Abstract
Representing single-layer to tens of layers of graphene in a size less than 30 nm, carbon quantum dots (CQDs) is becoming an advanced multifunctional material for its unique optical, electronic, spin and photoelectric properties induced by the quantum confinement effect and edge effect. In present work, upon co-doping engineering, nitrogen and chlorine co-doped CQDs with uniquely strong blue-green double emissions are developed via a facile and one-pot hydrothermal method. The crystalline and optical properties of CQDs have been well manipulated by tuning the mole ratio of nitrogen/chlorine and the reaction time. The characteristic green emission centered at 512 nm has been verified, originating from the chlorine-related states, the other blue emissions centered at 460 nm are attributed to the conjugated π-domain. Increasing the proportion of 1,2,4-benzentriamine dihydrochloride can effectively adjust the bandgap of CQDs, mainly caused by the synergy and competition of chlorine-related states and the conjugated π-domain. Prolonging the reaction time promotes more nitrogen and chlorine dopants incorporate into CQDs, which inhibits the growth of CQDs to reduce the average size of CQDs down to 1.5 nm, so that the quantum confinement effect dominates into play. This work not only provides a candidate with excellent optical properties for heteroatoms-doped carbon materials but also benefits to stimulate the intensive studies for co-doped carbon with chlorine as one of new dopants paradigm.
Highlights
Nanocrystals have received both fundamental and practical attention owing to their potential applications in many fields such as ultrasensitive biosensing, imaging agents, photothermal therapy and catalysts, due to their tunable optical properties and high catalytic activities [1,2,3,4,5,6,7,8,9]
Yang et al demonstrate that N and Se doping can achieve a tunable emission wavelength in Carbon quantum dots (CQDs) and the fluorescence is close to the surface activity groups [21]; Qu et al prepared S, N co-doped CQDs with multicolor emissions and found that the luminescence may come from the carbon core [18]
The emission origination of CQDs can be divided into two categories: one is intrinsic state related to conjugated π-domains in CQDs [22,23], the other is surface/defect/edge state related to the surface groups or defects [24,25,26,27]
Summary
Nanocrystals have received both fundamental and practical attention owing to their potential applications in many fields such as ultrasensitive biosensing, imaging agents, photothermal therapy and catalysts, due to their tunable optical properties and high catalytic activities [1,2,3,4,5,6,7,8,9]. The existence of C–Cl and C–N bond and its corresponding concentration in CQDs exhibited great influence on the degree of carbonization of CQDs, implying that the introduction of nitrogen and chlorine might significantly affect the luminescent properties of CQDs. In order to clarify the influence mechanism of reactants ratio on the optical properties of N, Cl co-doped CQDs, their absorption and photoluminescence properties have been studied in detail.
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