Improvement of the photostability for YVO4:Bi,Eu nanoparticles synthesized by the citrate route

YVO₄:Bi³⁺,Eu³⁺ nanophosphor synthesized by the citrate route shows the photobleaching behavior, i.e., the decrease in photoluminescence intensity under the continuous irradiation of excitation light. This photobleaching property is remarkably suppressed by the washing post-treatment combined with centrifugation and the hydrothermal post-treatment. A relation between the fraction of photobleach and the amount of citrate ions coordinating to metallic ions at the surface of nanoparticles verifies that the photobleaching behavior of YVO₄:Bi³⁺,Eu³⁺ nanophosphor originates from the redox reaction between the citrate ions and V⁵⁺ in YVO₄ host crystal. The long-term light fastness test reveals that the hydrothermally treated YVO₄:Bi³⁺,Eu³⁺ nanophosphor has sufficient photostability for practical use over 15 years outside.     

Yolk-shell CdS@void@TiO2 composite particles with photocorrosion resistance for enhanced dye removal and hydrogen evolution

Yolk-shell CdS@void@TiO₂ (cadmium sulfide@void@titanium dioxide) composite particles (CPs), consisting of three parts: core (CdS) synthesized by solvent thermal reaction, void generated by polypyrrole (PPy) sacrificed layers and porous shell (TiO₂) by sol-gel method, were innovatively fabricated. The actual yolk-shell structure and chemical composition of the resultant CdS@void@TiO₂ were verified by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray powder diffraction analyses (XRD), and X-ray photoelectron spectroscopy (XPS). CdS@void@TiO₂ CPs possessed enhanced visible light response due to its narrower energy gap (2.9 eV) than TiO₂ (3.2 eV). With the support of photocatalytic performance test results, CdS@void@TiO₂ exhibits much higher hydrogen evolution rate up to 1893.5 μmol h⁻¹ g⁻¹ as well as dye removal efficiency both under visible and UV light irradiation than pristine TiO₂. The covering of TiO₂ shell remarkably promotes the photocorrosion resistance of CdS. The unique yolk-shell structure promotes striking photocatalytic performance in dye removal and hydrogen evolution. A possible photocatalytic mechanism about enhanced photocatalytic activity and robust photostability is also proposed.     

双功能受阻胺与紫外线吸收剂并用的协同效应研究

本文用IR、UV、ESR、TLC等方法研究了新型的双功能受阻胺光稳定剂,Tinuvin-144 [2-(4′-羟基-3′,5′-二叔丁基)苄基-2-正丁基丙二酸五甲基哌啶醇酯]与紫外线吸收剂,UV-531(2-羟基-4-正辛氧基二苯甲酮)和UV-327(2-[2′-羟基-3′,5′-二叔丁基]-5-氯 代苯并三唑)并用体系对聚丙烯光稳定化的并用效应。结果表明,Tinuvin-144与UV-531,UV-327并用时均具有良好的协同效应,144对531,327或531,327对144的光分解均具有相互的保护作用。结果还表明,144与531或327无论在模拟体系或聚丙烯中,在诱导期内均不存在促使他们消耗的化学反应,提出了协同作用的机理。     

Concentration effects on emission of bay-substituted perylene diimide derivatives in a polymer matrix

Reduction of emission quenching in a gain medium based on a dye-doped organic matrix at high doping concentrations is of crucial importance for achieving efficient lasing with a low threshold. In this study, concentration effects on emission properties of bay-substituted perylene diimide derivatives, considered to be promising for lasing application, are reported. Dynamics of emission spectra, quantum yield, lifetime, amplified spontaneous emission, amplified spontaneous emission threshold and photostability of the bromo-, 2,4-di(trifluoromethyl)phenyl- and 4-pyridyl-substituted perylene diimide derivatives in polystyrene films are explored in a wide range of diimide concentrations from 0.06 wt % to 8 wt %. For comparison, emission properties of an unsubstituted perylene diimide derivative are also investigated. An importance of the bay substitution in the perylene diimides is emphasized through i) reduction of emission concentration quenching, which allows for 3-4 times higher doping levels as compared to the doping with an unsubstituted perylene diimide, ii) observation of amplified spontaneous emission at one order of magnitude higher concentrations with reasonable thresholds (up to 200-300 kW/cm²), and iii) high photostability, which is one order of magnitude higher than that of other bay-substituted perylene diimides and various organic compounds. The results imply potential of the perylene diimide substitution at the bay position for tailoring molecular packing and emission properties via steric hindrance effects, and suggest the bay-substituted perylene diimides may be useful as active media for lasing applications.     

Metal enhanced fluorescence of the fluorescent brightening agent Tinopal-CBX near silver island film

Metal-enhanced fluorescence (MEF) studies of the optical brightener Tinopal-CBS (4,4′- distyrylbiphenyl sulfonic sodium salt) have been undertaken using steady-state and time resolved fluorescence measurements on silver island films (SiFs) deposited on glass slides and silver nano-particles adsorbed onto cellulose based filter paper. Nearly a 4.5 fold enhancement in fluorescence intensity is observed from both SiFs and nano-particle deposited cellulose filter paper. In addition an enhanced photostability and decrease in decay time is also observed on SiFs. These results are consistent with two distinct mechanisms of MEF, firstly coupling and transferring of the excited states energies of fluorophores to surface plasmons in the silver island deposited glass films, and secondly, an electric field enhancement effect, which facilitates enhanced absorption of the fluorophores. Our findings reveal significant benefits of enhanced luminescence and prolonged photostability of Tinopal CBS. As such, Plasmon-tinopal constructs offer new material opportunities as well as multifarious applications in the life sciences.     

Glucose-mediated solution-solid route for easy synthesis of Ag/ZnO particles with superior photocatalytic activity and photostability

In this paper, we report an effective glucose-assisted solution-solid process for preparing Ag/ZnO photocatalyst with excellent photocatalytic performance. The solution-solid route included first formation of a glucose-Zn-Ag precursor containing Zn and Ag source in glucose framework (solution-phase stage) and subsequent heat treatment of the precursor to obtain Ag/ZnO particles (solid-phase stage). Ag/ZnO particles could be prepared on large scale through this solution-solid process (about 1.5 g for each time synthesis and could be easily scaled up). Also, the result of photocatalytic test indicates that the material exhibits superior photocatalytic activity for the photodegradation of organic dye Rhodamine B. Notably, no obvious loss of catalytic activity was observed after ten cycles, indicating the excellent photostability of Ag/ZnO particles.     

Synthesis of highly photo-stable CuInS2/ZnS core/shell quantum dots

CuInS₂ quantum dots are considered near-ideal fluorophores based on their bright emission and low toxicity. However, CuInS₂ quantum dots are still bothered by their sensitivity to surface chemistry and chemical environment. Traditionally, the CIS QDs require an additional coating process to be encapsulated inside silica sphere or organic polymer. Up till now, few works have been made concerning improving the intrinsic stability of CIS QDs. In an effort to improve the stability of CuInS₂ quantum dots, we came up with a new method by increasing the ZnS shell thickness. These QDs were characterized by photoluminescence, HRTEM, XRD and XRF analysis. We investigated the influence of ZnS shell thickness on the ambient stability of CIS/ZnS QDs. The results demonstrated that a thicker ZnS shell helped significantly improve both photostability and chemical stability of the QDs. Finally, the thick shell QDs were dispersed into transparent polymer matrix and fabricated into a LED device, which also gave much more stability compared with conventional QDs.     

Photophysical properties and photostability of novel symmetric polycyclicphenazine-type fluorescent dyes and the dye-doped films

Novel symmetric polycyclicphenazine-type fluorescent dyes have been synthesized and characterized in solution and in polymer films. The dyes exhibited two strong absorption bands at around 365-428 nm and 519-567 nm and an intense fluorescence band at around 560-600 nm (Ф = 0.70-0.87) in 1,4-dioxane. The dye-doped polymer films showed excellent wavelength conversion function that efficiently convert ultraviolet and yellow lights into red light (Ф = 0.61-0.92). Moreover, the photostability of the dye-doped PS, PMMA, and PLA films has been investigated.     

Spectroscopic properties and amplified spontaneous emission of fluorescein laser dye in ionic liquids as green media

The use of ionic liquids (ILs) as milieu materials for laser dyes is a promising field and quite competitive with volatile organic solvents and solid state-dye laser systems. This paper investigates some photo-physical parameters of fluorescein dye incorporated into ionic liquids; 1-Butyl-3-methylimidazolium chloride (BMIM Cl), 1-Butyl-3-methylimidazolium tetrachloroaluminate (BMIM AlCl₄) and 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIM BF₄) as promising host matrix in addition to ethanol as reference. These parameters are: absorption and emission cross-sections, fluorescence lifetime and quantum yield, in addition to the transition dipole moment, the attenuation length and oscillator strength were also investigated. Lasing characteristics such as amplified spontaneous emission (ASE), the gain, and the photostability of fluorescein laser dye dissolved in different host materials were assessed. The composition and properties of the matrix of ILs were found that it has great interest in optimizing the laser performance and photostability of the investigated laser dye. Under transverse pumping of fluorescein dye by blue laser diode (450 nm) of (400 mW), the initial ASE for dye dissolved in BMIM AlCl₄ and ethanol were decreased to 39% and 36% respectively as time progressed 132 min. Relatively high efficiency and high fluorescence quantum yield (11.8% and 0.82% respectively) were obtained with good photostability in case of fluorescein in BMIM BF₄ that was decreased to ∼56% of the initial ASE after continuously pumping with 400 mW for 132 min.