水溶液法制备CdSe和ZnSe纳米棒

用水溶液法直接合成了水溶性、发荧光的ZnSe和CdSe纳米棒。ZnSe纳米棒的直径约20～30nm,长度可达60～70nm;CdSe纳米棒的直径约30～60nm,长度可达150～450nm。用X射线衍射仪(XRD)、透射电镜(TEM)、高分辨透射电镜(HR-TEM)、荧光仪等仪器对纳米棒进行了表征。XRD和HRTEM的结果显示纳米棒具有立方结构,结晶度较高。讨论了纳米棒的形成机理以及pH对纳米棒发光强度的影响。合成的纳米棒在水溶液中至少稳定半年,表面被氨基和羧基化,在生物分析中具有广泛的应用前景。     

Green lasers based on CdSe/ZnSe nanostructures pumped by electron beams with energies below 10 keV

We have studied the output characteristics of pulsed electron-beam-pumped green lasers based on ZnSe-containing quantum-sized structures with thin (20 nm thick) external ZnMgSSe confinement layers. Room-temperature lasing has been observed for electron beam energies above 3.7 keV. At a beam energy of 8–9 keV, the minimum threshold beam current density was 0.4–0.5 A/cm². The maximum laser output pulse energy was 2 W at a pumping electron beam energy of ～5 kW.     

Bent Polytypic ZnSe and CdSe Nanowires Probed by Photoluminescence

Nanowires (NWs) have witnessed tremendous development over the past two decades owing to their varying potential applications. Semiconductor NWs often contain stacking faults due to the presence of coexisting phases, which frequently hampers their use. Herein, it is investigated how stacking faults affect the optical properties of bent ZnSe and CdSe NWs, which are synthesized using the vapor transport method. Polytypic zinc blende–wurtzite structures are produced for both these NWs by altering the growth conditions. The NWs are bent by the mechanical buckling of poly(dimethylsilioxane), and micro‐photoluminescence (PL) spectra were then collected for individual NWs with various bending strains (0–2%). The PL measurements show peak broadening and red shifts of the near‐band‐edge emission as the bending strain increases, indicating that the bandgap decreases with increasing the bending strain. Remarkably, the bandgap decrease is more significant for the polytypic NWs than for the single phase NWs. This work provides insights into flexible electronic devices of 1D nanostructures by engineering the polytypic structures.     

Facile synthesis and characterization of urchin-like CdSe nanostructures

CdSe nanostructures with urchin-like shape were successfully synthesized in water-in-oil (W/O) microemulsion. The phase structure, morphology, optical property, and specific surface area of the CdSe products were characterized. The X-ray powder diffraction pattern of the product showed that it is pure CdSe in zinc blende structure rather than thermodynamically favored wurtzite structure. It is found that numerous one-dimensional CdSe nanorods radiate from the center of the agglomerate to form urchin-like nanostructures and grow along the (111) crystal planes. The photoluminescence spectrum of the urchin-like nanostructures indicated that there is a blue-shift as compared with that of the bulk CdSe. Additionally, these interesting urchin-like nanostructures showed an increased specific surface area.     

CdSe/ZnSe量子点的制备及电化学发光性能

利用ZnSe半导体纳米材料晶体结构与CdSe相似、带隙更宽的特点,采用水热法合成了核-壳型CdSe/ZnSe量子点。结果表明：温度在70~160℃时,ZnSe壳逐渐包裹在CdSe核上,反应时间在0~4 h时,内壳在核上是均匀包裹的,当核壳摩尔比为1∶3时,CdSe/ZnSe QDs的电化学发光性能最强,其电化学发光强度是CdSe量子点的6倍,且发光信号稳定。     

Largely extended light-emission shift of ZnSe nanostructures with temperature

ZnSe nanowires and nanobelts with zinc blende structure have been synthesized. The morphology and the growth mechanisms of the ZnSe nanostructures will be discussed. From the photoluminescence (PL) of the ZnSe nanostructures, it is interesting to note that red color emission with only a single peak at the photon energy of 2 eV at room temperature is obtained while the typical bandgap transition energy of ZnSe is 2.7 eV. When the temperature is reduced to 150 K, the peak wavelength shifts to 2.3 eV with yellowish emission and then blue emission with the peak at 2.7 eV at temperature less than 50 K. The overall wavelength shift of 700 meV is obtained as compared to the conventional ZnSe of about 100 meV (i.e., sevenfold extension). The ZnSe nanostructures with enhanced wavelength shift can potentially function as visible light temperature-indicator. The color change from red to yellowish and then to blue is large enough for the nanostructures to be used for temperature-sensing applications. The details of PL spectra of ZnSe at various temperatures are studied from (i) the spectral profile, (ii) the half-width half-maximum, and (iii) the peak photon energy of each of the emission centers. The results show that the simplified configuration coordinate model can be used to describe the emission spectra, and the frequency of the local vibrational mode of the emission centers is determined.     

Synthesis of ZnSe quantum dots and ZnSe-ZnS core/shell nanostructures

Colloidal ZnSe nanocrystals were synthesized in hot mixtures of long-chain alkylamines, fatty acids, and alkylphosphines. It was possible to tune the size of nanocrystals by varying the reaction time. Transmission electron microscope images showed the presence of spherical ZnSe nanocrystals and X-ray diffraction pattern of ZnSe nanocrystals showed the existence of both the crystalline phase, namely, wurtzite and zinc blende. The ZnSe nanocrystals were then passivated with higher band gap ZnS; this lead to a 2.6-fold enhancement in the integrated photoluminescence intensity of ZnSe nanocrystals. We also synthesized the reverse type core/shell ZnS/ZnSe nanocrystals. These exhibited a significant red shift in the absorption edge after coating with a thin ZnSe shell.     

A case study: Te in ZnSe and Mn-doped ZnSe quantum dots

Photoluminescence (PL) behavior of ZnSe(1-y)Te(y) quantum dots is investigated by varying Te concentration as well as size. The striking effect of quantum confinement is the observation of isoelectronic center-related emission at room temperature in lieu of near-band-edge emission that dominates the optical scenario. ZnSe(0.99)Te(0.01) quantum dots were also doped by Mn(2+) ions. The Mn(2+) ion-related d-d transition is drastically suppressed by Te isoelectronic centers. Incorporation of Mn(2+) at substitutional sites in ZnSe(0.99)Te(0.01) quantum dots is also confirmed by the electron paramagnetic resonance measurements. Effect of Te isoelectronic impurity on the emission behavior is more pronounced than that of Mn(2+) ions. A subtle blueshift in the orange d-d transition is a sign of a decrease in crystal field strength. PL and photoluminescence excitation measurements on Zn(1-x)Se(0.99)Te(0.01)Mn(x) quantum dots indicate that the transition probability from the lowest unoccupied molecular orbital to Te levels is substantially larger than that to Mn(2+) d-d levels.     

Redistribution of localised excitons in CdSe/ZnSe quantum dot structures

Population processes and recombination mechanisms of excitons localised in CdSe/ZnSe quantum dot structures are investigated. The photoluminescence (PL) properties are governed by lateral energy transfer within a dense ensemble of quantum dots, which differ in size and Cd concentration, providing for a complex potential landscape with localisation sites of widely varying depth for excitons. At low temperatures, lateral transfer by tunnelling leads to a mobility edge at 2.561 eV. Thermally activated escape and recapture of excitons cause a strong redshift of the PL maximum and the mobility edge.     

A rational elemental-directed alcohol-thermal route to CdSe nanostructures for thin film solar cells

We have reported an alcohol-thermal method to in-situ synthesis of Cadmium Selenide (CdSe) nanocrystals/thin films on Cd/indium-doped tin oxide (ITO) substrates through a direct reaction of Se and Cd. In the synthetic system, ligands and surfactants are not introduced, and concentration of reaction precursors is not high, thus not only it is a very economic and environmental-friendly route, but also the CdSe film without any impurities is obtained. The Cd deposited on ITO substrates by magnetron sputtering acted as dual roles: reactant source and hard template for the final product. The microstructure is analyzed by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). Poly(3-hexylthiophene) (P3HT) is deposited on CdSe film to fabricate a hybrid thin film solar cell device with ITO/CdSe/P3HT/Al structure to demonstrate solar light to electrical energy conversion.     

Investigation of intrinsic defects and their distribution in CdSe/ZnSe quantum dot structures

The intrinsic defects and their distribution in CdSe/ZnSe self-assembled quantum dot heterostructures grown under variation of VI/II group beam pressure ratio are investigated by luminescent and high-resolution X-ray diffraction methods. In all samples the self-activated emission connected with donor-acceptor pairs V_Zn–D is found. Analysis of excitation spectra of this band shows that vacancy related defects are mainly localised in ZnCdSe wetting layer. It is found that increase of Se beam pressure results in: (i) the increase of the number of metal vacancy related defects and their appearance on nanoisland interface; (ii) enhancement of Cd/Zn interdiffusion process; (iii) the decrease of Cd content in nanoislands and suppression of nanoisland formation. It is proposed that observed transformation of nanoisland emission band is mainly caused by enhancement of interdiffusion process.     

Synthesis and characterization of metal selenide (ZnSe, CdSe, HgSe) nanoparticles

Thermolysis of [M(SeCH2CH2CH2NMe2)2] (M = Zn, Cd, Hg), prepared by the reactions of sodium salt of 3-(N,N-dimethylamino)propaneselenolate with metal acetates, afforded metal selenides (MSe). The metal selenides were characterized by XRD, EDAX, SEM, AFM, and TEM techniques. Nanoparticles of HgSe were prepared by pyrolysis in a quartz boat, solvothermal, and sonochemical methods. EDAX showed 1:1 Hg/Se ratio, while XRD and SAED patterns confirmed the formation of cubic HgSe. These particles are spherical in nature with an average diameter of 15 nm (from TEM).     

Raman spectra and photoluminescence properties of In-doped ZnO nanostructures

In-doped ZnO nanostructures with four different morphologies, which are nanotetrapods, nanocombs, nanowires, and nanodisks, have been synthesized on silicon substrates by a simple thermal evaporation method. The XRD patterns show the In-doped ZnO nanostructures are all with the hexagonal wurtzite structure, and a slight difference in lattice parameters had been detected among the samples with various morphologies. The Raman spectra demonstrate that the vibrational mode of 2LA, which is very weak in undoped ZnO, was strongly enhanced with indium ion doping into ZnO structures. The photoluminescence (PL) measurements indicate that the nanodisks have a relative strong ultraviolet (UV) emission than other three kinds of samples.     

Peculiarities of the thermal activation of carriers in CdSe/ZnSe QD structures

The results of experimental and theoretical investigations of thermal quenching of quantum dot (QD) photoluminescence (PL) in CdSe/ZnSe heterostructures are presented. It is found that at low temperatures, when carriers are strongly localized in QDs, QD PL intensity depends linearly on excitation power, but at higher temperatures, when carriers are thermally excited to the wetting layer, this dependence becomes superlinear. The activation energy of thermal quenching of QD PL intensity is found to be smaller than the sum of QD electron and hole potential depths. It is shown that these facts are explained satisfactorily by the model of independent electron and hole capture (escape) in QDs.     

Highly luminescent CdSe/ZnSe core-shell quantum dots of one-pot preparation in octadecene

CdSe/ZnSe core-shell quantum dots were synthesized using a new one-pot procedure where the core was prepared in octadecene. A ZnSe shell around a CdSe nanoparticle was formed by the reaction of selenium-richness on the surfaces of CdSe nanoparticles with Zn2+ from the injected zinc stearate precursor. The optical properties, luminescence kinetics, and the effect of shell thickness of as-prepared QDs were studied, which verifies the high quality of the resulting QDs. The new approach is effective not only for preparing core/shell QDs, but also for reducing the complexity of synthesis, toxicity, and reagent cost.     

Synthesis and Ex situ doping of ZnTe and ZnSe nanostructures with extreme aspect ratios

We report synthesis windows for growth of millimeter-long ZnTe nanoribbons and ZnSe nanowires using vapor transport. By tuning the local conditions at the growth substrate, high aspect ratio nanostructures can be synthesized. A Cu-ion immersion doping method was applied, producing strongly p-type conduction in ZnTe and ionic conduction in ZnSe. These extreme aspect ratio wide-bandgap semiconductors have great potential for high density nanostructured optoelectronic circuits.      

Lasing in submonolayer CdSe structures in a ZnSe matrix without external optical confinement

It is shown that in order to achieve lasing in structures with CdSe submonolayers inserted in a ZnSe matrix, no additional optical confinement of the active region using thick wide-gap layers is required. The high oscillator strength of the excitons trapped at CdSe islands modulates the permittivity and thus produces a natural exciton-induced waveguiding effect. Pis’ma Zh. Tekh. Fiz. 23, 33–38 (January 12, 1997)