with tailored nitrogen content and high purity.

Research Requirement	6CCVD Material Solution	Key Benefit
High N Concentration (Green/Blue analogs)	Polycrystalline Diamond (PCD)	High growth rates allow for high, uniform nitrogen incorporation (up to 1000+ ppm) necessary for high spin concentration.
Low N Concentration (Yellow/Quantum analogs)	Optical Grade Single Crystal Diamond (SCD)	Ultra-low background nitrogen (<1 ppm) enables precise, controlled introduction of N precursors for specific defect creation (e.g., NV centers).
Charge State Control	Boron-Doped Diamond (BDD)	Boron doping (Type IIb analog) allows for Fermi level tuning, critical for controlling the charge state of color centers (e.g., V⁰ vs. V^- or NV⁰ vs. NV^-).

Customization Potential

The study relied on specific irradiation and thermal treatments, which require robust, high-quality substrates. 6CCVD offers comprehensive customization services to optimize materials for these processes:

Custom Dimensions & Thickness: While the paper used small natural stones, 6CCVD provides SCD plates up to 10mm thick and PCD wafers up to 125mm in diameter. This scalability is essential for industrial color enhancement or large-area quantum device fabrication.
Surface Preparation: The study’s reliance on optical measurements (UV-Vis, Fluorescence) necessitates high surface quality. 6CCVD offers SCD polishing to Ra < 1nm and inch-size PCD polishing to Ra < 5nm, minimizing scattering losses.
Metalization Services: Although not explicitly detailed for device integration in this paper, 6CCVD offers in-house custom metalization (Au, Pt, Pd, Ti, W, Cu) for researchers planning to integrate these engineered color centers into electronic or quantum devices (e.g., electrodes for charge state manipulation).
Controlled Doping: We can synthesize diamond with specific, controlled nitrogen concentrations (ppm level) during the MPCVD growth process, providing a far more uniform and reproducible starting material than the natural Type Ia A/B diamonds used in the study.

Engineering Support

The complex correlation between nitrogen structure (N1, N4, P2/W21) and optical centers (GR1, H3, N3) requires deep material science expertise. 6CCVD’s in-house PhD team specializes in defect engineering and can assist clients with:

Material Selection: Choosing the optimal SCD or PCD grade and nitrogen concentration for specific color center or quantum defect (e.g., NV, SiV) generation projects.
Process Optimization: Consulting on pre- and post-growth treatments, including high-temperature annealing protocols, to stabilize desired defect structures (e.g., maximizing N4 for blue centers or N1 for yellow centers).
Advanced Characterization: Providing guidance on interpreting EPR, FTIR, and PL data for defect identification and quantification.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Color induction in nitrogen-contaminated diamonds was carried out via various procedures that involve irradiation, thermal treatments (annealing), and more. These treatments affect vacancy defect production and atom orientation centers in the diamond lattice. Natural diamonds underwent color enhancement treatments in order to produce green, blue, and yellow fancy diamonds. The aim of this study was to follow the changes occurring during the treatment, mainly by EPR spectroscopy, which is the main source for the determination of the effect of paramagnetic centers (carbon-centered radicals) on the color centers produced via the treatments, but also via visual assessment, fluorescence, UV-vis, and FTIR spectroscopy. The results indicate that diamonds containing high levels of nitrogen contamination are associated with high carbon-centered radical concentrations. Four paramagnetic center structures (N1, N4, and P2/W21) were generated by the treatment. It is suggested that the N4 structure correlates with the formation of blue color centers, whereas yellow color centers are attributed to the presence of N1 species. While to produce blue and yellow colors, a thermal treatment is needed after irradiation, for treated green diamonds, no thermal treatment is needed (only irradiation).

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst12121775

References

2013 - Optical Defects in Diamond: A Quick Reference Chart [Crossref]
2018 - Natural-Color Green Diamonds: A Beautiful Conundrum [Crossref]
2007 - Natural Type IA Diamond with Green-Yellow Color Due to Ni-Related Defects [Crossref]
2005 - Characterization and Grading of Natural-Color Yellow Diamonds [Crossref]
2002 - Characterization and Grading of Natural-Color Pink Diamonds [Crossref]
1978 - Investigating Artificially Coloured Diamonds [Crossref]
2002 - HPHT Synthesis of Diamond with High Nitrogen Content from an Fe3N-C System [Crossref]