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Time-resolved spectroscopy of colour centres in diamond

Wassell, Amber 2021. Time-resolved spectroscopy of colour centres in diamond. PhD Thesis, Cardiff University.
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Diamond is an extraordinary crystalline material which exhibits many extreme material properties. It is one of the hardest materials known, and it has unrivalled transparency to light across the ultraviolet, visible, infrared and THz bands. Its relatively high refractive index enhances internal reflections and gives diamond its signature sparkle. The high value of natural diamond necessitates robust investigation of a gemstone’s provenance. This was the motivation behind the research described in this thesis. Spectroscopy provides a way to characterise defects and impurities that have been incorporated into the diamond lattice, and which may reveal clues about the growth conditions. With the increased prevalence of synthetic diamond material in the gemstone market, there is a growing need for better screening. Given that it is becoming common practice for less experienced diamond appraisers to carry out this task, it is important there are simple assistive technologies which are both trustworthy and time-efficient to aid appraisers in grading. A bespoke diamond imaging rig was constructed to investigate the spectroscopic properties of suspect defects within the diamond lattice that might help differentiate between natural and synthetic gemstones. The imaging system revealed an unusual photoluminescent spectral signature with a wavelength of 499 nm. This signature had not previously been observed in natural diamond. This spectral feature became the major focus of this work. A systematic study of synthetic material of known composition led to the hypothesis that this signature is indicative of silicon incorporation during growth. Natural growth conditions preclude the incorporation of this element. A key refinement of the hypothesis was that the coexistence of nitrogen in addition to silicon was necessary for the formation of the defect associated with this spectral signature. Furthermore, the 499 nm spectral feature was only observed in samples that had been post-growth annealed in a restricted temperature window where nitrogen vacancies are known to be mobile. Based on these observations, it is proposed that the possible structure of the 499 nm colour centre is narrowed to a small family of Six Ny Vz complexes. This is an important result because the observation of this 499 nm photoluminescence feature in a gemstone of unknown provenance can potentially be used to identify whether the material is synthetic in origin.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Physics and Astronomy
Subjects: Q Science > QC Physics
Uncontrolled Keywords: Diamond, synthetic, 499 nm, luminescence, defect, colour-centre, prompt, delayed
Funders: EPSRC Centre for Doctoral Training in Diamond Science and Technology
Date of First Compliant Deposit: 26 January 2022
Last Modified: 05 Aug 2022 01:38

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