Temperature dependence time-resolved luminescence spectroscopy in synthetic NV0 centers Ffion James 1 , Amber Wassell 1 , Colin McGuinness 2 , Georgina M. Klemencic 1 , Chris Hodges 1 , Stephen A. Lynch 1 1 School of Physics and Astronomy, Cardiff University, UK, 2 De Beers Group Ignite, UK Recent improvements in synthetic diamond fabrication have resulted in challenges when differentiating between natural and artificial stones using traditional techniques, 1 for example temperature dependent optical spectroscopy or gemmological identification. While these techniques can currently identify synthetic stones via their chemical composition, anomalous birefringence, and red-shifted emissions, 2,3 future stones may need additional characterisation techniques. As the quality of synthetic stones increases, the ability to correctly separate them from natural diamond becomes an ever more challenging, yet vital, task since a diamond’s origin affects its properties and value in both a scientific and industrial capacity. Here we present temperature-dependent optical spectroscopy of a synthetic CVD single-crystal diamond to investigate both the electronic structure and optical characteristics. Time resolved prompt and delayed luminescence measurements, focusing on the NV 0 defect, were conducted using an above-bandgap (190 - 227 nm) spectrally-filtered microsecond xenon flash lamp from 77 - 350 K. On prompt luminescence timescales (µs) we find that NV 0 ’s zero phonon line (ZPL, 575 nm) is unaffected by temperature. We find that while this peak is also seen in delayed luminescence, it gradually disappears below 190 K with a concurrent gradual appearance of a broadband centred around 460 nm. The observed temperature- dependence of the ZPL is further supported by imaging on the same prompt and delayed luminescence timescales. When imaging delayed luminescence emission, a colour change is observed from orange to blue as the NV 0 centre disappears and is replaced by the broad peak dominating the spectrum centred around 460 nm. Both the delayed luminescence spectra and the imaging show the return of the NV 0 defect as the temperature is raised to 290 K. Within the broadband peak, three distinct peaks of unknown origin emerge in the delayed luminescence spectra as the temperature is reduced. At low temperatures, following the disappearance of the NV 0 ZPL, we consider the unknown defect to be of a higher concentration due to the greater peak intensity. Further investigation of these defects may provide alternative means of identifying synthetic diamonds which will benefit both scientific and industrial communities. References
1. Lu, T. et al . Journal of Gemmology 36 , 748–757 (2019). 2. Peng, D., Liu, Y. & Zhao, Phys.: Condens. Matter 4 , (1992). 3. Eaton-Magaña, S. & Shigley, Gems & Gemology 52 , (2016).
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