A separation mechanism of photogenerated charges and magnetic properties for BiFeO3 microspheres synthesized by a facile hydrothermal method

BiFeO(3) (BFO) microspheres were synthesized by a facile hydrothermal method. The optical absorption spectrum indicates that on site Fe(3+) crystal-field transitions and the charge transfer excitations can be observed. Magnetic measurements show a spin-glass behavior and room temperature weak ferromagnetism. The surface photovoltage spectroscopy of the BFO shows two response peaks centered at about 370 and 400 nm, respectively. Under an ambient atmosphere, the maximum surface photovoltage of the BFO reaches 180 μV with the bias (+2 V) and is three times larger than that with zero bias. It is found that the surface photovoltage response intensity increases with an increase in applied bias, regardless of positive or negative bias. It is suggested that the surface photovoltaic properties are related to both the depolarization field owing to ferroelectric polarization and the build-in electric field due to the Schottky barrier. The micro-process and the physical mechanism of the separation of photogenerated charges for BFO are fully explained.     

Graphene quantum dots assisted photovoltage and efficiency enhancement in CdSe quantum dot sensitized solar cells

CdSe quantum dot sensitized solar cells(QDSCs) modified with graphene quantum dots(GQDs) have been successfully achieved in this work for the first time. Satisfactorily, the optimized photovoltage(Voc) of the modified QDSCs was approximately 0.04 V higher than that of plain CdSe QDSCs, consequently improving the photovoltaic performance of the resulting QDSCs. Served as a novel coating on the CdSe QD sensitized photoanode, GQDs played a vital role in improving Vocdue to the suppressed charge recombination which has been confirmed by electron impedance spectroscopy as well as transient photovoltage decay measurements. Moreover, different adsorption sequences, concentration and deposition time of GQDs have also been systematically investigated to boost the power conversion efficiency(PCE) of CdSe QDSCs. After the coating of CdSe with GQDs, the resulting champion CdSe QDSCs exhibited an improved PCE of 6.59% under AM 1.5G full one sun illumination.     

Surface Chemistry Studies of Quantum Dots (QDs) Modified with Surfactants

Since luminescent CdSe quantum dots (QDs) have shown great potential in biological labeling, the surface chemistry behavior of QDs at interfaces is of great research interest. In the present study, CdSe QDs with green luminescence were modified with hydrophobic chains of varying lengths [from C6 to C18]. These modified QDs can be utilized to form stable monolayers at the air/water interface. Surface pressure-area isotherms of modified QDs have been measured and limiting molecular areas have also been extrapolated in order to analyze the size of the QDs. UV absorption spectra of modified QDs at various surface pressures were also determined. Surface chemistry, as well as the topographic properties, of modified QDs in Langmuir and L-B films was discussed.     

硒化镉量子点膜的拉曼光谱及拉曼成像分析

研究了CdSe量子点膜的Raman光谱,发现CdSe量子点的横模(TO)振动活性较强,表面模(SO)、纵模(LO)振动不明显。比较了量子点、氧化三辛基膦及十六胺的Raman光谱,证明量子点表面大部分区域被十六胺及二辛胺修饰。在此基础上,对量子点膜的TO模振动及C-H弯曲振动峰进行了Raman成像分析,并与明场图像进行了对比,表明拉曼成像信号对量子点膜的表面变化非常敏感。     

Synthesis of Mn-doped zinc blende CdSe nanocrystals for quantum dot-sensitized solar cells

Mn-doped CdSe quantum dots (QDs) with a zinc blende structure were synthesized via a phosphine-free method in octadecene (ODE) and oleic acid. The structure, size, morphology, and optical property of the QDs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible absorption spectra (UV–Vis), respectively. The QDs were assembled onto a microporous TiO₂ photoanode by an ex situ ligand exchange route. Quantum dot-sensitized solar cells (QDSCs) based on the above-synthesized QDs and polysulfide electrolytes were fabricated. The photovoltaic performance and impedance of the CdSe and Mn-doped CdSe QDSCs were further investigated. An improvement in efficiency to 1.84 % was achieved as compared with 0.94 % for the QDSCs based on the pure CdSe QDs. The improvement was ascribed to the existence of long-lived high-energy doping levels on the large-sized Mn-doped CdSe QDs, which provides a significant driving force for faster charge separation and electron transfer.     

CdSe quantum dot-dispersed DOBAMBC: an electro-optical study

Cadmium selenide quantum dot (CdSe QD) has been used as a dopant in ferroelectric liquid crystal (FLC) 2-methylbutyl 4-(4-decyloxybenzylideneamino) cinnamate (DOBAMBC). Effect of CdSe QD in DOBAMBC on its different electro-optical (E-O) properties has been studied in the SmC* phase. The optical micrographs recorded for the pure and composite material are showing good dispersion of QDs in the FLC matrix. Micrographs of unaligned sample cell revealed that CdSe QDs induce homeotropic alignment of FLC molecules. An appreciable change in the value of E-O parameters like tilt angle, spontaneous polarisation and response time with shifting of SmA–SmC* phase transition temperature has been observed for CdSe QD–DOBAMBC composite. The observed properties of composite system have been discussed on the basis of surface properties of QDs in FLC system.     

偏振光作用下金红石型TiO2单晶(001)面的表面光电压谱研究

TiO2是一种优异的光电功能材料,被广泛用于有机污染物光降解及太阳能光电转换[1～3].近年来的研究表明,表面原子排布对TiO2光电效能有决定性的影响.如Lowckamp[3]的研究表明,TiO2的(101)晶面与其它晶面相比具有高的光化学还原Ag+的能力.本文结合偏振光技术与表面光电压谱技术对金红石型TiO2单晶(001)面的光伏响应特性进行了研究,通过对TiO2不同晶面的电子跃迁形式的区分及其对偏振光的不同响应,揭示了表面原子排布与TiO2光电性质之间的关系,实现了对材料功能特性的调控.     

Plate, wire, mesh, microsphere, and microtube composed of sodium titanate nanotubes on a titanium metal template

Sodium titanate nanotube/titanium metal composites were synthesized by hydrothermal treatment of titanium metals with various morphologies such as plate, wire, mesh, microsphere, and microtube at 160 degrees C in aqueous NaOH solution and by the subsequent fixation treatment by calcination at 300 degrees C. The surface of the composite was covered with sodium titanate nanotubes with a diameter of approximately 7 nm, and the core part of the composite was titanium metal phase. The raw titanium metal acts as a template or a morphology-directing agent of micrometer size or more to arrange the nanotubes as well as a titanium source for the formation of nanotubes. The concentration of titanium species increases in the reaction solution as the dissolution of titanium metal is accelerated by the reaction between titanium and OH-. Furthermore, with an increase in concentration of titanium species in the reaction solution, the titanium species are re-precipitated as sodium titanate nanotubes onto the titanium metal. Titanium metal with a large surface area and volume can form sodium titanate nanotubes on the surface of the titanium metal, though titanium metal with a small volume and surface area tends to dissolve with the hydrothermal treatment. Even in the synthesis using titanium metal with a small volume and surface area, sodium titanate nanotubes are formed and cover the surface of the titanium metal by adding another titanium metal as a source of titanium species in the reaction solution.     

Functionalized CdSe quantum dots as selective silver ion chemodosimeter

CdSe quantum dots (QDs) have been prepared and modified with mercaptoacetic acid. They are water-soluble and biocompatible. To improve their fluorescence intensity and stability in water solution, bovine serum albumin (BSA) was absorbed onto their surface. Based on the quench of fluorescence signals of the functionalized CdSe QDs in the 543 nm wavelength and enhancement of them in the 570-700 nm wavelength range by Ag(I) ions at pH 5.0, a simple, rapid and specific method for Ag(I) determination was proposed. In comparison with single organic fluorophores, these nanoparticles are brighter, more stable against photobleaching, and do not suffer from blinking. Under the optimum conditions, the response is linearly proportional to the concentration of Ag(I) between 4.0 x 10(-7) and 1.5 x 10(-5) mol L(-1), and the limit of detection is 7.0 x 10(-8) mol L(-1). The mechanism of reaction is also discussed.     

TiO2负载型催化剂及光催化还原CO2反应的表面光电压谱研究

半导体TiO₂作为光催化剂,已被广泛应用于光催化废水处理及光催化储能^[1,2]等方面的研究.人们不断开发高活性的新型光催化剂并对其反应机理进行了探索性研究^[3],希望通过表面负载Pd、Ru、Pt或Rh等贵金属的小岛式颗粒以传递光生电子(或光生空穴).     

功能化多壁碳纳米管的光电性质

表面光电压谱;循环伏安;金刚石薄膜电极;功能化多壁碳纳米管的光电性质     

Nanoscale connectivity in a TiO2/CdSe quantum dots/functionalized graphene oxide nanosheets/Au nanoparticles composite for enhanced photoelectrochemical solar cell performance

Electron transfer dynamics in a photoactive coating made of CdSe quantum dots (QDs) and Au nanoparticles (NPs) tethered to a framework of ionic liquid functionalized graphene oxide (FGO) nanosheets and mesoporous titania (TiO(2)) was studied. High resolution transmission electron microscopy analyses on TiO(2)/CdSe/FGO/Au not only revealed the linker mediated binding of CdSe QDs with TiO(2) but also, surprisingly, revealed a nanoscale connectivity between CdSe QDs, Au NPs and TiO(2) with FGO nanosheets, achieved by a simple solution processing method. Time resolved fluorescence decay experiments coupled with the systematic quenching of CdSe emission by Au NPs or FGO nanosheets or by a combination of the latter two provide concrete evidences favoring the most likely pathway of ultrafast decay of excited CdSe in the composite to be a relay mechanism. A balance between energetics and kinetics of the system is realized by alignment of conduction band edges, whereby, CdSe QDs inject photogenerated electrons into the conduction band of TiO(2), from where, electrons are promptly transferred to FGO nanosheets and then through Au NPs to the current collector. Conductive-atomic force microscopy also provided a direct correlation between the local nanostructure and the enhanced ability of composite to conduct electrons. Point contact I-V measurements and average photoconductivity results demonstrated the current distribution as well as the population of conducting domains to be uniform across the TiO(2)/CdSe/FGO/Au composite, thus validating the higher photocurrent generation. A six-fold enhancement in photocurrent and a 100 mV increment in photovoltage combined with an incident photon to current conversion efficiency of 27%, achieved in the composite, compared to the inferior performance of the TiO(2)/CdSe/Au composite imply that FGO nanosheets and Au NPs work in tandem to promote charge separation and furnish less impeded pathways for electron transfer and transport. Such a hierarchical rapid electron transfer model can be adapted to other nanostructures as well, as they can favorably impact photoelectrochemical performance.     

3-巯基丙酸修饰的CdSe/ZnS量子点的合成及测定牛血清白蛋白的研究

以3-巯基丙酸作为修饰剂,在水溶液中合成了稳定的CdSe/ZnS量子点(QDs),透射电镜观察所合成量子点的形貌近似球形,粒径约为25 nm.吸收光谱与荧光光谱的研究表明,CdSe QDs在410 nm处有最大吸收峰,而CdSe/ZnS QDs的最大吸收峰在470 nm处,CdSe/ZnS QDs的荧光强度是CdSe QDs的11倍.考察了缓冲溶液的体积、pH值、反应温度、反应时间对体系荧光的影响.在最佳实验条件下,体系的荧光强度与BSA的浓度呈线性关系,线性响应范围为0.746×10-7～4.48×10-7 mol/L,检出限为3.846×10-10 mol/L.并且CdSe/ZnS QDs荧光强度基本保持稳定,可达两个多月.该方法应用于合成样品的测定,结果满意.     

Uncovering the role of the ZnS treatment in the performance of quantum dot sensitized solar cells

Among the third-generation photovoltaic devices, much attention is being paid to the so-called Quantum Dot sensitized Solar Cells (QDSCs). The currently poor performance of QDSCs seems to be efficiently patched by the ZnS treatment, increasing the output parameters of the devices, albeit its function remains rather unclear. Here new insights into the role of the ZnS layer on the QDSC performance are provided, revealing simultaneously the most active recombination pathways. Optical and AFM characterization confirms that the ZnS deposit covers, at least partially, both the TiO(2) nanoparticles and the QDs (CdSe). Photoanodes submitted to the ZnS treatment before and/or after the introduction of colloidal CdSe QDs were studied by electrochemical impedance spectroscopy, cyclic voltammetry and photocurrent experiments. The corresponding results prove that the passivation of the CdSe QDs rather than the blockage of the TiO(2) surface is the main factor leading to the efficiency improvement. In addition, a study of the ultrafast carrier dynamics by means of the Lens-Free Heterodyne Detection Transient Grating technique indicates that the ZnS shell also increases the rate of electron transfer. The dual role of the ZnS layer should be kept in mind in the quest for new modifiers for enhancing the performance of QDSCs.     

Effect of CdSe quantum dots doping on the switching time,localised electric field and dielectric parameters of ferroelectric liquid crystal

A systematic study highlighting the effect of cadmium selenide quantum dots (CdSe QDs) with varying concentrations of 0.05, 0.10 and 1.0 wt% doping on the electrooptical and dielectric parameters of ferroelectric liquid crystal (FLC) is presented. No considerable change is observed in phase transition temperature and tilt angle with CdSe QDs doping at lower and higher dopant level. Substantial enhancement of localised electric field at higher doping level (1.0 wt%) of CdSe QDs manifested the ≈48% reduction in the switching response of FLC nanocolloids at 30°C. Reduction in the spontaneous polarisation, dielectric constant and absorption strength could be attributed to the antiparallel correlation among dopant and matrix molecules, ion capturing in the capping additive layer and enhancement of the rotational viscosity of the nanocolloids, respectively. Goldstone mode relaxation frequency is found to be decreased with doping up to 0.10 wt% concentration and showed reverse effect at higher QDs concentration. QDs doping effect on the photoluminescence intensity is also discussed.     

Observation of enhanced energy transfer in individual quantum dot-oligophenylene vinylene nanostructures

The temporal and spectral properties of luminescence from individual CdSe quantum dot-oligophenylene vinylene nanostructures (single quantum dots with conjugated organic ligands coordinated to the surface) are profoundly modified relative to blended films of the same components. These kinds of composite quantum dot-conjugated organic systems have attracted significant interest as a way to improve efficiency in photovoltaic device applications. By direct functionalization of the dot surface with the conjugated organic ligands, we realize a significant enhancement in energy transfer and luminescence stability.     

A novel fluorescent assay for edaravone with aqueous functional CdSe quantum dots

Aqueous thiol-capped CdSe QDs with a narrow, symmetric emission were prepared under a low temperature. Based on the fluorescence enhancement of thiol-stabilized CdSe quantum dots (QDs) caused by edaravone, a simple, rapid and specific quantitative method was proposed to the edaravone determination. The concentration dependence of fluorescence intensity followed the binding of edaravone to surface of the thiol-capped CdSe QDs was effectively described by a modified Langmuir-type binding isotherm. Factors affecting the fluorescence detection for edaravone with thiol-stabilized CdSe QDs were studied, such as the effect of pH, reaction time, the concentration of CdSe QDs and so on. Under the optimal conditions, the calibration plot of C/(I − I₀) with concentration of edaravone was linear in the range of (1.45–17.42) μg/mL (0.008–0.1 μmol/L) with correlation coefficient of 0.998. The limit of detection (LOD) (3σ/κ) was 0.15 μg/mL (0.0009 μmol/mL). Possible interaction mechanism was discussed.     

CuInSe2/氰桥混配物复合修饰光电极的制备及其光电性质

利用电沉积法在氰桥混配物预修饰的玻璃碳电极上再沉积CuInSe2半导体材料,制备了一种复合型修饰光电极(Eu-Fe-Mo/CuInSe2)。以含Cu2+、In3+、SeO23-及柠檬酸钠的酸性水溶液为电镀液,通过优化寻找到电镀液中最佳的Cu∶In∶Se料液比例,用恒电位电沉积法可以制备出具有良好光电效应的复合型修饰光电极。用SEM、EDS技术对复合修饰光电极的表面形貌及其修饰材料的元素组成进行了表征;以60 W的普通日光型白炽灯为光源,采用开路电压和计时安培法研究了该复合修饰光电极的光电性质。测得该光电极的响应光电压大于30 mV,响应光电流密度大于8.9×10-6A/cm2。实验结果表明,该复合修饰光电极呈现典型p型半导体的光电性质。     

Characterization of CdSe quantum dots with bidentate ligands by capillary electrophoresis

The CdSe quantum dots (QDs) with bidentate ligands: a-diimine (NN) and dihydrolipoic acid (DHLA) were synthesized and characterized by UV-Vis, particle size and capillary electrophoretic techniques. Two systems were analyzed: CdSe with one ligand (CdSe/ligand) and CdSe with two different ligands (CdSe//ligand1/ligand2), where ligand = α-diimine or DHLA. Hydrodynamic features of functionalized QDs were characterized by zone capillary electrophoretic (CZE), and particle size techniques and these methods were consistent. It was established that CZE, micellar (MEKC) and microemulsion (MEEKC) modes were suitable for separating charged CdSe QDs and that no peaks were obtained for QDs passivated with electrically neutral ligands. For CdSe QDs with neutral (NN) ligands, a preconcentration method with the use of a micellar plug was introduced for visualizing these QDs. A sharp peak representing neutral QDs was obtained within the zone of micellar plug of a non-ionic surfactant, Here, a ligand character used for CdSe modification and the type of the electrophoretic method applied were the determining factors for the QDs peak visualization. Moreover, examples of visualization of charged and neutral QDs on the same run were presented, and for this purpose, dual mechanism (separation/preconcentration) was proposed.      

The Application of CdSe Quantum Dots with Multicolor Emission as Fluorescent Probes for Cell Labeling

Herein, highly luminescent CdSe quantum dots (QDs) with emissions from the blue to the red region of visible light were synthesized by using a simple method. The emission range of the CdSe QDs could be tuned from λ=503 to 606 nm by controlling the size of the CdSe QDs. Two amino acids, L ‐tryptophan (L ‐Trp) and L ‐arginine (L ‐Arg), were used as coating agents. The quantum yield (QY) of CdSe QDs (green color) with an optimized thickness could reach up to 52 %. The structures and compositions of QDs were examined by using X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Optical properties were studied by using UV/Vis and photoluminescence (PL) spectroscopy and a comparison was made between uncoated and coated CdSe QDs. The amino acid‐modified β‐cyclodextrin (CD)‐coated CdSe QDs presented lower cytotoxicity to cells for 48 h. Furthermore, amino acid‐modified β‐CD‐coated green CdSe QDs in HepG2 cells were assessed by using confocal laser scanning fluorescence microscopy. The results showed that amino acid‐modified β‐CD‐coated green CdSe QDs could enter tumor cells efficiently and indicated that biomolecule‐coated QDs could be used as a potential fluorescent probe.