Controllable surface‐state emission from colloidal CdS quantum dots under different growth conditions

High‐quality colloidal photoluminescent CdS quantum dots (QDs) were synthesized in non‐coordinating solvent octadecene (ODE) using oleic acid (OA) as capping molecule, and characterized by powered x‐ray diffraction (XRD), transmission electron microscope (TEM), UV‐Vis absorption spectra, photoluminescence (PL) emission spectroscopy and time‐resolved emission spectroscopy. The effects of the growth time, the molar ratio of OA/Cd and Cd/S on the PL intensity from surface‐state have been investigated. We found that the surface‐state emission could be easily controlled by tuning the growth time and the molar ratio of Cd/S.     

Studies on the spin Hamiltonian parameters for Mn2+ in the ZnS nanocrystals and bulks

The spin Hamiltonian parameters (zero-field splitting D, g factors and hyperfine structure constants) are theoretically studied for Mn²⁺ in the ZnS nanocrystals and bulks from the perturbation formulae of these quantities for trigonal and cubic tetrahedral 3d⁵ clusters, respectively. The trigonal Mn²⁺ centre in the ZnS nanocrystals is attributed to the impurity–ligand bond angle related to the C₃ axis about 0.39° larger than that (≈109.47°) of an ideal tetrahedron. Almost the same g factors and hyperfine structure constants for the nanocrystals and bulks can be ascribed to similar crystal-field environments (i.e. comparable cubic field parameters Dq), nearly the same covalency (i.e. the equal covalency factors N) and the Mn²⁺ 3d–3s orbital admixture (i.e. the identical core polarisation constants κ) in both systems. The ligand orbital and spin–orbit coupling contributions are found to be important and should be included in the electron paramagnetic resonance analysis in view of significant covalency.     

Magnetic iron oxide nanoclusters with tunable optical response

We have developed a modified synthetic protocol for the growth of monodispersed, superparamagnetic, flower-like colloidal nanoclusters (CNCs), which are consisted of smaller iron oxide nanocrystals with adjustable size. We show that their optical properties can be tuned by applying an external magnetic field. The latter controls the subtle balance of the CNCs’ mutual interactions (magnetic versus electrostatic) and drives their assembly in aqueous media. Spectrophotometric measurements reveal that a diffuse reflectance maximum, in the visible range, is related to the CNCs organization. As the strength of the external magnetic field increases, in the range 160–600 G, the spectral weight of this feature shifts towards the blue region of the spectrum. The induced photonic crystal-like response entails a remarkable magneto-optical behavior, closely associated with the size-dependent characteristics of the CNCs ensemble. Such materials pave the way for promising technological implementations in photonics.     

A facile approach for decorating quantum dots deep inside of anodically grown self‐organized TiO2 nanotubes

We demonstrate here a simple but very effective approach to decorate anodically grown TiO₂ nanotubes (NTs) uniformly with CdS and PbS quantum dots (QDs) deep inside the NT walls. This approach is based on SILAR (successive ionic layer adsorption and reaction) technique assisted with evacuation of the NTs. The basic idea of evacuation is to remove air pockets trapped inside the NTs so as to clear the passage for the penetration of QD precursors down the bottom of the NTs.

     

Tetrafluoroborate Selective Electrodes on the Basis of Cations with Delocalized Charge

Screening of active substances based on styryl and trimethine cyanine dyes was carried out to prepare tetrafluoroborate ion‐selective electrodes. Correlations between the nature of the organic cation (pK_a) and working pH ranges of the sensors were studied. New tetrafluoroborate‐selective PVC membrane electrodes based on an active substance formed by the ion pair of 2‐(n‐ethylcarbazol‐3)‐ethenyl‐1,3,3‐trimethyl‐3H‐indolium and 2‐[3‐(5,6‐dimethyl‐3‐nonyl‐1,3‐benzothiazol‐2(3H)‐ylidene)propenyl]‐5,6‐dimethyl‐3‐nonyl‐1,3‐benzothiazolium with tetrafluoroborate ion were developed. The electrodes are non‐sensitive to pH in the range of 2–8 and can be used for boron determination in acidic media of 6–7 mol L^?1 H₂SO₄. The developed sensor was successfully applied for the determination of B₂O₃ in CdS(Se) nanocrystal‐doped glasses.     

Assembly‐Induced Emission of Cellulose Nanocrystals for Hiding Information

Fluorescent‐labeled cellulose nanocrystal (CNC) films have been used to record and protect information in paper materials, whereas the fluorescent materials usually suffer photobleaching. Herein, a strategy of solid‐state emission induced by the vertical assembly of CNCs was established. The assembly‐induced emission starts from the structural diffraction of CNC, whose wavelength is adjusted into the ultraviolet (UV) region for hiding information under natural light. The small diameter (≈10 nm) of CNCs then promotes the resonance between the vertically assembled CNCs and the UV light, leading to a strong blue emission with an emitting quantum efficiency as high as 13.90%. By introducing the vertical‐assembly film with a specific pattern into paper materials, an anti‐counterfeiting image is obtained under a UV radiation. Since CNCs are a kind of cellulose with high crystallinity, this material can be a wear‐resistant anti‐counterfeiting material for banknotes or other paper applications.     

Synthesis and white-light emission character of CdS magic-sized nanocrystals

Family 373 and 406 of CdS magic-sized nanocrystals(MSNCs) were synthesized by a one-pot non-injection approach and white-light emission was generated from the coexistence of them.This light had excellent color characteristics,as defined by their pure white CIE(Commission International de I’Eclairage) color coordinates(0.328,0.343),and it correlated with a color temperature of 5696 K.A probable thermodynamic equilibrium was proposed to explain the white-light emission behavior in this letter.