CVD Diamond Detection: Deep Diagnostic Reference
Full detection protocol for CVD synthetic diamonds, distinguishing from natural and HPHT-treated stones using DiamondView, FTIR, and photoluminescence.
CVD Growth Process
Chemical Vapour Deposition (CVD) grows diamond from a carbon-bearing gas plasma
(typically CH₄/H₂) at low pressure (~100 torr) and ~700–1000 °C, building up the
crystal in columnar striated layers rather than the octahedral sectors of natural
diamond formation. CVD diamonds are typically Type IIa (near-nitrogen-free) and
colourless to light brown; residual brown colour is often removed by a secondary
HPHT annealing step, which can suppress certain CVD markers and complicate detection.
The key diagnostic instruments are DiamondView (225 nm SW UV imaging) and
photoluminescence spectroscopy at 77 K: DiamondView reveals characteristic orange-red
phosphorescence and columnar growth threads absent from natural and HPHT synthetic
diamonds [1], while PL at 77 K detects the silicon-vacancy
(SiV⁻) doublet at 736.9/736.6 nm, a growth-chamber artefact absent in natural stones
[2]. CVD diamond is clearly distinguishable by absorption,
photoluminescence, and cathodoluminescence spectra [3].
Disclosure as "synthetic diamond" is mandatory under all governing standards.
Key CVD Growth Features
| Feature | Description | Origin |
|---|---|---|
| SiV⁻ doublet at 736.9/736.6 nm (PL) | Silicon-vacancy centre from Si contamination in growth chamber; seen in PL at 77 K [2] | Growth artifact (trace Si in plasma) |
| Columnar/striated growth pattern (DiamondView) | Threads and bundles perpendicular to growth direction; step-flow mechanism produces layered striae | CVD layer growth architecture |
| Orange-red phosphorescence (DiamondView, 225 nm) | Characteristic phosphorescence not seen in natural diamond or HPHT synthetics (Zhang et al. 2024) | NV⁻ related; step-flow growth contribution |
| NV centres NV⁻ (637 nm) / NV⁰ (575 nm) | Present in most CVD stones; ratio may differ from HPHT-treated natural diamonds | N-vacancy pairs in Type IIa lattice |
| Type IIa FTIR signature | No N absorption >5 ppm; NV-H (NVH⁰) at 3123 cm⁻¹ in some samples | Near-nitrogen-free growth environment |
| Anomalous birefringence | Uniform or banded strain from columnar growth; distinct from natural plastic deformation patterns | Growth stress in CVD layers |
Detection Methods: Full Protocol
| Method | Finding | Reliability | Notes |
|---|---|---|---|
| LWUV fluorescence (365 nm) | Variable: inert, orange, or blue depending on post-growth HPHT annealing; anomalous uniformity across the stone | Preliminary screening | Cannot confirm CVD alone; triggers lab testing |
| SWUV fluorescence | Often strong and uniform; lacks the sector fluorescence pattern of HPHT natural diamonds | Indicative | Supports but does not confirm CVD |
| DiamondView (225 nm SW UV imaging) | Orange-red phosphorescence (diagnostic when present); columnar/striated growth with no octahedral sectors; distinct from HPHT cross-hatched sectors | Most diagnostic single test | Zhang et al. 2024 is the primary reference for the phosphorescence claim |
| FTIR | Type IIa signature (N <5 ppm); NV-H absorption at 3123 cm⁻¹ in some CVD samples with N doping | Instrument test | Distinguishes Type IIa; necessary but not sufficient for CVD identification alone |
| Photoluminescence at 77 K | SiV⁻ doublet at 736.9/736.6 nm, characteristic of CVD origin; rarely in natural or HPHT-treated stones; NV⁰ (575 nm) and NV⁻ (637 nm) also present | Gold-standard lab test | SiV⁻ doublet is the most specific CVD marker in PL |
| UV-Vis absorption | Type IIa spectrum; possible 270 nm band if N-doped during growth | Supporting | Consistent with Type IIa; not CVD-specific |
CVD vs HPHT Synthetic vs Natural: Comparison
| Property | Natural Type Ia | Natural Type IIa | HPHT-Treated Natural IIa | CVD Synthetic | HPHT Synthetic |
|---|---|---|---|---|---|
| FTIR N content | >100 ppm N (aggregated) | <5 ppm N | <5 ppm N | <5 ppm N (as grown) | Variable N (type Ib to IIa) |
| LWUV fluorescence | Blue N3 (most stones) | Weak/inert | Inert (typical) | Variable | Variable |
| DiamondView pattern | Octahedral growth sectors | Weak/irregular | Cross-hatched green sectors | Columnar/striated threads | Cuboctahedral sectors |
| DiamondView phosphorescence | Rare | Rare | Variable | Orange-red (diagnostic) | Variable |
| PL SiV⁻ 737 nm | Absent | Absent | Absent | Present (most stones) | Absent |
| PL NV⁻/NV⁰ ratio | Varies with type | Varies | High NV⁻ (treated) | High NV⁻ | Varies |
Secondary HPHT Complication
Some CVD diamonds undergo a secondary HPHT step to remove residual brown colour
(a common by-product of CVD growth). This can:
- Suppress or modify the SiV⁻ centre (reduces reliability of this marker)
- Change the LWUV fluorescence response
- Produce a DiamondView pattern that combines CVD columnar striations with HPHT-like
modification of the fluorescence
Expert laboratory testing is required when HPHT-annealed CVD is suspected. The columnar
growth architecture is typically still visible in DiamondView even after secondary HPHT.
Disclosure and Stability
- Disclosure: mandatory as "synthetic diamond" or "laboratory-grown diamond" per all
governing bodies; "cultured" or "cultivated" are not acceptable per CIBJO - GIA, Gem-A, SSEF: do not grade as natural; issue separate synthetic grading reports
with laser-inscribed "LG" notation - Stability: as a diamond, physical and chemical durability is identical to natural;
colour treatment (if HPHT-annealed) is permanent
References
- ↑ 1. Zhang, Y. (2024). DiamondView Luminescence and Phosphorescence of CVD Synthetic Diamonds. Crystals, 14(9). DOI: 10.3390/cryst14090804.
- ↑ 2. Eaton-Magaña, S. (2017). An Introduction to CVD-Grown Synthetic Diamond. Gems & Gemology, 53(3). DOI: 10.5741/gems.53.3.262.
- ↑ 3. Martineau, P. (2004). Identification of Synthetic Diamond Grown Using Chemical Vapor Deposition (CVD). Gems & Gemology, 40(1). DOI: 10.5741/gems.40.1.2.