Influence of ion implantation on the fluorescence quantum yield of diamond

Fluorescent markers became powerful tools in the field of bioimaging and biosensing. Thanks to their fast response, high specificity and sensitivity, tracking of biomolecules/organelles in biological processes became possible. Surface functionalisation can be used to apply them in biomedical applications such as diagnostic probes or therapeutics. However, fluorescent markers still face certain challenges such as photobleaching, blinking and toxicity. This is where fluorescence nanodiamonds (FNDs)  come into play with their highly stable optical and chemical properties and lack of toxicity. Their surface can also be functionalised to target specific biomolecules and/or cells. FNDs can be produced using a variety of methods with a wide range of sizes ranging from several nm to tens of μm, which defines their penetration and adhesion properties. In contrast, nanoparticles which utilise plasmon resonance effects, such as gold nanoparticles, can’t have this size flexibility due to their emission nature. FNDs are also currently available in commercial volumes and their production can be scaled up on demand.

Nonetheless, to date there has been low usage of FNDs as a biomarker due to their weak quantum efficiency compared to all other biomarkers, nanoparticle and fluorescent dyes. Thus, the main challenge is to enhance emission intensity from the FNDs. Radiative recombination in diamond is defined not by carbon band-to-band transitions, but by transitions from the sub-band states. These sub-band states are created by impurity atoms in the diamond structure. For this reason, it is possible to obtain optical emission from diamond by incorporating additional elements into the lattice by ion implantation.


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