Chromaticity Study of Yellow HTHP Lab-Grown Diamonds Based on Spectroscopy

At a Glance

Metadata	Details
Publication Date	2025-10-31
Journal	Crystals
Authors	Z. Y. Peng, Youping Sun, Mingming Xie, Zheng Zhang, Bin Meng
Institutions	Kunming University of Science and Technology
Analysis	Full AI Review Included

Technical Documentation & Analysis: Chromaticity Study of Yellow HTHP Lab-Grown Diamonds

This document analyzes the spectroscopic and colorimetric findings regarding yellow HTHP diamonds, translating the research into actionable technical specifications and material recommendations offered by 6CCVD’s specialized MPCVD diamond catalog.

Executive Summary

The research provides a quantitative framework for engineering the color and defect characteristics of nitrogen-doped diamond, directly supporting advanced applications in optics and quantum technology.

Quantitative Defect Correlation: A strong positive linear correlation (R² = 0.90) was established between the Yellowness Index (YI E313) and Nitrogen Content (Nc), providing a predictive model for color engineering.
Primary Color Mechanism: Yellow color is confirmed to be driven by Nitrogen-Vacancy (NV) centers, specifically the concentration ratio (R) of the negatively charged NV⁻ defect (637 nm ZPL) relative to the neutral NV⁰ defect (575 nm ZPL).
Material Type Confirmation: Infrared spectroscopy confirmed the samples are Type Ib diamonds, characterized by isolated nitrogen (C aggregate) defects, evidenced by characteristic absorption peaks at 1130 cm⁻¹ and 1344 cm⁻¹.
Crystallinity Assessment: Raman spectroscopy Full Width at Half Maximum (FWHM) values (ranging from 2.18 to 9.16 cm⁻¹) were used to correlate crystal quality and dislocation density with color depth.
Color Classification Standard: A new, objective three-tiered classification system (Light, Intense, Deep) was developed based on four key parameters: YI E313, hue angle (h), nitrogen content (Nc), and NV⁻ concentration ratio (R).
6CCVD Relevance: These findings are critical for 6CCVD’s clients who require precise control over nitrogen incorporation and post-growth annealing to optimize NV center density for quantum sensing and high-power optical applications.

Technical Specifications

The following hard data points were extracted from the spectroscopic and colorimetric analysis:

Parameter	Value	Unit	Context
Yellowness Index Range (YI E313)	73.63 - 99.19	N/A	Correlates directly with color depth
Nitrogen Content Range (Nc)	136.14 - 141.51	ppm	Isolated Nitrogen (Type Ib)
NV⁻ Concentration Ratio (R)	0.309 - 0.804	N/A	Ratio of NV⁻ defect in NV color centers
YI E313 vs. Nc Linear Fit	y = 0.17x + 124.40	N/A	Positive correlation (R² = 0.90)
Intrinsic Diamond Raman Peak	1332	cm⁻¹	Used for FWHM crystal quality assessment
NV⁰ Zero-Phonon Line (ZPL)	575	nm	Neutral Nitrogen-Vacancy defect
NV⁻ Zero-Phonon Line (ZPL)	637	nm	Negative Nitrogen-Vacancy defect (Key for quantum)
Isolated Nitrogen IR Peaks	1130, 1344	cm⁻¹	Characteristic of Type Ib diamond
Raman FWHM Range	2.18 - 9.16	cm⁻¹	Indicator of crystal quality (Lower FWHM = Higher Quality)

Key Methodologies

The study utilized a comprehensive suite of spectroscopic and colorimetric techniques to characterize the yellow lab-grown diamonds:

Sample Preparation: Eight yellow lab-grown diamonds (Y1-Y8) synthesized via the High-Temperature High-Pressure (HTHP) method were selected.
Photoluminescence (PL) Spectroscopy: Performed using a JASCO NRS7500 micro laser Raman spectrometer in a liquid nitrogen environment.
- Laser Source: 532 nm.
- Wavelength Range: 560-800 nm.
- Purpose: Detection and quantification of NV⁰ (575 nm) and NV⁻ (637 nm) defects.
Infrared (IR) Spectroscopy (FTIR): Conducted using a Bruker TENSOR27 FTIR Spectrometer via the reflection method.
- Wavenumber Range: 400-4000 cm⁻¹.
- Resolution: 4 cm⁻¹.
- Purpose: Identification of nitrogen aggregation state (Type Ib) and calculation of nitrogen content (Nc) using a modified formula based on 1130 cm⁻¹ and 2120 cm⁻¹ peaks.
Raman Spectroscopy: Performed using a Renishaw inVia microscope Raman spectrometer.
- Laser Source: 785 nm.
- Raman Shift Range: 100-2000 cm⁻¹.
- Purpose: Measurement of the intrinsic diamond peak (1332 cm⁻¹) and calculation of FWHM to assess crystal quality.
Colorimetry: Tested using a FUV-007 UV-Vis-NIR spectrometer via the reflection method.
- Light Source: D65.
- Observer Angle: 10°.
- Purpose: Measurement of CIELAB parameters (L*, a*, b*) to calculate Hue Angle (h) and Yellowness Index (YI E313) according to ASTM E313-20.

6CCVD Solutions & Capabilities

The research demonstrates the critical role of defect engineering (specifically NV centers and nitrogen content) in controlling diamond color and functionality. 6CCVD specializes in MPCVD growth, offering superior control over these parameters compared to the HTHP methods studied.

Applicable Materials

To replicate or extend this research for high-performance optical or quantum applications, 6CCVD recommends the following materials:

Optical Grade Single Crystal Diamond (SCD): Required for applications demanding the highest crystallinity (low FWHM) and ultra-smooth surfaces (Ra < 1nm). Ideal for creating highly coherent NV centers for quantum sensing.
Nitrogen-Doped SCD/PCD: For projects requiring controlled nitrogen incorporation (Type Ib equivalent) to maximize NV center density, allowing precise tuning of the NV⁻/NV⁰ ratio through post-growth annealing.
Polycrystalline Diamond (PCD) Wafers: Available in large formats (up to 125mm) for scaling up optical or electronic devices where large area coverage is paramount.

Customization Potential

6CCVD’s in-house capabilities directly address the needs of advanced diamond engineering:

Research Requirement	6CCVD Capability	Technical Advantage
Precise Defect Control (NV centers)	Custom MPCVD growth recipes and post-processing (annealing/irradiation).	Allows engineering of specific NV⁻/NV⁰ ratios and high-purity Type IIa substrates.
High Crystal Quality (Low FWHM)	Single Crystal Diamond (SCD) substrates up to 500µm thickness.	Achieves ultra-low dislocation density necessary for quantum coherence.
Device Integration	Custom Metalization (Au, Pt, Pd, Ti, W, Cu) services.	Enables direct fabrication of electrodes or contacts for electronic and BDD applications.
Large Area/Optical Integration	PCD plates/wafers up to 125mm diameter.	Supports industrial scaling and large-aperture optical windows.
Surface Finish	Ultra-precision Polishing (SCD: Ra < 1nm; PCD: Ra < 5nm).	Essential for minimizing scattering losses in high-power optics and ensuring reliable device bonding.

Engineering Support

The relationship established between YI E313, Nc, and NV concentration is vital for functionalizing diamond. 6CCVD’s expertise bridges the gap between gemological analysis and technical application:

Defect Engineering Consultation: Our in-house PhD team can assist researchers in optimizing nitrogen concentration and post-growth annealing parameters to achieve target NV⁻ concentrations for Quantum Sensing and Photonics projects.
Material Selection: We provide expert guidance on selecting the optimal diamond type (SCD, PCD, or BDD) and thickness (0.1µm to 10mm substrates) based on specific application requirements (e.g., thermal management, optical transparency, or electrical conductivity).

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

View Original Abstract

In recent years, lab-grown diamonds have become more popular in both domestic and international markets for their rich color palette. Research on yellow lab-grown diamonds has primarily focused on spectroscopic and defect characteristics currently, while the study has largely focused on nitrogen content and related color-causing mechanisms, such as NV series defects. However, the relationship between nitrogen content and defects and color is limited. In this study, eight lab-grown diamonds with varying yellow shades were selected as samples to be studied by photoluminescence spectra, infrared spectra, Raman spectra, and colorimetry testing. Based on the colorimetric parameters L*, a*, and b*, the standard formula for the yellowness index, the intensities of the NV0 and NV− peaks in the photoluminescence spectra and the absorptivity in the infrared spectra, the hue angle h, the yellowness index YI E313, the concentration ratio of NV− defect in NV color centers R, and the nitrogen content NC were calculated. Results indicate that characteristic peaks of NV series defects as a specific photoluminescence signature, notably the absence of [Si-V]− defect, demonstrate that the samples are high-temperature, high-pressure diamonds derived from graphite that underwent post-growth irradiation. The specific infrared signature indicates that the type of samples is type Ib, attributed to isolated nitrogen (C aggregate). The intrinsic peak of diamond is detected in Raman spectra, with symmetric stretching vibrations of C and N and the ‘D’ peak of graphite is detected as well. Meanwhile, the yellowness index shows a negative correlation with hue angle, a positive correlation with concentration ratio, and a positive linear correlation with nitrogen content, the equation y = 0.17x + 124.40. The yellowness index is divided into three levels: 70-80, 80-90, and 90-100. The yellow hue of samples is light between 70-80, intense between 80-90, and deep between 90-100.

Tech Support

Original Source

DOI: https://doi.org/10.3390/cryst15110942

References

2004 - Spectral Study of Transition Metal Ions in Colored Diamond
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2018 - Research on the Chromogenic Mechanism of Natural, Synthetic, and Processed Blue Diamonds
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2025 - Spectroscopy of green fluorescence rims on rough pink diamonds from Argyle mine [Crossref]
2020 - Discussion on the Identification of an Irradiated Green type IIa Diamond
2022 - Difference of lattice radiation damage and spectroscopic characterization in natural and artificial radiation green diamonds
2001 - Evolution and colouration of lattice defects in diamonds at high pressure and high temperature