核/壳结构的ZnS:Mn/SiO_2纳米粒子的制备及发光性质研究

采用溶剂热法制备了Mn离子掺杂的ZnS纳米粒子(ZnS∶Mn),然后利用正硅酸乙酯(TEOS)的水解反应对其进行了不同厚度的SiO2无机壳层包覆。采用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)及荧光发射光谱(PL)对样品的结构及光学性质进行了表征和研究。包覆SiO2壳层后,粒子的粒径明显增大并且在ZnS∶Mn纳米粒子表面可以观察到明显的SiO2壳层。XPS测试印证了ZnS∶Mn/SiO2的核壳结构。随着SiO2壳层的增厚,ZnS∶Mn/SiO2的Mn离子的发光先增强后减弱,这是因为SiO2壳层同时具有表面修饰和降低发光中心浓度这两种相反的作用。当壳层厚度(壳与核的物质的量的比)达到5时,发光效果达到最好,其强度达到未包覆样品的7.5倍。     

核壳结构CdS/ZnS纳米微粒的制备与光学特性

用微乳液法制备CdS纳米微粒 ,以ZnS对其进行表面修饰 ,得到具有核壳结构的CdS/ZnS纳米微粒 .采用X射线衍射 (XRD)、透射电镜 (TEM )表征其结构、粒度和形貌 ,紫外 可见吸收光谱 (UV)、光致发光光谱(PL)表征其光学特性 .制得的CdS近似呈球形 ,直径为 3.3nm ;以XRD和UV证实了CdS/ZnS核壳结构的实现 .研究了不同ZnS壳层厚度对CdS纳米微粒光学性能的影响 ,UV谱表明随着壳层厚度的增加纳米微粒的吸收带边有轻微的红移 ,同时短波吸收增强 ;PL谱表明壳层ZnS的包覆可减少CdS纳米微粒的表面缺陷 ,带边直接复合发光的几率增大 ,具有合适的壳层厚度时发光效率大大提高 .     

单核/双壳结构CdSe/CdS/ZnS纳米晶的合成与发光性质

以巯基乙酸为稳定剂,在水溶液中合成了单核/双壳结构的CdSe/CdS/ZnS纳米晶。在内核CdSe和外壳ZnS之间的内壳CdS作为晶格匹配调节层,能够很好的改善核/壳界面处的性能,而且,最外层ZnS能够最大程度地使激子受限。用TEM和XPS对纳米晶进行了表征,并且用光致发光光谱和吸收光谱对不同核壳结构的纳米晶的发光性能进行了比较,结果表明单核/双壳结构的纳米晶具有更加优异的发光特性。     

真空热蒸发制备CdS/ZnS核/壳异质结纳米线

将传统的真空热蒸发镀膜实验加以改进,先以催化剂辅助蒸发制备出CdS纳米线,再将其作为模板,以ZnS为蒸发源物质,二次蒸发包覆ZnS层,成功制备出大量的CdS/ZnS核/壳异质结纳米线.经X射线衍射、X射线能量色散谱、透射电镜分析表明,所得CdS/ZnS异质结纳米线的核心部分为CdS单晶纳米线,外层为ZnS多晶层.本文的实验方法简便易行,所得纳米结构在光电纳米器件领域有一定应用前景.     

ZnSe(ZnS)纳米晶与MEH-PPV的共掺有机电致发光器件

采用水相法合成核壳结构ZnSe/ZnS 纳米晶,经X射线衍射(XRD)分析和透射电子显微镜(TEM)表征,证实所制备的样品为立方晶型闪锌矿结构ZnSe/ZnS量子点。按照一定的质量比将ZnSe/ZnS 纳米晶和有机聚合物MEH-PPV(poly ) 共掺并将其作为发光层,分别制备单层和多层有机电致发光器件,结构为ITO/MEH-PPV∶ZnSe(ZnS)(50 nm)/Al和 ITO/PEDOT∶PSS(70 nm)/ MEH-PPV∶ZnSe(ZnS)(50 nm)/BCP(15 nm)/Alq₃(12 nm) /LiF(0.5 nm)/Al。实验结果表明,多层发光器件的发光特性与单层器件不同,工作电压的增大使其发光峰发生了明显的蓝移。     

核-壳结构的ZnS:Mn纳米粒子的荧光增强

采用反胶束方法制备了ZnS :Mn纳米粒子并对其进行了ZnS壳层修饰 ,采用发射光谱和激发光谱对其光学性质进行了研究。与未包覆的ZnS:Mn纳米粒子相比 ,核 壳结构的ZnS :Mn纳米粒子来自于Mn2 离子的 5 80nm的发光增强了数倍 ,归因于ZnS壳增加了Mn2 离子到纳米颗粒表面的距离 ,减弱了Mn2 离子向表面猝灭中心的传递。样品制备后 ,核 壳结构的ZnS :Mn纳米粒子在 5 80nm的发光随时间略有增强 ,激发光谱的位置未发生明显变化 ,而未包覆的ZnS:Mn纳米粒子在 5 80nm的发光显著增强 ,同时自激活发光减弱 ,激发光谱明显发生红移 ,说明未包覆的ZnS :Mn纳米粒子的尺寸随时间增大 ,而核 壳结构的ZnS :Mn纳米粒子尺寸基本不变。     

核-壳结构ZnS∶Tb/CdS纳米晶的电致发光

利用微乳液方法合成出粒径为4 nm的核-壳结构ZnS∶Tb/CdS纳米晶。用XRD、TEM及荧光光谱等手段对合成的纳米晶的结构、形态和光学特性分别进行了表征。将ZnS∶Tb/CdS纳米晶制作成有机-无机杂化结构电致发光器件,其结构为ITO/poly(3,4-ethylene d ioxythiophene)∶poly(styrene sulfonate)(PEDOT-PSS)(70 nm)/poly(vinylcobarzale)(PVK)(100 nm)/ZnS∶Tb/CdS纳米晶(120 nm)/2,9-d im ethyl-4,7-d iphenyl-1,10-phenanthroline(BCP)(30 nm)/L iF(1.0 nm)/A l(100 nm)。当驱动电压为13 V时,可以测到Tb3+离子的两个特征峰。在电致发光光谱中未测到聚合物PVK的发光,说明电子和空穴是在纳米晶层上复合的。当驱动电压为25 V时,得到器件的最大亮度为19 cd/m2。     

与掺杂浓度相关的ZnS∶Mn纳米粒子的发光性质

采用溶胶法制备了Mn掺杂的ZnS纳米粒子,探讨了掺杂离子浓度对ZnS∶Mn纳米粒子的晶体结构和发光性质的影响。通过X射线衍射（XRD）对样品的结构进行了表征,结果表明：所制备的ZnS∶Mn纳米粒子为立方闪锌矿结构,其在Mn离子的掺杂浓度达到6%时不发生分相,但随着掺杂浓度的增加,纳米粒子的平均粒径会减小。光致发光光谱和荧光光谱的结果表明：通过改变掺杂离子的浓度可实现对ZnS∶Mn纳米粒子590 nm附近荧光发射波长的调节。此外,研究了温度对纳米粒子形貌和发光性质的影响。高分辨透射电子显微镜（HRTEM）观察发现,经过50℃陈化1 h后的ZnS∶Mn样品的平均粒径增大约为20 nm,且加热陈化有利于ZnS∶Mn纳米粒子中Mn2＋在590 nm处产生荧光。     

ZnS:Mn2+/聚苯乙烯核壳及ZnS:Mn2+中空球的制备和光谱性质

采用超声化学沉积法制备了ZnS:Mn2+/聚苯乙烯核壳结构和ZnS:Mn2+空心球.产物分别用透射电镜、X射线衍射仪和光致发光谱进行了表征.透射电镜结果表明,在聚苯乙烯胶体微球表面覆盖了平均尺寸为9nm的ZnS:Mn2+纳米颗粒,X射线衍射结果进一步验证了这个结论.将核壳粒子在500℃灼烧除去PS核后,可以得到空心的ZnS:Mn2+微球,Mn2+的发射谱的峰位在540nm,与体相材料相比,蓝移了45nm,这可能是由于壳层结构引起Mn-O八面体畸变,进而导致能带结构变化引起的.     

核-壳结构的ZnS∶Cu/ZnS纳米粒子的制备及发光性质研究

制备了核-壳结构的ZnS∶Cu/ZnS纳米粒子以及普通的没有壳的Cu2 掺杂的ZnS纳米粒子,研究了ZnS无机壳层对ZnS∶Cu纳米粒子发光性质的影响。透射电子显微镜、激发光谱和发射光谱的研究表明,后加入的Zn2 离子在已经形成的ZnS核表面生长,形成ZnS壳层;而适当厚度的ZnS壳层可以钝化粒子表面,减少无辐射复合中心的数目,抑制表面态对发光的不利影响,提高ZnS∶Cu纳米粒子中Cu2 离子在450 nm左右的发光强度。     

Luminescence enhancement of Mn doped ZnS nanocrystals passivated with zinc hydroxide

Mn-doped ZnS nanocrystals prepared by solvothermal method have been successfully coated with different thicknesses of Zn(OH)₂ shells through precipitation reaction. The impact of Zn(OH)₂ shells on luminescent properties of the ZnS:Mn nanocrystals was investigated. X-ray diffraction (XRD) measurements showed that the ZnS:Mn nanocrystals have cubic zinc blende structure. The morphology of nanocrystals is spherical shape measured by transmission electron microscopy (TEM). ZnS:Mn/Zn(OH)₂ core/shell nanocrystals exhibited much improved luminescent properties than those of unpassivated ZnS:Mn nanocrystals. The luminescence enhancement was observed with the Zn(OH)₂ shell thickening by photoluminescence (PL) spectra at room temperature and the luminescence lifetime of transition from ⁴T₁ to ⁶A₁ of Mn²⁺ ions was also prolonged. This result was led by the effective, robust passivation of ZnS surface states by the Zn(OH)₂ shells, which consequently suppressed nonradiative recombination transitions.     

Synthesis and Characterization of CdS/CISe Quantum Dots with Core–Shell Structure

Quantum dots have received great interest due to their excellent optoelectronic properties. However, the surface defects of quantum dots affect the carrier transport and ultimately reduce the photovoltaic efficiency. In this paper, a core–shell quantum dot by hot-injection method is prepared to grow a narrow-band semiconductor layer (CuInSe₂ (CISe) quantumdot) on the surface of a broad-band core material (cadmium sulfide (CdS) nanocrystal). The composition, structure, optical properties, and decay lifetime of CdS/CISe core–shells are investigated in more detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), photoluminescence (PL), UV–vis spectrophotometry, and fluorescence spectroscopy. The CdS/CISe core–shell structure has a broadened absorption range and still shows CISe-related quantum effects. The increased size of the core–shell and the smaller specific surface area of the CISe shell layer lead to a lower carrier complexation chance, which improves the carrier lifetime.     

CdS/ZnS core–shell nanoparticles in arachidic acid LB films

Core–shell CdS/ZnS nanoparticles in arachidic acid film were prepared through a novel Langmuir–Blodgett (LB) approach. Post-deposition treatment of the precursor LB multilayers of cadmium arachidate with H₂S gas followed by intercalation of Zn²⁺ ions and further sulfidation result in the formation of CdS/ZnS nanoparticles in the LB film. The formation of these nanoparticles and resulting changes in layered structures were studied by FTIR and X-ray reflection measurements. The optical properties were studied using UV–vis absorption and photoluminescence spectroscopy. A red-shift in the absorption spectrum and enhancement of CdS excitonic emission together with reduction of surface states emission suggest that after the intercalation step, a thin layer of ZnS surrounds the CdS nanoparticles, thus forming a core–shell structure. Subsequent to the second sulfidation, a further red-shift in absorption suggests the formation of a thicker ZnS coating on CdS. Electron diffraction of CdS nanoparticles coated with thicker ZnS showed the diffraction patterns of only ZnS, as expected for core–shell structures.     

Synthesis of robust water-soluble ZnS:Mn/SiO2 core/shell nanoparticles

Water-soluble Mn doped ZnS (ZnS:Mn) nanocrystals synthesized by using 3-mercaptopropionic acid (MPA) as stabilizer were homogeneously coated with a dense silica shell through a multi-step procedure. First, 3-mercaptopropyl triethoxy silane (MPS) was used to replace MPA on the particle surface to form a vitreophilic layer for further silica deposition under optimal experimental conditions. Then a two-step silica deposition was performed to form the final water-soluble ZnS:Mn/SiO₂ core/shell nanoparticles. The as-prepared core/shell nanoparticles show little change in fluorescence intensity in a wide range of pH value.     

Mechanoluminescence and thermoluminescence of Mn doped ZnS nanocrystals

This paper reports the synthesis of ZnS:Mn nanocrystals by the chemical route in which mercaptoethanol was used as the capping agent. The particle size of such nanocrystals was measured using XRD and TEM patterns and was found to be in between 3and 5 nm. It was found that the peak position of TL glow curve and the TL intensity of ZnS:Mn nanoparticles increases as the particle size is decreased. The isothermal decay technique is used to determine the trap-depth. The stability of the charge carriers in the traps increase with the decrease in size of the nanoparticles. The higher stability may be attributed to the higher surface/volume ratio and also to the increase in the trap-depth with decreasing particle size. When a ZnS:Mn nanocrystal is deformed the peak intensity I_m increases linearly with the increasing height of the load. After I_m, initially the ML intensity decreases at a fast rate, and later on it decreases at a slow rate. The ML in ZnS:Mn nanocrystals can be understood on the basis of the piezoelectrically induced electron detrapping model.