Luminescence Imaging and Growth Patterns

A spectrum from a single point tells us what was measured at a particular location. A luminescence image adds a second dimension: it shows where the emission is located and how it is distributed through the stone. This spatial information is one of the most important reasons fluorescence and phosphorescence imaging have great value in modern diamond identification.

It is not, however, a photographic version of a simple “natural or laboratory-grown” test. The image depends on excitation, filters, exposure, orientation, facets, detector, and the stone’s actual defect architecture. A growth pattern can be a powerful layer of evidence, but it must be interpreted together with spectroscopy, microscopy, and other relevant data.

Point analysis and a spatial map are not the same

In a point PL measurement, the detector samples a limited volume of the stone. If defect concentration varies from zone to zone, a single point may be representative only of the local area.

Imaging instead provides a map of relative emission across a larger part of the visible surface. This map may reveal:

• growth zones;
• different growth sectors;
• boundaries between growth runs;
• dislocation networks;
• zones with different defect concentrations;
• areas modified by subsequent processing;
• artifacts associated with facets, the setting, or image saturation.

Therefore, a point spectrum and an image are not competing methods. One provides spectral detail, the other spatial organization.

[VISUAL 71.1: Point PL versus a spatial luminescence map of the same diamond]

Excitation is part of the result

There is no “diamond luminescence” independent of measurement conditions. The result depends on the excitation source, the wavelengths the detector receives, the filters used, and the duration of signal integration.

Deep-UV systems are particularly useful because very short-wavelength excitation can emphasize growth and defect patterns that are not equally visible under ordinary UV observation. DiamondView is a particular commercial system of this kind; the name must not be used as a generic synonym for all UV imaging.

A professional record accompanying the image should therefore identify at least:

• the type of excitation;
• the relevant filter or detection band;
• stone orientation;
• approximate exposure or acquisition mode when relevant;
• whether the image represents fluorescence, phosphorescence, or a combined display.

Natural diamonds do not have one single pattern

A natural diamond is not defined by a single “natural fluorescence pattern.” Its growth may involve multiple episodes, octahedral and cuboid components, resorption, deformation, dislocations, and different concentrations of defects.

In many natural diamonds with octahedral growth, deep-UV may reveal concentric or layered geometric zones. Other natural diamonds may display curved cuboid horizons, irregular patterns, dislocation networks, or a complex combination of multiple structures.

The absence of a “textbook” natural pattern is therefore not in itself evidence of laboratory-grown origin.

HPHT-grown: sectoral growth as an important clue

HPHT growth often develops clearly organized growth sectors related to different crystallographic faces. Different sectors may incorporate different concentrations of nitrogen, boron, and other defect-related components, so spatially separated emission zones may appear under deep-UV excitation.

Classic cuboctahedral or cross-shaped patterns are highly useful when clearly developed. However, an “HPHT pattern” is not a universal template. Production conditions, color, clarity, post-growth treatment, and the orientation of the faceted stone can alter what is visible.

CVD-grown: layers and growth interruptions

CVD material often preserves evidence of growth in layers. A luminescence image may reveal:

• parallel or slightly curved growth bands;
• boundaries between successive growth runs;
• emission changes associated with changes in gas chemistry or defect concentration;
• dislocation zones;
• growth surfaces that intersect facets at different angles after cutting.

Such patterns can be highly diagnostic. More recent GIA populations, however, show that some modern CVD diamonds do not display a traditionally recognizable CVD pattern and may resemble certain natural type II diamonds in luminescence. Correlation with PL, FTIR, or more advanced spatial methods is then necessary.

[VISUAL 71.2: Conceptual comparison of natural-growth, HPHT-sector, and CVD-layered patterns]

Luminescence color does not identify the growth method

Blue, green, orange, or red emission is not in itself a label of natural, HPHT, or CVD origin. The same broadly perceived color may arise from different combinations of defect centers, concentrations, and excitation conditions.

One therefore does not conclude:

“red = CVD” or “blue = natural.”

The relevant combination is:

emission color + spatial pattern + emission duration + spectroscopic context + other gemological data.

Post-growth treatment can change emission

HPHT annealing or other post-growth processes can alter the concentrations and balance of defect centers, so luminescence color or intensity after processing may differ substantially from the as-grown state.

The important consequence is:

Treatment can change luminescence contrast, but it need not erase the geometric memory of growth.

In documented CVD examples, dominant emission changes after HPHT processing, while the layered growth structure and certain dislocation features remain recognizable.

A growth zone, color zone, and strain are not the same phenomenon

Three spatial maps may look similar but represent different processes:

• growth zoning — changes in conditions and defect incorporation during growth;
• color zoning — spatial differences in absorption that create bodycolor;
• strain pattern — optical response to stress and anomalous birefringence.

Their coincidence may be scientifically important. Their lack of coincidence is also informative.

Phosphorescence adds a time axis

Fluorescence is observed during excitation; phosphorescence after excitation ceases. If recorded spatially and over time, this produces a spatiotemporal signature of emission.

Different zones may have different phosphorescence intensities and decay rates. This can further distinguish populations and growth sectors, but decay time must always be tied to the specific measurement conditions. It is not a universal constant of a commercial diamond category.

Artifacts can imitate structure

Imaging is particularly vulnerable to image misinterpretation. The result can be affected by:

• reflections from facets;
• pavilion geometry;
• unequal distance from the source;
• shadowing by setting metal;
• excessive exposure and clipping;
• filter selection;
• surface contamination;
• digital contrast processing.

The stone is therefore rotated and viewed from multiple directions. A pattern that “moves” with a reflection is not the same as an internal growth structure.

An image is evidence only when it is traceable and auditable

Permitted image processing may include exposure correction, registration, cropping, or contrast enhancement if it does not create new information. It is impermissible to alter or generate structures so that they appear to be actual laboratory findings.

For evidentiary use, it is advisable to preserve:

• the original file;
• acquisition conditions;
• the processed version;
• a description of all transformations;
• the link between the image and the particular sample.

An AI-generated or illustratively reconstructed luminescence image has no evidentiary value for an actual stone.

[VISUAL 71.3: Facet artifact, an actual growth zone, and clipping—how to distinguish them]

When imaging concludes and when it opens the case

A clear and documented spatial pattern can strongly support an origin conclusion. If the pattern is weak, mixed, or atypical, however, the professional procedure is not to force it into a known category but to escalate:

1. repeat the image while controlling orientation and exposure;
2. compare fluorescence and phosphorescence behavior;
3. correlate with FTIR/PL data;
4. use more advanced spatial methods if necessary;
5. retain undetermined or further testing required if the evidentiary threshold has not been reached.

[VISUAL 71.4: Imaging workflow—excitation → map → artifact control → correlation → conclusion]

Chapter summary

• Luminescence imaging provides spatial information that a point spectrum alone does not.
• Excitation wavelength, filter, exposure, and orientation are part of the result.
• DiamondView is a particular deep-UV system, not a generic name for all UV imaging.
• Natural diamonds have a wide range of growth and defect patterns.
• HPHT-grown diamonds often display sectoral internal architecture.
• CVD-grown diamonds often display layering and boundaries between growth runs.
• A modern CVD diamond may deviate from the classic imaging pattern.
• Luminescence color alone does not determine origin.
• Post-growth treatment can alter emission without completely erasing growth geometry.
• Growth zoning, color zoning, and strain are not synonyms.
• Phosphorescence adds a temporal dimension to the spatial map.
• An imaging conclusion must be integrated with spectroscopy and artifact control when the pattern is ambiguous.