Carbon dots (CDs), as emerging luminescent nanomaterials, possess excellent but complex properties, bringing about extensive attention and a lot of controversy. In this Perspective, we put forward the concept of “carbonized polymer dots” and emphasize the important role of polymerization and carbonization during the formation of CDs. We explore the common characters and clarify the complicated relationship of CDs, based on the reasonable classification of graphene quantum dots, carbon quantum dots, and carbonized polymer dots. Moreover, different perspectives are provided for comprehensive analysis about the essence of CDs, including quantum dots, molecules, and polymers. The photoluminescence mechanism has been classified into molecule state, carbon core state, surface/edge state, and cross-link enhanced emission effect for further understanding of complicated phenomena.

The crosslink‐enhanced emission effect was first proposed to explore the strong luminescence of nonconjugated polymer dots possessing only either non‐emissive or weakly emissive sub‐luminophores. Interesting phenomena in recent research indicate such enhancement caused by extensive crosslinking appears in diverse luminescent polymers with sub‐luminophores (electron‐rich heteroatomic moieties) or luminophores (conjugated π domains). This enhancement can promote the emission from nonluminous to luminous, from weakly luminous to strongly luminous, and even convert the pathway of radiative transitions. The concept of the crosslink‐enhanced emission effect should be updated and extended to an in‐depth spatial effect, such as electron overlap and energy splitting in confined domains by effective crosslinking, more than initial immobilization. This Minireview outlines the development of the crosslink‐enhanced emission effect from the perspective of the detailed classification, inherent mechanism and applicable systems. An outlook on the further exploration and application of this theory are also proposed.

Revealing the photoluminescence (PL) origin and mechanism is a most vital but challenging topic of carbon dots. Herein, confined-domain crosslink-enhanced emission (CEE) effect was first studied by a well-designed model system of carbonized polymer dots (CPDs), serving as an important supplement to CEE in the aspect of spatial interactions. The “addition-condensation polymerization” strategy was adopted to construct CPDs with substituents exerting different degrees of steric hindrance. The effect of confined-domain CEE on the structure and luminescence properties of CPDs have been systematically investigated by combining characterizations and theoretical calculations. Such tunable spatial interactions dominated the coupling strength of the luminophores in one particle, and eventually resulted in the modulated PL properties of CPDs. These findings provide insights into the structural advantages and the PL mechanism of CPDs, which are of general significance to the further development of CPDs with tailored properties.

Greenhouse eggplant monocropping in China has contributed to the aggravation of soil-borne diseases, reductions in crop quality and yield, and the degradation of physical and chemical soil properties. Crop rotation is one effective way of alleviating the problems of continuous cropping worldwide; however, few studies have reported changes in soil bacterial community structures and physical and chemical soil properties after Brassica vegetables had been rotated with eggplant in greenhouses. In this experiment, mustard-eggplant (BFN) and oilseed rape-eggplant (BFC) rotations were studied to identify changes in the physicochemical properties and bacterial community structure in soil that was previously subject to monocropping. Samples were taken after two types of Brassica plants incorporated into soil for 15 days to compare with continually planted eggplant (control, CN) and chemical disinfection of soil (CF) in greenhouses. MiSeq pyrosequencing was used to analyze soil bacterial diversity and structure in the four different treatments. A total of 55,129 reads were identified, and rarefaction analysis showed that the soil treatments were equally sampled. The bacterial richness of the BFC treatment and the diversity of the BFN treatment were significantly higher than those of the other treatments. Further comparison showed that the bacterial community structures of BFC and BFN treatments were also different from CN and CF treatments. The relative abundance of several dominant bacterial genera in the BFC and BFN treatments (such as Flavobacteria, Stenotrophomonas, Massilia and Cellvibrio, which played different roles in improving soil fertility and advancing plant growth) was distinctly higher than the CN or CF treatments. Additionally, the total organic matter and Olsen-P content of the BFC and BFN treatments were significantly greater than the CN treatment. We conclude that Brassica vegetables-eggplant crop rotations could provide a more effective means of solving the problems of greenhouse eggplant monocultures.

We have developed a tungsten disulfide (WS2)/multiwall carbon nanotubes (MWCNTs) nanocomposite based QCM gas sensor for (trimethylamine) TMA gas sensing of low concentrations. WS2/MWCNTs nanocomposite was synthesized via the hydrothermal method and was characterized for surface morphology, nanostructure, thermal stability, and elementary composition. The TMA-sensing properties of WS2/MWCNTs nanocomposite based QCM sensor were investigated. The composite based QCM sensor showed faster response time, strong response amplitude, good gas capacity, and good selectivity and stability compared with as prepared WS2 and MWCNTs-1 based QCM sensor. The response time of WS2/MWCNTs based QCM sensor was 294.1 and 142.9 s shorter than WS2 and MWCNTs-1 for 500 ppb TMA gas. And the response of the WS2/MWCNTs based QCM sensor was almost stable over 40 days, and the limit of detection (LOD) was 76 ppb calculated by the ICH method. This was ascribed to the fact that MWCNTs provided a skeleton for the growth of WS2 nanosheets and avoided agglomeration. The special structure could not only improve the structure ability but also expose more active adsorption sites. In order to further investigate the adsorption mechanism of the TMA molecule on (pure/functionalized) WS2 materials, density functional theory (DFT) calculations based on first-principle were conducted in the Vienna Ab-initio Simulation Package under ideal conditions.

The crosslink‐enhanced emission effect was first proposed to explore the strong luminescence of nonconjugated polymer dots possessing only either non‐emissive or weakly emissive sub‐luminophores. Interesting phenomena in recent research indicate such enhancement caused by extensive crosslinking appears in diverse luminescent polymers with sub‐luminophores (electron‐rich heteroatomic moieties) or luminophores (conjugated π domains). This enhancement can promote the emission from nonluminous to luminous, from weakly luminous to strongly luminous, and even convert the pathway of radiative transitions. The concept of the crosslink‐enhanced emission effect should be updated and extended to an in‐depth spatial effect, such as electron overlap and energy splitting in confined domains by effective crosslinking, more than initial immobilization. This Minireview outlines the development of the crosslink‐enhanced emission effect from the perspective of the detailed classification, inherent mechanism and applicable systems. An outlook on the further exploration and application of this theory are also proposed.

As emerging carbon‐based nanomaterials, carbon dots (CDs) are widely studied with regard to their luminescent properties. CDs obtained by the bottom‐up method exhibit polymeric characteristics after crosslinking, polymerization, and incomplete carbonization processes, herein referred to as carbonized polymer dots (CPDs). In recent years, large progress has been achieved on the room‐temperature phosphorescence (RTP) properties of CPDs. The developments and synthesis strategies for RTP CPD materials are reviewed. However, less attention has been devoted to the influence of polymeric structures on RTP of CPD materials. Polymer structures are a common feature of CPD materials. The extensive polymer structures are the key factors facilitating the RTP of CPD materials. Herein, the effects of the polymer structures on the RTP emission of self‐protective CPD and matrix‐assisted CPD materials are discussed. It is considered that the polymer structures can effectively immobilize subluminophores and protect triplet excited states to facilitate the RTP emission of CPD materials. The crosslink‐enhanced emission (CEE) effect is proposed to further explain the RTP emission of CPD materials, which can provide an effective strategy to immobilize CPDs. Benefiting from CEE effect, efficient RTP can be achieved for CPD materials. The applications of CPD materials are then briefly summarized.

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