DiamondPlus is an advanced gemological screening instrument developed by the International Institute of Diamond Grading and Research (IIDGR), the laboratory and research division of De Beers, to detect diamonds that have been subjected to high-pressure high-temperature (HPHT) treatment or grown synthetically by HPHT processes. Employing photoluminescence (PL) spectroscopy as its primary analytical technique, the instrument identifies characteristic optical defect centres whose presence, absence, or relative intensities betray the thermal and pressure history of a stone. It operates non-destructively and at high throughput, making it well suited to the parcel-screening demands of the modern diamond trade.

The problem DiamondPlus addresses

HPHT processing poses one of the more challenging identification problems in contemporary gemmology. When applied to certain natural diamonds — most notably near-colourless or brown type IIa stones — HPHT annealing at temperatures exceeding 2,000 °C and pressures above 5 GPa can eliminate or reorganise nitrogen-related colour centres, dramatically improving apparent colour. The resulting stones may show no obvious signs of treatment under conventional gemmological examination: standard refractometry, polariscopy, and even routine spectroscopy can fail to distinguish them from untreated material. HPHT-grown synthetic diamonds present a related but distinct challenge, as they too can be produced in near-colourless form and may carry overlapping spectroscopic signatures.

Analytical principle

DiamondPlus interrogates the diamond's defect population using photoluminescence spectroscopy, a technique in which the stone is excited by a laser source and the resulting emission spectrum is recorded. Specific defect centres — most importantly the nitrogen-vacancy (NV) centre, which exists in both neutral (NV⁰) and negatively charged (NV⁻) forms, as well as the H3 centre (two nitrogen atoms flanking a vacancy) and various nickel- and silicon-related centres in synthetic material — emit at characteristic wavelengths. HPHT processing alters the relative concentrations and charge states of these centres in ways that produce diagnostic spectral signatures not present in untreated natural diamonds of equivalent type. The instrument is particularly sensitive to the NV⁻/NV⁰ ratio and to the presence or suppression of the 637 nm NV⁻ zero-phonon line, both of which shift measurably after HPHT annealing.

Workflow and output

The device is designed for rapid, semi-automated screening rather than definitive grading. A stone is placed in the instrument, the measurement is completed within seconds, and the software classifies the result into one of two categories: stones that pass without indication of HPHT processing, and stones flagged as requiring further investigation. Flagged stones are referred to a full laboratory — typically equipped with Fourier-transform infrared (FTIR) spectroscopy, UV-Vis absorption spectroscopy, and additional PL measurements at liquid-nitrogen temperatures — for a conclusive determination. DiamondPlus is therefore best understood as a triage tool within a multi-stage analytical protocol rather than a standalone grading instrument.

Role in laboratory and trade protocols

GIA and other major grading laboratories incorporate DiamondPlus, alongside instruments such as De Beers' own DiamondView and the IIDGR's AMS (Automated Melee Screening) systems, as part of layered detection workflows. The instrument is especially valuable for type IIa diamonds — stones with very low or undetectable aggregated nitrogen — which are disproportionately represented among HPHT-treated goods and which are inherently more difficult to screen by FTIR alone. Because type IIa material also includes some of the world's most celebrated colourless diamonds, accurate identification of HPHT treatment within this population carries significant commercial and ethical weight. DiamondPlus has contributed materially to the trade's ability to maintain disclosure standards as HPHT treatment became commercially widespread from the late 1990s onward.

Limitations

No single screening instrument is infallible. DiamondPlus is optimised for HPHT-related defect signatures and is not a general-purpose synthetic-diamond detector; laser-grown CVD (chemical vapour deposition) synthetics, for instance, carry different spectroscopic fingerprints and require complementary instruments. Additionally, very small melee stones may present measurement challenges, and certain natural diamonds with unusual defect populations can generate ambiguous results that necessitate full laboratory review. The instrument is accordingly positioned by IIDGR as one component of a broader analytical toolkit rather than a definitive arbiter.