A Near-Colorless CVD Laboratory- Grown Diamond With Multiple Colors Of Fluorescence
This unusual CVD-grown diamond submitted to GSI Laboratories was noticed by researchers when the multiple colors of fluorescence were observed in the De Beers DiamondViewTM when exposed to deep SWUV. The diamond was 1.50 ct and near-colorless. The layered growth typical of CVD diamonds is also observable in the growth patterning. Image @ Maria Mrozek, GG
Recently the Gemological Science International (GSI) laboratory in New York observed, for the first time, a near-colorless laboratory-grown CVD diamond with just over 1.50 carats with unusual fluorescent coloration. While being exposed to short wave ultraviolet radiation (225 nm) in the DiamondView imaging instrument, it was seen exhibiting all the colors of the rainbow at the same time!
CVD laboratory-grown diamonds only began to emerge commercially in the jewelry market after 2008. Therefore, they are still relatively new material, and their growth processes and post-growth treatments are continuously evolving. This creates opportunities to observe unusual diamonds, such as this one, that have not yet been reported.
One way of differentiating natural from laboratory-grown diamonds includes the visual observation of polished diamonds utilizing specialized types of imaging such as the images generated in an instrument known as the De Beers DiamondViewTM instrument. The diamond is placed in a diamond in an enclosed chamber while it is exposed to high energy UV rays. The resulting reaction is seen live on a computer monitor. One of the reactions seen is a form of luminescence called fluorescence.
Typically, the fluorescence seen in laboratory-grown CVD diamonds consists of one color with the possibility of an additional modifying color or two. The coloration of the fluorescence, phosphorescence, along with the structural growth patterns seen helps to separate natural from laboratory-grown CVD diamonds.
Fluorescence is a form of luminescence, which is a general term to describe the process in which a material (in this case, diamond) absorbs a “cool” (an energy other than heat, in this case light) from an external source (the sun or a UV lamp) and re-emits that energy in the form of visible light that makes the diamond glow.
Luminescence is sub-categorized by what energy source is applied, or how the material reacts after the energy is applied. It is encountered in everyday life more often than is recognized. Types of luminescence can include chemiluminescence (the emission of light resulting from a chemical reaction, such as glow sticks at a party), electroluminescence (the result of an electric current such as the backlight on an LCD display of a watch), and in the case of diamonds, photoluminescence.
Diamonds exhibit photoluminescence which is an emission of light as a result of photons (electromagnetic radiation such as radio waves, microwaves, infrared, light, ultraviolet, X-rays, and gamma rays) being applied to the material.
Photoluminescence is then subdivided as fluorescence, or phosphorescence according to how the material (diamond) reacts. Fluorescence is the glow that occurs while the energy source is applied and may only last a few nanoseconds (undetectable by the human eye) after the energy source is shut off. Another familiar but rare luminescence diamond displays is phosphorescence, which is the glow that is observed after the energy source is shut off. Phosphorescence and may last from milliseconds (detectable by the human eye from about 80 milliseconds) to a few hours in rare cases.
How Fluorescence Works
How Phosphorescence Works
The different coloration given off by fluorescence is the result of the different “recipes” that have been used during the growth process. Also influencing this are the additional treatments of annealing and pressure that may be used to improve this diamond’s near-colorless body color as seen in daylight or its equivalent.
Trace amounts of impurity elements incorporated during growth such as nitrogen, boron, or silicon can contribute to the formation of luminescence centers. Most optically active defects in diamond usually consist of the impurity atom bound to structural defects such as vacancies or interstitial carbon. Nitrogen-based defects produce the broadest array of luminescent centers that extend through the entire visible spectrum as well as into the near infrared (NIR).
Typical luminescence centers for CVD-grown diamonds include the NV0 and NV- which cause an orangy fluorescence, the N3 center which contributes a blue color, and SiV centers which can emit in the red and NIR. There are numerous other defect and vacancy-related centers that can contribute to the observed reaction to this diamond in SWUV, but these may be the most likely.
This unusual CVD-grown diamond submitted to GSI Laboratories was noticed by researchers when the multiple colors of fluorescence were observed in the De Beers DiamondViewTM when exposed to deep SWUV. The diamond was 1.50 ct and near-colorless. The layered growth typical of CVD diamonds is also observable in the growth patterning. Image @ Maria Mrozek, GG
Fluorescence of Natural and Synthetic Gem Diamond: Mechanism and Applications Christopher M. Breeding Sally Eaton‐Magaña. Image @ Maria Mrozek, GG
Based on the DiamondViewTM image, the theory is that this diamond underwent multiple changes in growth chemistry and conditions as it was crystallizing and likely underwent a form of post-growth treatment possibly including high-pressure heating. This would explain the presence of N3, NV, and Si centers. Studies have shown changes in fluorescence colors (from red through green to turquoise) depending on the annealing temperature of post-growth treated CVD diamond samples that had high concentrations of silicon and nitrogen which would support the theory that this diamond has been subject to post-growth treatment.
Additional analysis would be required to determine the relative peaks and intensities of each of the luminescence centers observed in this diamond in order to identify them and make a definitive conclusion about their growth and treatment process.
CVD laboratory-grown diamonds are grown by a number of manufacturers that specialize in this field. Even though the processes and growing “recipes” resulting in laboratory grown diamonds have undergone numerous investigational analysis and reporting from the scientific community there is always something new and unusual to be discovered and shared.