Effects of slight structural distortion on the luminescence performance in (Ca1-x Eux )WO4 luminescent materials

(Ca_1-x Eu_x )WO₄ (x = 0-21 mol%) phosphors were prepared using the classical solid-state reaction method. The influence of Eu³⁺ ion doping on lattice structure was observed using powder X-ray diffraction and Fourier transform infrared spectroscopy. Furthermore, under this influence, the luminescence properties of all samples were analyzed. The results clearly illustrated that the element europium was successfully incorporated into the CaWO₄ lattice with a scheelite structure in the form of a Eu³⁺ ion, which introduced a slight lattice distortion into the CaWO₄ matrix. These lattice distortions had no effect on phase purity, but had regular effects on the intrinsic luminescence of the matrix and the f-f excitation transitions of Eu³⁺ activators. When the Eu³⁺ concentration was increased to 21 mol%, a local luminescence centre of [WO₄ ]^2- groups was detected in the matrix and manifested as the decay curves of [WO₄ ]^2- groups and luminescence changed from single exponential to double exponential fitting. Furthermore, the excitation transitions of Eu³⁺ between different energy levels (such as ⁷ F₀ →⁵ L₆ , ⁷ F₀ →⁵ D₂ ) also produced interesting changes. Based on analysis of photoluminescence spectra and the chromaticity coordinates in this study, it could be verified that the nonreversing energy transfer of [WO₄ ]^2- →Eu³⁺ was efficient and incomplete.

Unexpected formation of scheelite-structured Ca1-xCdxWO4 (0 ≤ x ≤ 1) continuous solid solutions with tunable photoluminescent and electronic properties

Design of a solid solution with tunable functionality is an attractive strategy toward realizing novel devices with multi-functionalities. In this work, a series of Ca_1-xCd_xWO₄ solid solutions in the entire range 0 ≤ x ≤ 1 with tetragonal scheelite structure have been successfully prepared for the first time. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectroscopies indicated that all the nanocrystals have a tetragonal scheelite structure without wolframite phase. Structural refinement data revealed that the lattice volume decreased with the replacement of Ca²⁺ by Cd²⁺ ions. UV-Vis diffuse reflectance spectra indicated that optical band gap reduced with the replacement of Ca²⁺ by Cd²⁺ ions. Scanning electron microscopic (SEM) images showed that morphologies of the nanocrystals changed with the chemical compositions. The structure evolution of the solid solutions was further investigated by high-resolution transmission electron microscopy (HRTEM). Moreover, the influence of chemical compositions on the photoluminescent and electric performance has been performed and discussed. The reported synthetic approach and findings reported here are important to understand the structure and structure-property relation of scheelite-structured tungstate and molybdate compounds, which has potential applications in the design of other kinds of novel functional materials.

Cation-induced pesticide binding and release by a functionalized calix[4]arene molecular host

Ion-controlled switchable progress is very important in many biological behaviors. Here, we reported K(+)-controlled switch, this switch system exhibited excellent carbaryl (G) binding/release by fluorescent (FL), ultraviolet-visible (UV) spectrums and (1)H NMR spectroscopy. More importantly, the K(+)-controlled G binding/release switch based on C4C5 not only in the solution, but also on the surface, promising for the application for the pesticide controlled release.

Functionalization of SnO₂ crystals with a covalently-assembled porphyrin monolayer

The functionalization of micro- and nano-sized metal-oxide powders offers many advantages because of their large surface areas and, therefore, the large number of functional molecules that can be grafted onto the grain surfaces. Porphyrin molecules on large band-gap semiconducting metal oxides represent key materials for many different optical and electronic applications. Herein, we have proposed a general two-step procedure for the functionalization of metal-oxide crystals with dye-sensitizers. In particular, we functionalized SnO₂ nanoparticles with a monolayer of the bifunctional trichloro[4-(chloromethyl)phenyl]silane. Then, a monolayer of 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyne was covalently bound to the silanized SnO₂ grains. IR, UV/Vis, and luminescence measurements were used for optical characterization. The measured footprint of the grafted porphyrin molecules indicated total surface coverage of the grains. The surface electronic characterization was performed by using X-ray photoelectron spectroscopy. Emission measurements revealed two strong bands at 664.1 and 721.0 nm that were attributed to the porphyrin monolayer assembled on the surface of the SnO₂ crystals.