Hao Zhang

Abstract The first use of an organosilane as a coordinating solvent to synthesize highly luminescent (quantum yield = 47%) amorphous carbon dots (CDs) in one minute is reported. The CDs, which benefit from surface methoxysilyl groups, have a diameter of ~0.9 nm and can easily be fabricated into pure CD fluorescent films or monoliths simply by heating them at 80 ºC for 24 h. Moreover, the non‐water‐stable CDs can be further transformed into water‐soluble CDs/silica particles, which are biocompatible with and nontoxic to the selected cell lines in our preliminary evaluation. The proposed novel synthetic route is believed to provide an alternative synthesis route and should inspire more research into the origin and applications of CDs, as well as delivering CD‐based materials.

The CdTe nanoparticles were prepared in aqueous solution using different mercaptocarboxylic acids such as 3-mercaptopropionic acid (MPA) and thioglycolic acid (TGA) as stabilizing agents following the synthetic route described in ref 9. The pH-dependent photoluminescence (PL) of MPA- and TGA-stabilized CdTe nanoparticles was systematically investigated before and after addition of poly(acrylic acid) (PAA) into the CdTe solutions. Experimental results reveal that lowering the pH can increase the PL efficiency of both MPA- and TGA-stabilized CdTe. Moreover, the PL of the CdTe can further be increased in the presence of PAA in low pH range. X-ray photoelectron spectroscopy (XPS) was employed to investigate the interaction between the carboxyl groups from PAA and CdTe nanoparticles which were assembled in polymer matrix by a layer-by-layer self-assembly method to exclude interference from other species in CdTe solutions. XPS results demonstrate that the S/Te ratio of CdTe particles decreases after the addition of PAA, which strongly suggests that PAA can strongly interact with CdTe nanoparticles via the coordination between carboxyl groups and cadmium ions on the particle surface. As a result, the PL efficiency of the mercaptocarboxylic acid-stabilized CdTe nanoparticles is enhanced in acidic range.

CsPbX3 (X = Cl, Br, I) perovskite quantum dots (QDs) are potential emitting materials for illumination and display applications, but toxic Pb is not environment- and user-friendly. In this work, we demonstrate the partial replacement of Pb with Mn through phosphine-free hot-injection preparation of CsPbxMn1–xCl3 QDs in colloidal solution. The Mn substitution ratio is up to 46%, and the as-prepared QDs maintain the tetragonal crystalline structure of the CsPbCl3 host. Meaningfully, Mn substitution greatly enhances the photoluminescence quantum yields of CsPbCl3 from 5 to 54%. The enhanced emission is attributed to the energy transfer of photoinduced excitons from the CsPbCl3 host to the doped Mn, which facilitates exciton recombination via a radiative pathway. The intensity and position of this Mn-related emission are also tunable by altering the experimental parameters, such as reaction temperature and the Pb-to-Mn feed ratio. A light-emitting diode (LED) prototype is further fabricated by employing the as-prepared CsPbxMn1–xCl3 QDs as color conversion materials on a commercially available 365 nm GaN LED chip.

The effects of chemical states of Ag on the photoelectrochemical (PEC) properties of Ag−TiO2 composites were investigated with Ag(0)−TiO2 and Ag(I)−TiO2 prepared by photoreduction-thermal treatment (PRT) method. The comparison of photoaction spectra of Ag(0)−TiO2 and Ag(I)−TiO2 showed that only the Ag(0) containing samples had notable photocurrent under visible light (in the range of 400−800 nm), which was attributed to the highly dispersed Ag(0), according to the DRS, XRD and XPS measurements. During the photocurrent spectra measurements of Ag(0)−TiO2, it was demonstrated that Ag(0) was photoexcited because of plasma resonance in the visible light region, and charge separation was accomplished by the transport of photoexcited electrons from Ag(0) to the TiO2 conduction band with the simultaneous formation of Ag(I), which could be partially reduced to the initial active Ag(0) state under the following UV light irradiation. Actually, it was the interconversion of Ag(0) and Ag(I) during the alternating irradiation that avoided the rapid decay of photocurrent and ensured a durable and stable visible light-induced photocurrent. In the case of visible light degradation of methyl blue (MB), however, Ag(0)−TiO2 showed poorer photocatalytic activity than Ag(I)-containing ones. It was proposed that photoexcited Ag(I) rather than Ag(0) acted as active sites that were responsible for the enhanced photocatalytic abilities, whereas Ag(0) might contribute to the stability of the photocatalysts. Hence, the Ag−TiO2 nanocomposites can exhibit different photoelectrochemical performances under visible light with the different chemical states of Ag. This work could have significance not only in the mechanism study but also in the attempts to improve the visible light-induced photoactivities of Ag−TiO2, by tuning the chemical states of Ag species, in potential photoelectrochemical applications.