Abstract Due to the complex core–shell structure and variety of surface functional groups, the photoluminescence (PL) mechanism of carbon dots (CDs) remain unclear. o-Phenylenediamine (oPD), as one of the most common precursors for preparing red emissive CDs, has been extensively studied. Interestingly, most of the red emission CDs based on oPD have similar PL emission characteristics. Herein, we prepared six different oPD-based CDs and found that they had almost the same PL emission and absorption spectra after purification. Structural and spectral characterization indicated that they had similar carbon core structures but different surface polymer shells. Furthermore, single-molecule PL spectroscopy confirmed that the multi-modal emission of those CDs originated from the transitions of different vibrational energy levels of the same PL center in the carbon core. In addition, the phenomenon of “spectral splitting” of single-particle CDs was observed at low temperature, which confirmed these oPD-based CDs were unique materials with properties of both organic molecules and quantum dots. Finally, theoretical calculations revealed their potential polymerization mode and carbon core structure. Moreover, we proposed the PL mechanism of red-emitting CDs based on oPD precursors; that is, the carbon core regulates the PL emission, and the polymer shell regulates the PL intensity. Our work resolves the controversy on the PL mechanism of oPD-based red CDs. These findings provide a general guide for the mechanism exploration and structural analysis of other types of CDs.
Nitrogen and sulfur co-doped carbon dots were synthesised via Allium fistulosum, that exhibit low cytotoxicity and provide good optical stability for cell imaging.
Carbon dots (CDs), as emerging luminescent nanomaterials, possess excellent but complex properties, and thus, they have attracted immense attention for their applications. Further practical application of CDs has been hindered by their limited photostability and photoluminescence intermittency. In this study, we demonstrated that an antioxidant (Trolox) can dramatically enhance the photostability and minimize the photoblinking of CDs without affecting their native spectral characteristics. Significant photoluminescence enhancement and stabilization were observed with the addition of Trolox in ensemble level. Meanwhile, strikingly stable emissions from individual CDs have been observed in the presence of Trolox in single-particle-level experiments. Our observations revealed that the charged state of CDs can be effectively recovered to a neutral state by Trolox via electron transfer. These results prove that the combination of antioxidants and CDs is a powerful means to improve their fluorescence robustness, which is crucial for applications that demand long-lived, nonblinking emission.
The emergence of all-inorganic halide perovskites has shown great potential in photovoltaic and optoelectronic devices. However, the photo-induced phase segregation in lead mixed-halide perovskites has severely limited their application. Herein, by real-time monitoring the photoluminescence (PL) spectra of metal mixed-halide perovskites under light irradiation, we found that the photo-induced phase transition can be significantly inhibited by B-site doping. For pristine mixed-halide perovskites, an intermediate phase of CsPbBrxI3-x can only be stabilized under low excitation power. After introducing Sn2+ ions, such intermediate phase can be stabilized in nitrogen atmosphere under high excitation power and phase segregation can be started after the exposure in oxygen due to oxidization of Sn2+. Replacing Sn2+ by Mn2+ can further improve the intermediate phase's tolerance to oxygen proving that B-site doping in perovskites structure by Sn2+ or Mn2+ could effectively minimize the light-induced phase segregation and promote them to serve as promising candidates in photovoltaic and light-emitting devices.
Ionic movement inside organometal halide perovskites (OMHP) materials has been widely reported to be linked with stability issues in the perovskite-based optoelectronic devices. However, the dynamic processes of the ionic movement and how they influence the devices are still not well-understood. In this work, we applied an external electric field to the CH3NH3PbI3 crystal and simultaneously monitored the PL behaviors. Two successive PL responses were observed in the same location of the crystal. First, an irreversible PL quenching was observed caused by the photo-annealing effect under an electric field accompanied by a permanent morphology change. The annealed area also showed reversible PL variation, which was attributed to the activation–deactivation of the radiative recombination centers induced by the migration of the iodine ions. Such results can help us gain a deep insight into how the ionic movements in OMHPs influence the performance of the perovskite-based optoelectronic devices under working conditions.
Biofilms formed on urinary catheters remain a major headache in the modern healthcare system. Among the various kinds of biocide-releasing urinary catheters that have been developed to prevent biofilm formation, Ag nanoparticles (AgNPs)-coated catheters are of great promising potential. However, the deposition of AgNPs on the surface of catheters suffers from several inherent shortcomings, such as damage to the urethral mucosa, uncontrollable Ag ion kinetics, and unexpected systematic toxicity. Here, AgNPs-decorated amphiphilic carbonaceous particles (ACPs@AgNPs) with commendable dispersity in solvents of different polarities and broad-spectrum antibacterial activity are first prepared. The resulting ACPs@AgNPs exert good compatibility with silicone rubber, which enables the easy fabrication of urinary catheters using a laboratory-made mold. Therefore, ACPs@AgNPs not only endow the urinary catheter with forceful biocidal activity but also improve its mechanical properties and surface wettability. Hence, the designed urinary catheter possesses excellent capacity to resist bacterial adhesion and biofilm formation both in vitro and in an in vivo rabbit model. Specifically, a long-term antibacterial study highlights its sustainable antibacterial activity. Of note, no obvious toxicity or inflammation in rabbits was triggered by the designed urinary catheter in vivo. Overall, the hybrid urinary catheter may serve as a promising biocide-releasing urinary catheter for antibacterial and antibiofilm applications.
The development of clean fuels for hydrogen utilization will benefit from low-cost and active catalysts to produce hydrogen via hydrolytic dehydrogenation by electrochemical and chemical means. Herein, we designed and synthesized a high-efficiency and stable catalyst with low-ruthenium content CoRu alloy nanoparticles supported on porous nitrogen-doped graphene layers (CoRux@N-C) via pyrolysis of small organic metal molecules. The amount of ruthenium in the catalyst that showed the highest activity was only 5.07 wt %. CoRu0.25@N-C can efficiently catalyze the hydrogen evolution reaction (HER) with a wide pH range and low overpotential to drive current densities of 10 mA·cm–2 of only 27 mV (1.0 M KOH) and 94 mV (0.5 M H2SO4). CoRu0.25@N-C also showed decent durability with negligible degradation after 1000 cyclic-voltammetry cycles in both acidic and alkaline solutions. It also has excellent catalytic activity and can easily sustain ammonia borane hydrolysis with an initial turnover frequency (TOF) of 457.8 molH2 min–1 molcat–1 under ambient conditions. CoRu0.25@N-C can readily perform both NH3BH3 hydrolytic dehydrogenation and electrochemical hydrogen evolution as a result of its highly specific surface area, carbon layer protection, metal vacancies, and a porous carbon matrix doped with heteroatoms. The creation of a multifunctional composite/hybrid by the use of small metal organic molecules can lead to cost-effective and highly efficient catalysts for energy conversion.
Since the first optical detection of single molecules in 1989, single-molecule spectroscopy has developed rapidly and been widely applied in many areas. However, the vast majority of matter is extremely inefficient at emitting photons in our physical world, which seriously limits the applications of optical methods based on photoluminescence. In addition to indirect detection by fluorescence labeling, many efforts have been made to directly image nonfluorescent matter at the single-particle or single-molecule level in different ways based on the absorption or scattering interaction between light and matter. Herein, we review five popular methods for imaging nonfluorescent particles/molecules, including dark-field microscopy (DFM), surface plasmon resonance microscopy (SPRM), surface enhanced Raman microscopy (SERM), interferometric scattering microscopy (iSCAT), and photothermal microscopy (PTM). After summarizing the principles and applications of these methods, we compare the advantages and disadvantages of each method and describe further potential development and applications.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)