The effects of defect states on the fluorescence (FL) and electrochemiluminescence (ECL) properties of graphite phase carbon nitride (g-CN) are systematically investigated for the first time. The g-CN nanosheets (CNNSs) obtained at different condensation temperatures are used as the study models. It can be found that all the CNNSs have two kinds of defect states, one is originated from the edge of CNNSs (labeled as CN-defect) and the other is attributed to the partially carbonization regions (labeled as C-defect). Both two kinds of defect states substantially affect the luminescent properties of CNNSs. Both the FL and ECL signals of CNNSs contain a band gap emission and two defect emissions. For the FL of CNNSs, decreasing the density of defect states can increase efficiently the FL quantum yield, while increasing the density of defect states can make the FL spectra red shift. For the ECL of CNNSs, increasing the density of CN-defect states and decreasing the density of C-defect states are greatly important to improve the ECL activity. This work provides a deep insight into the FL and ECL mechanisms of g-CN, and is of significance in tuning the FL and ECL properties of g-CN. Also, it will greatly promote the applications of CNNSs based on the FL and ECL properties.

Surface-enhanced Raman Scattering (SERS) is a sensitive and nondestructive technique that provides fingerprint structural information of molecules. Designing and constructing sensitive and stable SERS substrates is of great significance for the application of the technique. In this study, single-layer carbon-based dots (CDs) are used as capping agents to synthesize gold nanoparticles (AuNPs/CDs) and manganese dioxide nanosheets (MnO2/CDs), which are then hybridized through a simple cocentrifugation method. After the hybridization, the monodispersive AuNPs/CDs aggregate obviously into some clusters exhibiting strong SERS activity due to the electromagnetic “hot spots” effect, and the MnO2/CDs also show outstanding SERS activity due to the charge-transfer resonance effect. The obtained nanohybrids (MnO2/CDs/AuNPs) with robust chemical stability combine well with the electromagnetic enhancement of AuNPs/CDs and chemical enhancement of MnO2/CDs, leading to an ultrahigh enhancement factor of 3.9 × 108. Based on the novel SERS substrate, a sensitive and rapid sensing system for the detection of malachite green is developed, with a low detection limit of 1 × 10–9 M. This work provides a valuable model for designing and fabricating high-performance SERS substrates.

throughput, and rapid response, SERS has great potential in applications including surface science, [2,3] material science, [4] biological medicine, [5] drug analysis, [6] food safety, [7,8] environmental testing, [9] and so on. It is well known that SERS tests require the target molecules to be adsorbed on the surface of certain special materials (so-called SERS substrate), and the SERS response is greatly dependent on the nature of the substrate. The present SERS substrates usually suffer from the major disadvantages of low sensitivity, poor stability, poor uniformity, and weak anti-interference ability. [10,11] Electromagnetic enhancement (EM) and chemical enhancement (CM) are two widely accepted processes involved in the SERS mechanism. Usually, EM is considered to play a greater role than CM. [12,13] Accordingly, many SERS substrates have been designed based on the strong localized surface plasmon resonance (LSPR) of noble metals. [14] In particular, various silver (Ag) based nanostructures have been developed for SERS substrate due to their strong LSPR. [15,16] However, the constructed Ag based SERS substrates tend to be only responsive to certain specific molecules but are insensitive to many important molecules to be tested. [17] Thus, improving the SERS activity of Ag-based substrates is still greatly necessary. The contribution of CM in Ag-based substrates is usually covered up by the CM, and is usually ignored. Recently, increasing research results suggest a non-negligible role of CM in SERS. [18] In particular, many semiconductor-based nanomaterials have been found to have high enhancement factors (EFs) up to 10 5 -10 6 relying only on the CM. Can Ag based substrates also have such a strong CM? If yes, how to coordinate efficiently the CM and EM to gain the strongest SERS activity? To gain the maximum CM effect, a laser with matched energy should be applied according to the energy level of the target molecule and the Fermi level of Ag to ensure the efficiency of charge transfer (CT). [19] Thus, lasers of different wavelengths may be selected for different target molecules. At the same time, to achieve an optimal EM effect, Hydrogel surface-enhanced Raman scattering (SERS) chips with tunable localized surface plasmon resonance (LSPR) wavelength are prepared to coordinate the chemical enhancement (CM) and electromagnetic enhancement (EM) effects for molecules. When detecting different molecules, a laser with matched energy is selected according to energy intervals between the molecular energy levels and the Fermi level of Ag nanoparticles to obtain the strongest CM effect. Meanwhile, a hydrogel SERS chip with the LSPR wavelength matching with the laser is selected to gain the strongest EM effect. As a result, the constructed hydrogel SERS chips show outstanding activity to many molecules. Amoxicillin, pymetrozine, and chlorpyrifos are used as the model molecules to demonstrate the great importance of CM effect and the working principle of the obtained hydrogel SERS chips. Besides the ultrahigh activity,...

Carbon based dots nanoclusters (CDCs) are reported for the first time. The morphologies of the obtained CDCs are characterized by transmission electron microscopy and atomic force microscopy. It is found...

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