Carbon Dots and Stability of Their Optical Properties

Abstract

exploited for fabrication of light-emitting devices, [5] and their remarkable electronic properties have been used in the fields of photovoltaics [6] and electronics. [5d,7] Low toxicity and the excellent biocompatibility of CDs encourage researchers to study the role of CDs in the biomedical field, and many bioimaging [8] and drug delivery [9] applications of CDs have been reported. The dependence of the optical properties of CDs on the presence of metal ions in dispersion has been exploited for cation detection applications. [10] Besides this, CDs have been demonstrated to be useful for energy storage, [11] photocatalysis, [12] electrochemical sensing, [13] electrochemiluminescence sensing, [13,14] sensing and killing microorganisms [15] including viruses, [16] and numerous other applications. Although there have been several lab-scale demonstrations of a variety of different applications of CDs, there are hardly any commercially available device based on CDs. [3] To commercialize CD-based devices/applications, stable and predictable PL emission is one of the most important requirements. In a few early studies of the properties of CDs, it was reported that the PL emission of CDs is photostable, that is, CDs are photostable. [17] Additionally, the PL quantum yield (QY) of CDs reported in early studies was very low, typically less than 10%, and emission was mostly understood to arise from the presence of surface functional groups. In recent years, due to improvements in synthesis methods and use of different raw materials, remarkable increases in the PL QY of CDs have been reported. [18] Often the bright PL emission from these CDs is comparable to that of molecular fluorophores. Molecule-like bright emission from CDs is often attributed to the presence of molecular fluorophores on the surface of CDs [19] or sometimes freely floating in dispersion due to poor purification. [20] This striking change in the optical properties gave rise to observations of other molecular features in CDs, like blinking and photobleaching.Despite hundreds of published studies exploring the synthesis, properties and application of CDs, there are relatively few reports that consider the photostability of CDs. Most reports that showed CDs to be photostable were carried out in the early years of the development of CDs, and, consequently, CDs are still considered to be photostable. However, there are also some more recent reports showing significant photobleaching of CDs. Here, we review published work on the photostability of CDs. It is noted that while there is a wide variation in the reported photostability of CDs, there is also a lack of homogeneous systematic studies. In most studies of photobleaching the geometry of the experiment (i.e., the Carbon dots (CDs) are a new class of materials which have been extensively studied due to their unique optical properties, low toxicity, and abundance of raw materials to synthesize them. In this minireview, it is highlighted that the stability of the optical properties of CDs is an important...

Yellow‐Emissive Carbon Dots with High Solid‐State Photoluminescence

“…In such CD samples, high blue emission may come from molecular fluorophores, [ 40 ] which is prone to photobleaching. [ 44 ] These features not only suggest the high fluorescence stability of Y‐CDs, but also imply the distinctive chemical structure and underlying emission mechanism of Y‐CDs differed from those of well‐known CDs with high blue emission. Therefore, the resultant Y‐CDs have a large Stokes shift, an ultra‐high PL QY, and good fluorescence stability, which is beneficial for further applications.…”

“…B‐CDs possessing similar size distribution but with lattice mismatch (Figure S5, Supporting Information) and showing more non‐polar groups (fatty linkages) on the surface (Figures S1 and S6, Supporting Information) and faster biexponential decay (Figure S4, Supporting Information) might have different underlying emission mechanism. [ 1,4,33,44 ]…”

Ultrasonic-Assisted Synthesis of N-Doped, Multicolor Carbon Dots toward Fluorescent Inks, Fluorescence Sensors, and Logic Gate Operations

“…Carbon dots (CDs) have received increasing attention owing to their excellent biocompatibility, good water solubility, low cytotoxicity, robust chemical inertness, high photo/chemical stability, and strong resistance to photobleaching [ 1 , 2 ]. They have especially demonstrated huge potential applications in a wide range of fields, such as sensing, bioimaging, drug delivery, photocatalysis, energy storage, anticounterfeiting, light-emitting diodes (LED), and so on [ 3 , 4 , 5 , 6 , 7 , 8 ].…”

Zn-assisted modification of the chemical structure of N-doped carbon dots and their enhanced quantum yield and photostability

“…CDs are known to have better photostability than molecular optical probes, but they become unstable under long-term exposure to light. [21][22][23] Continuous UV excitation leads to changes in the chemical structures within CDs, resulting in a decrease in the QY. 24 In addition, it has been reported that the photodegradation of CDs can cause cytotoxicity.…”