Fabrication of complexed nanostructure using AAO template for ultrasensitive SERS detection.

In the study of surface-enhanced Raman scattering (SERS) processes, a simple and fast approach is needed to ensure the large-scale preparation of SERS substrates. This article uses anodic aluminum oxide (AAO) as a template to assemble gold nanoparticles (Au NPs) into an ordered array. By changing the pore size of AAO and silanizing the pores, the number and density of Au NPs entering the pores through liquid-liquid two-phase self-assembly (LLSA) can be effectively regulated. Using Rh6G (Rhodamine 6G) and CV (Crystal Violet) molecules as probe molecules, substrate sensitivity was evaluated with an enhancement factor of up to 6.34 × 107. In addition, the uniformity of the substrate is good, with a relative standard deviation (RSD) of 9.94%, and the logarithmic concentration and the Raman signal presented significant linear correlations R2 was 0.997 and 0.985, respectively. The detection limit of the substrate for APM (aspartame) as a solvent is as low as 0.0078 g/L. Finally, the substrate was subjected to high sensitivity testing on two types of beverages containing APM sold, proving the practicality of the substrate. It is expected to achieve simple and rapid detection in food additive trace detection in the future.

Synthesis and Phase Behavior of (Semifluorinated Alkane)-Based Side-Chain Liquid Crystalline Copolymers.

Side-chain liquid crystalline polymer (SCLCP) usually contains a simple and flexible homopolymer as main chain, while its effect on the self-assembly behavior is often ignored. In this work, in order to increase the structural complexity and investigate the interaction between the main chain and mesogens, perfluorinated segments are introduced into the main chain using a photoinduced Step Transfer-Addition & Radical-Termination polymerization method, producing a novel series of SCLCPs containing 4-methoxyphenyl benzoate mesogens, soft hydrocarbon spacers, and a strictly alternating perfluoroalkyl and alkyl backbone. By adjusting the length of spacers or perfluoroalkyl segments, several mesophases with complex chain packing structures are achieved. This design strategy that constructing highly ordered liquid crystalline (LC) structures from SCLCPs with precise chemical structure provides a facile way toward novel LC nanomaterials.

An alternating conduction-insulation "molecular fence" model from fluorinated metallopolymers.

Introducing fluoroalkyl chains into metallopolymers is a prerequisite to studying the self-organization effect of fluoroalkyl chains and their structure-property relationship. In this work, we present a fluorinated metallopolymer to build an alternating conduction-insulation "molecular fence" model synthesized by the coordination of Ru(II) and a bis-terpyridine-end-capped-phenyl (BTP) ligand modified with fluoroalkyl chains. Taking advantage of scanning tunneling microscopy (STM), a well-aligned periodic linear layered structure is observed clearly, which provides the most direct visualization of the self-organization effect of fluoroalkyl chains for the first time. In addition, combining ultraviolet-visible (UV-vis) absorption spectroscopy and theoretical calculations, we find that fluoroalkyl chains demonstrate a septation effect between two adjacent metallopolymer chains and further restrain the occurrence of interchain charge-transfer transition (ICCT) due to their closed packed structure. This "molecular fence" model can provide a novel route for electron conduction in molecular networks and guide potential applications in the materials science field.

Facile photochemical synthesis of main-chain-type semifluorinated alternating copolymers catalyzed by conventional amines or halide salts.

In this work, we report a much simpler and low-cost method to prepare main-chain-type semifluorinated alternating copolymers by the formation of a halogen bond (XB) complex between α,ω-diiodoperfluoroalkanes and amines/halide salts. It is interesting that the terminal iodine functional group of the polymer chains is easily lost in the amine-promoted system, while the loss can be significantly reduced by adding a small amount of water. Importantly, the system promoted by halide salts can ensure complete retention of the iodine functional group. Overall, the establishment of this method provides a new strategy for designing smart fluoropolymer materials in a green and environmentally friendly facile manner under irradiation with visible light at room temperature.

Reduction-Induced Crystallization-Driven Self-Assembly of Main-Chain-Type Alternating Copolymers: Transformation from 1D Lines to 2D Platelets.

In recent years, crystalline-driven self-assembly (CDSA) has received enormous attention, but almost only for block copolymers (BCPs). Herein, we introduced perfluorocarbon chains into main-chain-type liquid crystalline alternating copolymers (ACPs) to obtain perfluoroalkane-containing ACPs with periodic C-I bonds in polymer backbones via step transfer-addition and radical-termination (START) polymerization, followed by an iodine reduction reaction of C-I bonds to induce CDSA of ACPs and put forward a novel concept of "reduction-induced crystallization-driven self-assembly" (RI-CDSA) of main-chain-type ACPs for the first time. Finally, we proposed the folded-chain model and mechanism to explain the novel RI-CDSA behavior, and its rationality has been proved by the corresponding experimental results.

Unique adjustable UC luminescence pattern and directional radiation of peculiar-shaped NaYF4: Yb3+/Er3+ microcrystal particle.

A new design of peculiar-shaped ß-NaYF4: 20% Yb3+/2% Er3+ hexagonal microcrystal (PSßHM) is proposed and its upconversion (UC) luminescence with adjustable color pattern is studied with near infrared excitation. Flower-like green UC luminescence emission pattern from blooming to withering process and intensive directional red emission are achieved by simply adjusting the focal point position of the excitation light. The mechanism that determines the unique UC luminescence phenomena are investigated systematically. The function of the internal light reflection and waveguide effect with annular microcavity is explored based on the structure characteristic of the hexagonal microplate. The current work may have great significant and potential applications in the development of optoelectronic device, color display, directional light and laser emission of microsystem.

Ag@SiO2/LaF3:Eu3+ Composite Nanostructure and Its Surface Enhanced Luminescence Effect.

Ag@SiO2/LaF3:Eu3+ core-shell nanostructure was synthesized with a wet chemical method in which the SiO2 layer functioned as a separation layer between Ag-core and LaF3:Eu3+ luminescence material. With this system, surface enhanced luminescene of LaF3:Eu3+ with Ag substrate was investigated, and an obvious enhancement effect was observed. The dependence of the luminescence enhancement on the distance between the luminescence shell and the metallic core was studied too. It is believed that the enhancement effect presented by the current hybrid nanostructure system has great potential in the development of photovoltaic cells.

Enhancement and regulation of fluorescence emission from NaYF4:Yb3+, Er3+ nanocrystals by codoping Mn2+ ions.

NaYF4:Yb3+, Er3+, Mn2+ nanocrystals with cubic crystal phase were obtained by a facile solvothermal method through doping a proper amount of Mn2+ ions to the nanocrystals. The results of XRD and TEM showed that the as-prepared samples were well crystallized and their average size was about 25 nm. Under excitations at 978.5 nm and at 532 nm, obvious enhancement and regulation of upconversion and downconversion fluorescence were obtained. Upconversion emission spectra indicate that these effects were independent of doped concentrations of Er3+ and Yb3+, excitation power, and the excitation wavelength in the current study. It is concluded that the enhancement of fluorescence emissions is mainly due to the change of local symmetry around Er3+ ions, while the regulation of red-to-green ratios was caused by efficient energy transfer between Er3+ and Mn2+ ions. This kind of upconversion material has a great potential in bioimaging and drug delivery since the excitation and emission falls into the region of "optical window" of biological tissues.

Pr3+/Yb3+ co-doped beta-phase NaYF4 microprisms: controlled synthesis and upconversion luminescence.

Pr3+/Yb3+ co-doped hexagonal NaYF4(beta-NaYF4) microprisms were synthesized by the hydrothermal method, and ethylenediaminetetraacetic acid (EDTA) was introduced to control the size of the microcrystal samples. Bright upconverted fluorescence emission was observed when the samples were excited with an infrared (IR) laser at 976.4 nm. The emission was found to originate from the transitions of 3P0-3F2, 3P0-3H6 or 1G4-3H4, 3P1-3H6, 3P0-3H5, 3P1-3H5, and 3P0-3H4 of Pr3+ ions. Possible mechanisms for upconversion fluorescence and concentration dependence as well as the crystal structure and its formation of NaYF4:Yb3+/Pr3+ microprisms were explored and discussed based on the experimental observations.

Facile fabrication and upconversion luminescence enhancement of LaF3:Yb3+/Ln3+@SiO2 (Ln = Er, Tm) nanostructures decorated with Ag nanoparticles.

A novel hybrid nanostructure, that is a Ag nanoparticle decorated LaF(3):Yb(3+)/Ln(3+)@SiO(2) nanosphere (Ln=Er, Tm), was constructed by a facile strategy, and characterized by XRD, TEM, FTIR, XPS and UV-vis-NIR absorption. Obvious spectral broadening and red-shift on the surface plasmon resonance were obtained by adjusting the size and configuration of Ag nanoparticles. Effective upconversion luminescence enhancements for Er(3+) and Tm(3+) containing samples were obtained. It is suggested that the luminescence enhancement results from both the excitation and emission processes, and the configuration of the studied hybrid nanostructure is an efficient system to enhance the luminescence emission of rare earth doped nanomaterials. It is believed that the enhancement from the hybrid nanostructure will find great potential in the development of photovoltaic solar cells.

The influence of synthesizing processes on the spectroscopic property of tetragonal LaOF:Eu3+ nanoparticles.

The tetragonal LaOF:Eu3+ nanoparticles have been successfully synthesized by three different methods including hydrothermal, solvothermal and chemical precipitation methods. Strong red fluorescence emissions were observed by exciting the samples with 532 nm laser. Under the proper conditions, the sample synthesized via chemical precipitation method presented the strongest fluorescence emission. It is found that the particle size, surface modification, crystal structure and local environment could be adjusted with different preparation processes.

Strong photoluminescence through up and down conversion in Tm(3+)/Ho(3+):LaOF nanoparticles.

Efficient up and down frequency conversions in Tm(3+) and Ho(3+) doped LaOF tetragonal nanocrystals have been investigated. Bright fluorescence emissions are obtained in co-doped Tm(3+)/Ho(3+):LaOF tetragonal nanocrystals through UV and infrared excitation. Green florescence from doped Ho(3+) ions, which can be clearly seen with bared eyes, is obtained when Tm(3+) ion is excited. Specific mechanism of the cross relaxation between doped ions is explored through spectroscopic measurements in time and frequency domains. About 90% energy transfer efficiency is obtained when the weak radiative and nonradiative relaxations are neglected.

Influence of crystal structure on the fluorescence emission of Eu3+:LaOF nanocrystals.

Optical transitions of Eu(3+)-doped LaOF nanocrystals with tetragonal and rhombohedral structures were studied experimentally using laser spectroscopic method. Fluorescence emissions from 5D1 and 5D0 of Eu3+ in LaOF nanocrystals were detected by exciting the sample with a 532 nm pulsed laser, and the influence of local symmetry on the fluorescence emission of doped ions was observed. The specific crystalline phase as well as the local symmetry on the fluorescence emission was investigated in both the frequency domain and time domain. It was found that Eu3+ ions doped in the tetragonal crystal structure present more efficient fluorescence emission, which was explained by lower symmetric distribution of local field at the doped ions.

Investigation of radiative and nonradiative relaxation by two-photon resonant excitation in Tm3+ doped LaF3 particles.

Nano-scaled and micro-scaled Tm(3+)-doped LaF3 were prepared by a hydrothermal technique. Two-photon resonant excitation from the ground state 3H6 to the excited state 1D2 was fulfilled by two pulsed dye lasers tuned at 656 nm and 643 nm, respectively, which were resonant with the ground state absorption of 3H6 --> 3F2 and the excited state absorption of 3H4 --> 1D2. The time evolution of the corresponding state was investigated with blue upconverted emission by tuning the delay of two excitation lights. The results showed that the nonradiative relaxation of the 3F2 state was mainly affected by the confinement effect, while the radiative relaxation of 3H4 state was significantly influenced by the Tm3+ concentration.

Local-field effect on the fluorescence relaxation of Tm3+:LaF3 nanocrystals immersed in liquid medium.

Tm(3+):LaF(3) nanocrystals were synthesized with hydrothermal technique. Local-field effect on the radiative relaxation rate was studied in the system of Tm(3+):LaF(3) nanocrystals immersed in several liquid media. The fluorescence lifetime was measured. It was found that the fluorescence decay presented the characteristics of second-order exponential decay, for which the contribution from the ions inside the nanocrystal and ions at the interface of the nanocrystal were distinguished. Investigating the experimental results with proposed models, we found that the surface effect had to be eliminated. For rare earth doped LaF(3) nanocrystals, real-cavity model well explains the influence of surrounding medium on the fluorescence relaxation rate.