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

doi:10.7503/cjcu20140559

Abstract

Abstract:

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.

Key words: Carbon dot, Fluorescence, Surface-state, Anti-counterfeiting ink

CLC Number:

TrendMD:

NIE Hui, LI Minjie, JU Bo, ZHANG Sean Xiaoan. Two Types of Carbon Dots with Excitation-dependent Emissions and Their Application as Anti-counterfeit Ink^†[J]. Chem. J. Chinese Universities, 2015, 36(2): 293.

Figures/Tables 7

Fig.1 UV-Vis absorption spectra(A) and fluorescence spectra of the C dots 1(B), C dots 2(C) and C dots 3(D) in ethanol under different excitation wavelength

Fig.2 TEM images of C dots 1(A), C dots 2(B) and C dots 3(C) Inset: HRTEM images of three C dots.

Table 1 Element contents in C dots 1, C dots 2, C dots 3 and F-C dots

Sample	Atomic ratio(%)
Sample	C	N	O	Cl
C dots 1	86.43	5.38	7.75	0.44
C dots 2	75.2	17.88	6.63	0.29
C dots 3	72.51	6.27	14.76	6.46
F-C dots	75.03	4.34	18.47	2.15

Fig.3 High-resolution XPS spectra of the C1s(A) and N1s(B) peaks for C dots 1, C dots 2, C dots 3 and F-C dots

Table 2 XPS analysis of C1s in C dots 1, C dots 2, C dots 3 and F-C dots

Sample	C—C(%)	C—N(%)	C—O(%)	C O/C N(%)
C dots 1	85.0	6.7	4.3	4.0
C dots 2	70.5	6.8	19.6	3.1
C dots 3	68.2	10.3	20.9	8.8
F-C dots	67.3	9.8	13.7	9.2

Fig.4 FTIR spectra of C dots 1(a), C dots 2(b), C dots 3(c) and F-C dots(d)

Fig.5 Photoluminescent patterns using C dots 3 solution as anti-counterfeiting inks by inkjet printing (A) Illustration of C dots 3 as ink on a ￥5 RMB practice note printed with security pattern; fluorescence microscope images of security pattern excited under UV(B), blue(C) and green(D) light, respectively.

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