Highly fluorescent nitrogen-doped carbon dots with excellent thermal and photo stability applied as invisible ink for loading important information and anti-counterfeiting

Abstract

High quantum yields (QY) and stable performances are prerequisites for implementing carbon dots in practical applications. In this study, we demonstrate that nitrogen-doped carbon dots (N-CDs), which were prepared via the hydrothermal treatment of citric acid (CA) and tris(hydroxymethyl)methyl aminomethane (Tris), have a high QY of 75%, together with excellent thermal and photo stability. These N-CDs deliver an excellent thermal stability performance over the temperature range of 25 °C to 95 °C, and even at a heating temperature of 90 °C for 360 min. Upon exposure to UV illumination with a radiant intensity of 20 mW cm, 96% fluorescence intensity is retained. This florescence stability performance is probably due to the chemical composition and steric effect of the nitrogen-doping agent. Furthermore, the remarkable optical properties of these N-CDs allow them to be used as invisible ink for loading important information and advanced anti-counterfeiting.

High-Efficient Excitation-Independent Blue Luminescent Carbon Dots

“…The high-resolution spectrum of N1s suggested the presence of pyrrolic-like N (399.7 eV) and graphitic-like/amino N (400.7 eV). The two peaks of O 1s high-resolution spectrum at 531.55 and 532.31 eV are attributed to C=O and C–OH/C–O–C bonds [21–24]. The results of XPS analysis is in good agreement with the FTIR spectrum.…”

“…Discernible lattice structures of CDs in the TEM images indicate that the resultant nanoparticles have the inner cores of graphite. The XRD diffraction pattern of the CDs shows a wide peak at 20.24° (Additional file 1: Figure S1), close to the (002) interlayer spacing of a graphitic structure [5, 21]. The G band at 1598 cm −1 and D band at 1350 cm −1 of CDs were not obvious on the Raman spectra (Additional file 1: Figure S2).…”

“…The Raman characterization might be disturbed by the strong fluorescence of CDs. Also, the absence of the two peaks further proves that the CDs are composed of nanocrystalline graphite-like core and disordered sp 3 -carbon [21].

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Multilevel Data Encryption Using Thermal‐Treatment Controlled Room Temperature Phosphorescence of Carbon Dot/Polyvinylalcohol Composites

“…Carbon dots (CDs) satisfy the requirements of low toxicity,11 biocompatibility,12 high photostability,13 and low cost,14 and offer versatile luminescent properties suitable for a variety of applications 15, 16, 17, 18, 19, 20, 21, 22. Phosphorescence from CDs in PVA matrix was firstly reported by Zhao's group in 2013 23.…”

pH‐sensitive carbon quantum dots−doxorubicin nanoparticles for tumor cellular targeted drug delivery

“…Figure S1 is an X‐ray diffraction pattern (XRD) of the prepared N‐CQDs. It is shown from the figure that N‐CQDs exhibit broad diffraction peaks around 2 ɵ = 24 o , which is consistent with the (002) crystal plane in the graphite structure, indicating the amorphous characteristics of the sample. The reason for the analysis of this phenomenon may be that the reaction is so fast that lead to incomplete product lattice structure, which makes the surface of N‐CQDs more defective, and its surface contains a large number of functional groups such as amino group, carboxyl group, and hydroxyl group.…”