Two Types of Carbon Dots with Excitation-dependent Emissions and Their Application as Anti-counterfeit Ink†

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Carbon dots with excitation-dependent emission were prepared using different chlorohydrocarbon and amine as reactants under the same reaction condition. The carbon dots 1 and carbon dots 2 had selective emissions in a range of 423—556 nm and 460—555 nm,respectively,in addition,their fluorescence intensity changes could be modeled by a Gaussian-like curve with the red shift of excitation wavelengths( denoted as type Ⅰ carbon dots). The carbon dots 3 had emissions in a broad color range over the entire visible region( 407—670 nm),moreover,their fluorescence intensities had irregular change with the excitation wavelengths( denoted as type Ⅱ carbon dots). Then,fluorescence spectroscopy,transmission electron microscopy,X-ray photoelectron spectroscopy and infrared spectroscopy were explored to analyze their structural and spectral characteristics in detail. For the type Ⅱ carbon dots,except for the size effect,the surface functional groups,such as C O and C N,could efficiently introduce new energy levels for electron transitions and result in the continuously adjustable full color emissions. Further,the type Ⅱ carbon dots were demonstrated as ideal candidates for high security anti-counterfeit purpose.