Exploring the Photoluminescence Characteristics of Nitrogen-Doped Carbon Dots

Abstract

Carbon dots, or C-Dots, are graphitic particles below 10 nm that exhibit room temperature photoluminescence (PL). The specific PL mechanism of C-Dots varies with synthesis paths and remains unresolved. This study utilizes direct current microplasmas for reliable and reproducible synthesis, exploring precursor outcomes and the discharge current's impact on surface chemistry and optical properties. The nitrogen-doped C-Dots (N-CQDs) synthesized display crystalline structures with a graphitic core, nitrogen doping, and a functionalized surface. Luminescence, originating from both core and surface states, can be finely controlled by adjusting synthesis conditions. N-CQDs, with a high photoluminescence quantum yield, hold promise for next-gen solar cell applications. The N-CQDs exhibit intriguing quantum-confined optical properties dependent on the level of nitrogen incorporation. Notably, the band energy structure of the N-CQDs is clarified, and they are integrated into a photovoltaic device as the photoactive layer, achieving an extraordinary open-circuit voltage of 1.8 V corroborating well with energy gat of CQDs and PL properties [1, 2]. We specifically highlight the use of nitrogen-doped C-Dots as an active absorbing layer in solar cells and discuss how doping can engineer their electrical, optical, and chemical properties. Nitrogen doping mainly occurs in the graphitic core as a substituted type of doping (63–67 atomic%), with enough to create emissive states without impacting the core structure. The optical and chemical properties remain stable even with re-dispersion, suggesting easy applicability for cellular imaging or optoelectronics [3]. Highly stable nitrogen-doped graphite quantum dots, prepared by atmospheric pressure microplasma, without post-synthesis treatments, yields stable, water-dispersible, and non-toxic quantum dots with a high PL quantum yield of approximately 70%.