A diboron compound with both 3-coordinate boron and 4-coordinate boron centers, (5-BMes2-2-ph-py)BMes2 (1) and its monoboron analogue, (2-ph-py)BMes2 (2) have been synthesized. Both compounds are luminescent but have a high sensitivity toward light. UV and ambient light cause both compounds to isomerize to 1a and 2a, respectively, via the formation of a C-C bond between a mesityl and the phenyl group, accompanied by a drastic color change from yellow or colorless to dark olive green or dark blue. The structures of 1a and 2a were established by 2D NMR experiments and geometry optimization by DFT calculations. Both 1a and 2a can thermally reverse back to 1 and 2 via the breaking of a C-C bond, with the activation barrier being 107 and 110 kJ/mol, respectively. The N,C-chelate ligands in 1 and 2 were found to play a key role in promoting this unusual and reversible photo-thermal isomerization process on a tetrahedral boron center. Reactions with oxygen molecules convert 1a and 2a to 5-BMes2-2-[(2-Mes)-ph]-pyridine (1b) and 2-(2-Mes)-ph-pyridine (2b), respectively.

Size and morphology controlled NaYF4:Yb, Er nanocrystals were synthesized via the hydrothermal method. Polydentate ligands, such as EDTA and citrate, were used in the synthesis of cubic and hexagonal Yb3+, Er3+ codoped NaYF4 nanocrystals as a means of controlling the size and morphology of the nanocrystals. Subsequently, the particle size was found to be dependent on the nucleation rate, which, in turn, was governed by the reactant concentration, molar ratio and choice of ligand. The phase transformation from cubic to hexagonal was found to be sensitive to reaction time and reactant concentration. The upconversion photoluminescence of the nanocrystals demonstrated morphology dependence, which provides a means to characterize their crystalline quality and structure.

The effect of annealing on the upconversion luminescence of ZnO:Er3+ nanocrystals was investigated in detail. The green and the red upconverted emissions under infrared 978-nm light excitation were remarkably enhanced with an increase of annealing temperature. Moreover, for the sample annealed at 500 °C, the ratio of the intensity of 2H11/2 → 4I15/2 emission to that of 4S3/2 → 4I15/2 emission increased from less than to more than unity with an increase of the excitation density. However, the same case did not occur to the sample annealed at 700 °C, where the ratio was independent of excitation density except when the excitation density was higher than 42 700 W/cm2. This distinction was attributed mainly to the difference in energy gap between the 2H11/2 and 4S3/2 states in the two samples, originating from the local microstructure variation around Er3+ ions. In addition, a high thermal sensitivity of 0.0062/°C was obtained in the ZnO:Er3+ nanocrystals based on the temperature-dependent fluorescence intensity ratio (FIR) of the green upconverted emission, which would make this material a promising candidate for the nanoscaled thermal sensor of high accuracy and resolution.

3-Mercaptopropionic acid stabilized CdTe/CdS core/shell quantum dots (QDs) were prepared in an aqueous solution following the synthetic route of successive ion layer adsorption and reaction. The photoluminescence quantum yield of the CdTe QDs could reach 40%, from 8% of the bare core, via the control of the shell thickness. The CdTe/CdS QDs exhibited also a significant red shift of emission and excitation peaks when the shell layer grew. The experiments revealed that the CdTe/CdS QDs evolved from type I to type II core/shell structures with the increase of the shell thickness, and the evolution process is affected by the core size, shell thickness, surface quality of the core and shell, as unraveled by steady-state and time-resolved spectroscopy. The lack of photoluminescence lifetime lengthening was ascribed to the surface influence of the shell.

Experimental General consideration: All reactions were performed under an inert atmosphere of dry N 2 with standard Schlenk techniques unless otherwise noted. All starting materials were purchased from Aldrich Chemical Co. and used without further purification. THF, Et 2 O, and CH 2 Cl 2 were purified using the solvent purification system (Innovation Technologies Co.). Deuterated solvents as chloroform-d 1 (D, 99.8%), methanol-d 4 (D, 99.8%), benzene-d 6 (D, 99.5%) and methylene chloride-d 2 (D, 99.9%) (Cambridge Isotopes) were used as received without further drying. NMR spectra were recorded on a Bruker Avance 400 spectrometer (400.13 MHz for 1 H, 100.62 MHz for 13 C, 376.50 MHz for 19 F), chemical shifts are referenced to the residual solvent peaks and have been reported in parts per million (ppm) relative to TMS (1 H and 13 C) and CFCl 3 (19 F). UV-Vis spectra were recorded on a Varian Cary-3 UV-Visible spectrophotometer. Cyclic voltammetry was performed using a BAS CV-50W analyzer with a scan rate of 500 mV/s to 4 V/s and a typical concentration of 5 mg of the compounds in 3 mL DMF. The electrolytic cell used was a conventional three-compartment cell, in which a Pt working electrode, a Pt auxiliary electrode, and a Ag/AgCl reference electrode were employed. The CV measurements were performed at room temperature using 0.10 M tetrabutylammonium hexafluorophosphate (TBAP) as the supporting electrolyte and DMF as the solvent. The ferrocenium/ferrocene couple was used as the internal standard (E 0 = 0.55 V). Elemental analyses were

As an emerging potential energy source to address the energy crisis, osmotic energy has attracted increasing attention. Fast ion transport is essential for this blue energy and for other membrane-based...

Strong visible emissions of Er3+ resulting from two-photon absorption and energy transfer from the host YVO4 were observed in nanocrystalline Er3+-doped YVO4, which was prepared by a hydrothermal method using a citrate−yttrium−vanadate complex as the precursor. The nanocrystals were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV−visible absorption spectra, and photoluminescence (PL) spectra. The highly crystalline YVO4:Er3+ nanoparticles, with an average diameter of 35 nm, have a tetragonal zircon structure and can redisperse in water because of the presence of citrate ligands. We discussed in detail the visible upconversion mechanism and temperature dependence of the upconversion emission for the Er3+ ions in the YVO4 nanocrystals.

Capturing the osmotic power between seawater and river water is thought to be an effective strategy to solve the global energy crisis. The existing designs of membrane-based nanofluids with high ion selectivity exhibit the potential for osmotic energy harvesting but suffer from high resistance and fragility, which limit their practical applications. Here we employ silk fibroin, one of the strongest natural biopolymers, to fabricate an ultrathin membrane with outstanding mechanical properties. Such a membrane whose thickness is 10 nm per layer demonstrates low resistance and high ion throughput, achieving the top level of osmotic energy conversion up to 21.66 W/m2. By screening the thickness of membranes, the optimal value is found to be ∼100 nm to maximize the permeability and maintain the effective selectivity, as supported by the numerical simulation. The current system therefore provides a paradigm for the design of a high-performance energy conversion generator.