Carbon Dots: From Intense Absorption in Visible Range to Excitation-Independent and Excitation-Dependent Photoluminescence

Abstract

Carbon dots (CDs) were hydrothermally synthesized using citric acid as carbon source and ethylenediamine as additive. The as-obtained CDs were then subjected to ultraviolet (UV) irradiation, resulting in ultraviolet-irradiated CDs (UVCDs). The morphology and size of CDs were characterized by transmission electron microscopy. Elemental analysis (EA) was employed to explore the composition of CDs. The surface functional groups of CDs were investigated with the help of Fourier transformation infrared spectroscopy. Fluorescence spectrometry and ultraviolet-visible (UV-vis) spectrophotometry were used to characterize the optical properties of CDs and UVCDs. The results show that the size of CDs was around 10 nm. C, H, O and N constituted CDs with the empirical elemental composition CH 1.26 O 0.52 N 0.22 . Apart from excitation-independent photoluminescence (PL), CDs exhibited two UV-vis absorption peaks at 340 and 451 nm. They also revealed weak near infrared (NIF) emission with excitation at 340and 360 nm. In addition to excitation-dependent PL, UVCDs showed one UV-vis absorption peak at 340 nm and extension of UV-vis absorption band to visible range, and they also displayed weak NIF emission at 340 and 360 nm excitation. Optical behaviors originated from surface defects and band bending. The as-prepared CDs could be used to harvest solar energy.

Fluorescent Nanocomposites: Hollow Silica Microspheres with Embedded Carbon Dots

“…The weak peak in the silica‐CDs spectrum at 240 nm is attributed to the π‐π* transition within the aromatic sp 2 domains of the CDs’ core [5a,28a, 33] . The other weak peak at 325 nm might be ascribed to the n‐π* transition in the surface groups, i. e. the C=O or C−O bonds of the carboxyl (‐COOH) surface groups [28b,34] . The corresponding transitions for CDs are at 235 and 335 nm, consistent with the report of Li et al [5a] .…”

Effect of nitrogen atom positioning on the trade-off between emissive and photocatalytic properties of carbon dots

“…3a ). The prominent band is found in nearly all CDs and is generally assigned to the π-π ∗ transition of the aromatic hydrocarbon domains 27 , 54 – 56 . The peak position shifts slightly from 344 to 357 nm with increasing BPEI content.…”

A Mini Review on Carbon Quantum Dots: Preparation, Properties, and Electrocatalytic Application

“…Generally, the optical absorption peaks of CQDs in the UV-visible region is usually estimated as π-π * transition of sp 2 conjugated carbon and n-π * transition of hybridization with heteroatom such as N, S, P, etc. The absorption property can be manipulated through surface passivation or modification process (Zhao et al, 2015; Jiang et al, 2016; Li et al, 2018b; Anwar et al, 2019). Jiang et al developed a facile hydrothermal method to synthesize red, green and blue luminescent CQDs by using three isomers of phenylenediamines (Jiang et al, 2015).…”