聚芴类半导体光谱稳定性

有机半导体的物理和化学性质直接影响其光电器件的性能, 这为物理化学提出了新的研究内容与挑战. 其中, 聚芴类蓝光二极管的光谱稳定性及低能发射带(LEEB)的起源问题是国际上近十年的热点问题之一. 本文系统概述了低能发射带的现象、表征方法以及可能的形成机理, 包括链间作用导致的激基缔合物发射、器件制备或降解过程形成的芴酮缺陷发射、芴酮聚集态发射以及聚芴端羟基界面氧化导致的绿光发射. 本文综述各种物理掺杂和界面调控改善聚芴类二极管蓝光稳定性的策略, 着重论述非平面基团的空间位阻、分子构象与链的拓扑结构以及引入抗氧化受阻胺光稳定剂来提高其光谱稳定性策略.     

有机膨润土负载ZnO/TiO2光降解催化剂的研制及性能

以六水硝酸锌、酞酸丁酯和有机膨润土为原料,采用沉淀法制备ZnO/TiO2膨润土复合光催化材料,用IR和XRD对光催化剂的组织构造和微观结构进行表征,实验了光催化剂对亚甲基蓝废水的降解性能。结果表明：ZnO/TiO2成功负载于膨润土片层表面,ZnO的含量为有机膨润土的8%,反应温度为70℃,焙烧温度为420℃,催化剂用量为12mg/L时,亚甲基蓝废水的降解率可达97%以上。     

Electroluminescence of colloidal ZnSe quantum dots

The article reports a green chemical synthesis of colloidal ZnSe quantum dots at a moderate temperature. The prepared colloid sample is characterised by UV-vis absorption spectroscopy and transmission electron microscopy. UV-vis spectroscopy reveals as-expected blue-shift with strong absorption edge at 400 nm and micrographs show a non-uniform size distribution of ZnSe quantum dots in the range 1-4 nm. Further, photoluminescence and electroluminescence spectroscopies are carried out to study optical emission. Each of the spectroscopies reveals two emission peaks, indicating band-to-band transition and defect related transition. From the luminescence studies, it can be inferred that the recombination of electrons and holes resulting from interband transition causes violet emission and the recombination of a photon generated hole with a charged state of Zn-vacancy gives blue emission. Meanwhile electroluminescence study suggests the application of ZnSe quantum dots as an efficient light emitting device with the advantage of colour tuning (violet-blue-violet).     

High power efficiency in single layer blue phosphorescent organic light-emitting diodes

High efficiency single layer blue phosphorescent organic light-emitting diodes (PHOLEDs) without any charge transport layer were developed. A mixed host of spirobifluorene based phosphine oxide (SPPO13) and 1, 1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) was used as the host in the emitting layer. A high maximum external quantum efficiency of 15.8% and a quantum efficiency of 8.6% at 1000 cd/m² were achieved in the single-layer blue PHOLEDs without any charge transport layer. The maximum power efficiency and power efficiency at 1000 cd/m² were 31.4 and 16.9 lm/W, respectively.     

Luminescence efficiencies of self- and Tm activated CaWO4 under vacuum ultraviolet radiation excitation

Luminescence efficiency of self-activated CaWO₄ under 147 nm vacuum ultraviolet (VUV) radiation excitation is about 90% of that of BaMgAl₁₀O₁₇:Eu²⁺ (BAM), the commercial blue plasma display panel (PDP) phosphor. However, the color purity and the particle size of the former needs substantial modification before it can be considered for application in PDP. CaWO₄:Tm exhibits Tm³⁺ emission peaks in the blue region due to energy transfer from WO₄ to Tm³⁺ ions but the overall emission intensity under 147 nm excitation is reduced when compared to that of CaWO₄.     

A new synthetic pathway of Sr2CeO4 phosphor and its characterization

A blue-white emitting Sr₂CeO₄ phosphor was synthesized via a simple sol-gel poly vinyl alcohol (PVA)-complexing process using strontium nitrate and cerium nitrate as raw materials. The samples were characterized by TG/DTA, XRD, FTIR, SEM and photoluminescence spectroscopy. The X-ray diffraction study confirms the structure of the system to be orthorhombic. The emission spectra when excited at 267 nm peaks at ∼470 nm. The emission band is assigned to the energy transfer between the molecular orbital of the ligand and charge transfer state of the Ce⁴⁺ ion. The Commission International de l'Eclairage (CIE) co-ordinates for the Sr₂CeO₄ sample were also calculated.     

High-resolution spectroscopy of the ν8 band of methylene bromide using a quantum cascade laser

A continuous wave cavity ringdown spectrometer with a Fabry-Perot quantum cascade laser has been used to collect a rotationally-resolved infrared spectrum of the ν₈ vibrational band of methylene bromide in a slit nozzle expansion. In our laboratory, previous observations of the vibrational band were limited by spectral coverage to only the P and Q-branches and by the 24 MHz step-size of the laser [1]. The issue of limited spectral coverage has been resolved using a Fresnel rhomb and a wire grid polarizer to protect the laser from the destabilizing effects of back-reflection from the ringdown cavity. The frequency step-size of the spectrometer has been reduced from 24 MHz to 2 MHz. With both of these instrument enhancements, we have been able to record the R-branch of the vibrational band, and can resolve many lines that were previously blended in spectra acquired using a pinhole expansion nozzle. Significant hyperfine splitting was observed for the low-J transitions in the P and R-branches. It was possible to neglect the effects of hyperfine splitting for transitions involving J″ > 2 in the spectral assignment, and simulations using the constants obtained by fitting to Watson’s S-reduced Hamiltonian for CH₂⁷⁹Br⁸¹Br, and the A-reduced form for CH₂⁷⁹Br₂ and CH₂⁸¹Br₂, provide a good match to experimental spectra. A total of 297 transitions have been assigned for all three isotopologues, with a standard deviation of 0.00024 cm⁻¹(∼7 MHz).     

Adsorption of Methylene Blue on Montmorillonite

ABSTRACT

Adsorption of Methylene Blue ( MB) on Na-, Fe- and Al-montmorillonite suspensions at 298.15 K were studied. The effect of different exchangeable cation on the adsorption amount of MB was determined. The results show that methylene blue cations( MB⁺ ) replace Na? more easily than they do Fe³⁺ and Al^{3 +} The adsorption isotherms on the three montraorillonites were all of Langmuir type, except that the isouHerm of MB on Na-montmorillonite presents nonmonotonic curve at low surface coverage. The specific surface areas in suspension were calculated by( MB ^{3 +} )method, and Na^? is more effective to determine the specific surface area by MB method in suspension than Fe^{3 +} and A^{3 +} The discrepancy of the specific surface area measured by MB and BET method was discussed.     

Dependence of photoluminescence of CdSe/ZnS on excitation wavelength

We have found that the photoluminescence (PL) intensity of CdSe/ZnS nanocrystals placed on a thin film of insulator (GaAsOx/GaAs) depends on excitation wavelength through the interference effects of the excitation light. By employing the multi-reflection/interference calculation, the insulator thickness of the underlying non-uniform patterns can be evaluated by the simple observation of CdSe/ZnS PL with a couple of excitation wavelengths. Moreover, the differences observed for the temporal evolution of CdSe/ZnS PL (blue shifts and degradation) among the excitation wavelengths suggest that the photo-induced changes of chemical composition and surface ligands are responsible for blue shifts and degradation, respectively.     

Simultaneous determination of methylene blue and new methylene blue by slab optical waveguide spectroscopy and artificial neural networks

A slab optical waveguide (SOWG) has been used for study of adsorption of both methylene blue (MB) and new methylene blue (NMB) in liquid-solid interface. Adsorption characteristics of MB and NMB on both bare SOWG and silanized SOWG by octadecyltrichlorosilane (ODS) were compared. The simultaneous determinations of both MB and NMB were explored by flow injection SOWG spectrophotometric analysis and artificial neural networks (ANNs) for the first time. Concentrations of MB and NMB were estimated simultaneously with the ANNs. Results obtained with SOWG were compared with those got by conventional UV-visible spectrophotometry.