Near-Ultraviolet to Near-Infrared Fluorescent Nitrogen-Doped Carbon Dots with Two-Photon and Piezochromic Luminescence

Abstract

Carbon dots (CDs) have gained intensive interests owing to their unique structure and excellent optoelectronic performances. However, to acquire CDs with a broadband emission spectrum still remains an issue. In this work, nitrogen-doped CDs (N-CDs) with near-ultraviolet (NUV), visible, and near-infrared (NIR) emission were synthesized via one-pot solvothermal strategy, and the excitation-independent NUV and NIR emission and excitation-dependent visible emission were observed in the photoluminescence (PL) spectra of N-CDs. Moreover, the as-synthesized N-CDs displayed two-photon fluorescence emission. It is important to note that N-CDs also exhibited piezochromic luminescence with reversibility, in which the red- and blue-shifted PL with increasing applied pressure (0.07-5.18 GPa) and the red- and blue-shifted PL with releasing applied pressure (5.18 GPa to 1 atm) were developed for the first time. Combined with good hydrophilicity, high photobleaching resistance, and low toxicity, the piezochromic luminescence would greatly boost the valuable applications of N-CDs.

Recent advance of carbon dots in bio-related applications

“…Further advancement is needed to improve the PL QY for high intensity or contrast image. Recently, several groups have been reported highly fluorescent red-emissive CDs with PL QY as high as 86% [16] and the emission peak was also extended NIR region (725 nm) [17]. This progress shined light of the further application of CDs in the bio-related applications [18].…”

“…The two-photon emission provides another potential route to overcome the low tissue penetration depth of the short-wavelength light source. NIR light has large penetration depth, which can be used as the excitation light and generate fluorescence in the visible light region for easy observation [17,20,21]. Furthermore, room temperature phosphorescence (RTP) properties of CDs were observed in the various organic, polymer or inorganic matrixes.…”

Near-infrared emissive carbon dots with 33.96% emission in aqueous solution for cellular sensing and light-emitting diodes

“…Red fluorescence emitting materials are favorable for many applications, particularly in the biomedical fields, because blue light and ultraviolet light usually cause damage to biological tissues [22,23]. Since the discovery of CDs, researchers have explored a variety of synthesis pathways to prepare CDs from a variety of carbon sources, such as arc discharge, laser ablation [24,25], electrochemical synthesis [26,27], microwave [28,29], acidic oxidation, solvothermal methods [30,31], and hydrothermal methods [32][33][34][35]. Among these, hydrothermal and solvothermal methods are environmentally friendly and economical synthesis methods because the as-prepared CDs do not require further passivation.…”

Photocatalytic Degradation of Organic Dyes and Antimicrobial Activities by Polyaniline–Nitrogen-Doped Carbon Dot Nanocomposite

“…The bands at 1583 and 1586 cm −1 are denoted as the –N–H asymmetrical stretching vibration and the C=C stretching vibration is evinced by the 1506 cm −1 peak [ 39 ]. The bands at 2156 and 2953 cm −1 indicate the aromatic C=C stretching vibration and C–H aliphatic and aromatic stretching vibration [ 41 ]. The peaks at 1088 and 1100 cm −1 are due to the C–O stretching vibration and =C–H in-plane vibration [ 42 ].…”