Sally Eaton-Magaña

Using phosphorescence as a fingerprint for the Hope and other blue diamonds

Sixty-seven natural blue diamonds, including the two largest such gemstones known (the Hope and the Blue Heart), were probed by ultraviolet radiation, and their luminescence was analyzed using a novel spectrometer system. Prior to this study, the fiery red phosphorescence of the Hope Diamond was regarded as quite rare compared to greenish-blue phosphorescence. However, our results demonstrated that virtually all blue diamonds phosphoresce at 660 nm (orange-red) but that this emission often is obscured by a concomitant luminescence at 500 nm (green-blue). Although both bands were nearly always present, the relative intensities of these emissions and their decay kinetics varied dramatically. Consequently, phosphorescence analysis provides a method to discriminate among individual blue diamonds. Treated and synthetic blue diamonds showed behavior distinct from natural stones. Temperature-dependent phosphorescence revealed that the 660 nm emission has an activation energy of 0.4 eV, close to the 0.37 eV acceptor energy for boron, suggesting that the phosphorescence is caused by donor-acceptor pair recombination.

Pink-to-Red Coral: A Guide to Determining Origin of Color

pale-colored and white coral into the more highly valued shades of pink to red. Commonly, the coral is bleached prior to the dyeing process so that better penetration and more homogeneous coloration may be achieved (figure 3). Additionally, polymer impregnation—with or without a coloring agent— may be used to enhance the appearance of coral and give it a smoother surface, which makes it more comfortable to wear (see, e.g., Pederson, 2004). The present article looks at the current status of this ornamental material—its formation, supply, and the potential impact of environmental considerations—as well as the techniques used to distinguish between natural-color and dyed corals. In particular, this article will outline some of the procedures typically used by gemologists and gemological laboratories to determine the origin of color for pink-to-red coral. PINK-TO-RED CORAL: A GUIDE TO DETERMINING ORIGIN OF COLOR

Fluorescence Spectra of Colored Diamonds Using A Rapid, Mobile Spectrometer

have been chronicled in natural diamonds using UVVis absorption, cathodoluminescence, and photoluminescence spectroscopy (see, e.g., Zaitsev, 2001), spectral data for fluorescence and phosphorescence are limited in the gemological literature, since luminescence is typically described by visual observations (again, see Fritsch and Waychunas, 1994). However, visual assessment of fluorescence and phosphorescence tells only part of the story. The color discerned by the unaided eye may represent a combination of two or more wavelength regions. For example, Anderson (1960) asserted that although most fluorescing diamonds appear to luminesce blue, a yellow or green component may be present but masked by the stronger blue emission. He used color filters and a spectroscope to try to identify some of the relevant FLUORESCENCE SPECTRA OF COLORED DIAMONDS USING A RAPID, MOBILE SPECTROMETER

Strongly Colored Pink CVD Lab-Grown Diamonds

modifying the occurrence or arrangements of particular lattice defects, either during growth or with post-growth treatments. In this study, we describe a group of strongly colored pink CVD lab-grown diamonds (e.g., figure 1) provided for examination by Apollo Diamond Inc. Standard gemological properties and spectroscopic data are presented, as well as key identification features that help separate these new products from natural, treated-natural, and HPHT-grown synthetic pink diamonds.

Developments in Gemstone Analysis Techniques and Instrumentation During the 2000s

The first decade of the 2000s continued the trend of using more powerful analytical instruments nto solve gem identification problems. Advances in gem treatment and synthesis technology, and nthe discovery of new gem sources, led to urgent needs in gem identification. These, in turn, led to nthe adaptation of newer scientific instruments to gemology. The past decade witnessed the nwidespread use of chemical microanalysis techniques such as LA-ICP-MS and LIBS, luminescence nspectroscopy (particularly photoluminescence), real-time fluorescence and X-ray imaging, nand portable spectrometers, as well as the introduction of nanoscale analysis. Innovations in laser nmapping and computer modeling of diamond rough and faceted stone appearance changed the nway gemstones are cut and the manner in which they are graded by gem laboratories.

An Introduction to Photoluminescence Spectroscopy for Diamond and Its Applications in Gemology

Photoluminescence (PL) spectroscopy is frequently mentioned in the gemological literature, but its relevance to the wider trade audience is rarely discussed. Due to the possibility of an undisclosed treatment or a synthetic origin, all type II diamonds (both colorless and fancy-color) and colorless type IaB diamonds submitted to gemological laboratories should ideally be tested using PL spectroscopy. Although the proportion of samples that require this testing is small, the failure to properly identify treated and synthetic diamonds could destabilize the diamond industry. This article seeks to clarify the underlying physics and methodology of this important tool for gemologists.

Characterization of Colorless Coated Cubic Zirconia (Diamantine)

GEMS & GEMOLOGY SPRING 2012 Sophisticated techniques used in the semiconductor and optical coating industries are now being applied to the treatment of gemstones. In the past few years, the jewelry industry has witnessed the introduction of several faceted gem materials (diamond, topaz, quartz, cubic zirconia, and others) reportedly coated with thin colored or colorless surface layer(s) of substances such as aluminum oxide, diamond-like carbon (DLC), and nanocrystalline synthetic diamond to change their color or allegedly improve their appearance and/or durability (see, e.g., Henn, 2003; Shen et al., 2007; Ogden, 2008; Schmetzer, 2008; Bennet and Kearnes, 2009). These new coating treatments present several important challenges for the jewelry trade, including their proper description, identification, determination of any visual or physical effects resulting from the coating, and disclosure (see box A). For the past several years, Serenity Technologies of Temecula, California, has produced and marketed a simulant consisting of faceted cubic zirconia (CZ) coated with what is described as a thin, transparent, colorless layer containing submicroscopic particles of nanocrystalline synthetic diamond embedded in a matrix material (see figure 1 and www.serenitytechnology.com). This product is currently sold under the brand name Diaman tine and is distributed only through licensed dealers. The Diamantine production process has a capacity of 2,000 carats in each cycle, for a total of 20,000 carats per day (S. Neogi, pers. comm., 2009). Colorless and variously colored thin-film layers can be deposited on CZ by this process. With modifications to the surface-cleaning procedure, similar layers can also be deposited on other gem materials, including emerald, opal, and tanzanite. Colored gemstones coated with diamond-like carbon have been available in the trade for years (Koivula and Kammerling, 1991). CHARACTERIZATION OF COLORLESS COATED CUBIC ZIRCONIA (DIAMANTINE)

Recent Advances in CVD Synthetic Diamond Quality

1952 by William Eversole of the Union Carbide Corporation, but it took another two decades before GIA issued the first grading report for a laboratorymade diamond (Crowningshield, 1971). Virtually all single-crystal synthetic diamonds are made by two very different processes. High-pressure, high-temperature (HPHT) synthesis mimics some of the key conditions for natural diamond formation, with pressures of 5–6 GPa and temperatures of 1400– 1600oC applied to a carbonaceous source material. The second method, chemical vapor deposition (CVD), involves growing synthetic diamond as thinfilm layers at moderate temperatures and low (i.e., below atmospheric) pressures. One of the main advantages of the CVD procedure over HPHT is the superior flexibility of synthetic diamond size and geometry produced. Furthermore, intentional doping with impurity elements can be controlled by the addition of gases containing those atoms. Diamond, with its superlative physical properties, is of great interest for both scientific and technological reasons. CVD synthesis uses technology similar to that employed for producing silicon-based computer chips and electronics. In fact, many of the technological improvements in synthetic diamond quality are fueled by industrial applications, with commercial gem production a largely ancillary concern (Balmer et al., 2009). Most current research efforts are focused on maximizing growth control and rates, improving purity, and understanding defect incorporation (e.g., Silva et al., 2008; Butler et al., 2009). The processes occurring in the gas phase and on the surface are complex and acutely sensitive to even minute changes to various parameters, such as surface orientation and smoothness, hydrocarbon-to-hydrogen ratio, substrate temperature, plasma density, and impurities present (e.g., Martineau et al., 2004; Silva et al., 2008). As a result of this research effort, the quality of CVD products has advanced greatly over the last decade. Gem-quality CVD synthetic diamond (e.g., figures 1 and 2), once considered a “holy grail,” is now routinely produced thanks to several technical and experimental improvements.