Laboratory-created diamonds now on the market are grown under high-pressure, high-temperature (HPHT) conditions, and in the last few years, they have become more available in the jewelry trade. EGL USA has studied yellow-to-orange synthetic diamonds from Chatham Created Gems and the Gemesis Corporation (Woodring and Deljanin, 2004), and as a result of this research is offering a laboratory service of testing and certifying synthetic diamonds. This is the first study of synthetic diamonds created by Advanced Optical Technologies Corp. (AOTC), based in Ottawa, Canada. They are producing as-grown yellow-to-orange, blue, and near-colorless synthetic diamonds, as well as pink-to-purple ones that are produced by the irradiation and annealing of as-grown yellows. Produced in Europe using Russian BARS-type presses, the crystals typically weigh 1-4 ct, and the polished samples are 0.50-2 ct. Recently AOTC has started commercially selling their synthetic diamonds for jewelry purposes in North America under the name "Adia Created Diamonds." All of the faceted stones are certified and laser inscribed as "AOTC-created" at EGL in Vancouver, Canada. Since the color of AOTC-created diamonds is stable, EGL is grading them with the same terminology that is used for natural diamonds. We examined the following AOTC synthetic diamonds: 247 yellow to orange (Fancy Light to Fancy Vivid), 68 blue (light to Fancy Vivid), eight pink to purple (Fancy Intense to Fancy Deep), and five near colorless (D to I). Some contained gray metallic inclusions that were irregular in shape and very different from crystals seen in natural diamonds. Their clarity grades ranged from VVS to I, with the majority (59%) in the VVS to VS categories. Most synthetic diamonds from other producers can be identified by a characteristic cross-shaped UV luminescence pattern that is stronger in short-wave than in long-wave UV radiation. The majority of the AOTC-created diamonds did not show characteristic color zoning nor any fluorescence pattern when illuminated with a standard UV lamp, so we used UV sources with higher intensity such as the DiamondView and a custom-made EGL instrument (at wavelengths of 220, 254, and 365 nm). With this UV illumination, we could observe the cubo-octahedral color zoning that is typical of HPHT-grown synthetic diamonds. These new AOTC-created synthetic diamonds can be separated from their natural counterparts based on careful observation with the microscope, and through the use of crossed polarizers, the DiamondView, and advanced spectroscopy. [ABSTRACT FROM AUTHOR]