Spectroscopic Characteristics of Treated-Color Natural Diamonds

Abstract

With the increasing availability of treated-color diamonds on the market, their characterization is becoming more and more critical to the jewelry testers and customers. In this investigation, ten color diamonds treated by irradiation (4 pieces), HPHT (3 pieces), and multiprocess (3 pieces) were examined by spectroscopic methods. These diamonds are classified to be type Ia according to their FTIR characteristics. Using microscope and DiamondView, the internal features (such as distinctive color zoning and graphitized inclusions) and complex natural growth structures were observed, which show that the samples are more likely artificially colored natural diamonds. Through photoluminescence spectroscopy, a combination of optical centers was detected, including N-V 0 at 575 nm, N-V − at 637 nm, H3 at 503 nm, H2 at 986 nm, and GR1 at 741 and 744 nm. Combining with the previous studies, treatment conditions for the studied diamonds were estimated depending on the presence and/or absence of the optical centers. In addition, the coloration mechanism of the samples (blue, green, and red) during the treatment process was also discussed. It is suggested that a number of techniques should be combined in order to make a reliable identification for such diamonds.

Hydrogen-Rich Green Diamond Color-Treated by Multi-Step Processing

“…A ZPL at 613 nm center with its vibrational feature at 625 nm (a weak hillock in spectrum shown in figure 5A) is also a common feature of purple diamonds (Titkov et al, 2008). The 647 nm center has been reported in irradiation-treated diamonds (Wang et al, 2018) and is believed to be an irradiation-related defect (Zaitsev et al, 2018). Photoluminescence spectra taken with 532 nm laser excitation revealed pronounced emissions of NV 0 and NVcenters.…”

“…In the laboratory, attempts have been made to artificially induce green color in diamonds. This can be done with high-energy electron irradiation of yellowish diamonds (Collins, 1982;Wang et al, 2018), followed by prolonged annealing at a temperature of 1400°C for colorless type Ia diamonds (Collins, 2001), or using high-pressure, hightemperature (HPHT) annealing for brown type Ia diamonds (Collins et al, 2000;Collins, 2001Collins, , 2003. A multi-step processing that probably involved irra-diation, annealing, and re-irradiation was documented by GIA researchers (Fritsch et al, 1988).…”

Nitrogen Structure Determination in Treated Fancy Diamonds via EPR Spectroscopy

“…Blue and green diamonds display visible spectra with a large band between 400 and ~600 nm, which may be associated with the H3 defect (N-V-N defect) [2]. The GR1 center is attributed to the neutral isolated vacancy (V • ) located at 741 and 744 nm, which is seen in both green and blue diamonds [34].…”

The effects of thermal treatment and irradiation on the chemical properties of natural diamonds

“…Such thermal treatment involved controlled heating and cooling. [18][19][20] Heating in the 400-1300 1C temperature range in the absence of molecular oxygen (to avoid oxidation of the diamond to carbon dioxide) is conducted until the desired color is achieved. This process eliminates undesirable color centers and improve diamond color quality.…”