【作者】 张文进；

【导师】 钟新华；

【作者基本信息】 华东理工大学 ， 无机化学， 2014， 博士

【摘要】 在过去20年里,量子点由于具有窄且对称的发射峰、高的光稳定性和高发光效率等优势,已经作为有机染料的替代物应用于很多领域,如显示或发光器件、太阳能电池和生物标记等等。传统上量子点主要依靠“尺寸依赖”来调控光、电性质,这种方法具有一定局限性。为克服这一弊端,在本论文中,我们建立了“结构依赖”、“组分依赖”等方法来代替“尺寸依赖”方法,取得了一定成果。另一方面,随着人们对量子点在健康和能源等领域应用日益推广,开发大批量生产高质量纳米材料的方法已经迫在眉睫,目前大多数性能优异的纳米材料都是通过热注入法得到,这种方法不适于可放大量,高重复性工业化生产要求,此外,高成本和苛刻的实验条件也是不能进行实际应用的原因。我们开发的单锅无注入合成方法,成功实现了克量级高质量纳米晶合成。本学位论文主要包含以下内容：(1)CdTe/CdSe/ZnS核/壳/壳结构量子点我们通过三步法得到此种量子点。首先将CdO,十四烷基磷酸和十八烯在室温下加入到三口烧瓶中,在氮气保护和磁力搅拌下加热到290℃,注入Te前驱体溶液(将Te粉在210℃下溶解在三辛基磷和十八烯的溶液中)并生长3mmin后得到CdTe量子点核。然后将纯化后的CdTe量子点核、十四烷基磷酸、三辛基磷和十八烯在室温下一起加入到三口烧瓶中,升温到150℃,每隔30min分别加入Cd前驱体溶液(将Cd(OAc)2在80℃下溶解在三辛基磷和十八烯的溶液中)和Se前驱体溶液(将Se粉在超声下溶解在三辛基磷和十八烯的溶液中),得到CdTe/CdSe核/壳结构量子点。最后将反应温度降低至135℃,加入一定量二乙基二硫代氨基甲酸锌溶液(将二乙基二硫代氨基甲酸锌在超声下溶解在三辛基磷和十八烯(v/v,1：1)的溶液中),反应30min,再升温至200℃反应30min,最终得到CdTe/CdSe/ZnS核/壳/壳结构量子点。这种量子点的荧光效率高达94%,发光范围为540到825nm。在实验条件选择中,我们采用了具有强配位能力的十四烷基磷酸,这是成功要素之一,另外,采用低温生长壳层技术也是关键一点。通过这种新型“结构依赖”能带隙调控方法得到的高质量荧光在转入水相后仍然能够保持,高的光稳定性是由于宽能带ZnS壳层的包覆可以让电子与空穴限定在CdTe/CdSe内部,从而与外部环境隔离开来。(2)Zn-Cu-In-S/ZnS (ZCIS/ZnS)合金量子点我们通过“组分依赖”能带隙调控方法合成出这种高质量荧光量子点。具体的合成方法是在室温下将金属离子醋酸盐、硬脂酸、十二硫醇和十八烯放入到反应烧瓶中,在氮气保护和磁力搅拌下加热到230℃,注入一定量的S源溶液反应30min得到ZCIS合金量子点核,然后升高温度至240℃,每隔15min注入一定量的Zn前驱体溶液(将Zn(OAc)2在160℃下溶解在油胺和十八烯的溶液中)到反应溶液中,反复5次,最终得至IJZCIS/ZnS合金量子点。最初ZCIS核荧光量子产率小于3%,在包覆ZnS后,可以显著提高到56%,发光范围从518nm到810nm,涵盖了大部分可见光光谱和一部分近红外光谱。实验结果显示Zn/Culn比例、硫源、十二硫醇的量和反应温度都会显著影响合金量子点能带。此外,我们使用巯基十一酸进行配体交换可以将油溶性量子点转入水相中,并保持高荧光量子产率。基于这个优势,在可见光照射下我们将水溶性ZCIS/ZnS量子点进行了降解罗丹明B实验,在2h内就可以将其完全降解,显示出优异光催化性能。(3)Mn:ZnS量子点我们利用成核掺杂技术,具体方法是在室温下将硬脂酸锰、十二硫醇和十八烯加入到反应烧瓶中,在氮气保护和磁力搅拌下将温度升高到250℃,注入一定量的S前驱体溶液,生长1min得到稳定且小尺寸MnS核(2.0nm),然后通过注入一定量的Zn前驱体溶液(将Zn(OAc)2在160℃下溶解在油胺和十八烯的溶液中),生长20min,再降低温度至230℃注入同等量的Zn前驱体溶液,生长20min,实现在核的外面径向生长ZnS壳层,最终得到Mn:ZnS量子点。我们通过紫外吸收光谱、荧光发射光谱、透射电子显微镜和X射线衍射仪表征了Mn：ZnS量子点的光学性质和结构性质。考察了不同实验条件(包括MnS核和ZnS壳层的反应温度、S前驱体溶液的量、十二硫醇的量和Zn/Mn比例)的影响。使用十二硫醇作为配体可以增强形成小尺寸稳定的MnS核的重复性,从而得到高质量掺杂结构荧光量子点。设计ZnS壳层生长温度实现了Mn离子在掺杂结构量子点中的扩散平衡。(4)Cu:ZnxCd1-xS、Cu:Zn-In-S和Cu,Mn:Zn-In-S量子点我们利用单锅无注入法,具体是在室温下将金属醋酸盐、S粉、十二硫醇、油胺和十八烯加入到反应烧瓶中,然后在氮气保护和磁力搅拌下升高温度到220℃并反应30min就可以方便得至Cu:ZnxCd1-xS、Cu:Zn-In-S和Cu,Mn:Zn-In-S掺杂量子点。三种掺杂量子点的发光范围可以覆盖整个可见光光谱和部分近红外光谱(从450到810nm),荧光量子产率平均在50%-80%。此外掺杂发光可以通过改变主体材料元素比例、Mn或Cu离子浓度和反应温度等条件方便调控。通过配体交换后,所得水溶性量子点荧光量子效率能够保持最初油溶性量子点的75%以上,并且具有高的热稳定性(高达250℃),长的荧光寿命(亚微秒)。更重要的是我们将不含重金属Cd的低毒性Cu:Zn-In-S/ZnS量子点材料作为发光活性层,组装出量子点发光二极管(QD-LEDs)器件,它的启动电压为3.6V,可以比拟一般QD-LEDs水准,最大荧光强度可以达到220cd m-2(在8.5eV),在0.41mAcm-2注入电流密度下,发光效率(LE)和功率效率(PE)分别为2.45cdA-1和2.14lm W-1,对应亮度为10cdm-2。我们还将Cu, Mn:Zn-In-S/ZnS量子点作为光转换层装配成白光发光二极管(WLED)器件,显示出CRI高达91、发光效率为51lm/W的标准白光。总之,我们证实这些量子点有潜力作为低毒材料用于LEDs和生物标记中。(5)克量级合成核壳结构量子点、CdSe多脚棒纳米晶及不同形貌CdS纳米晶我们利用单锅无注入法分别制备出了三种半导体纳米晶。第一种是核壳结构量子点(CdS/ZnxCdi1-xS, CdSe/ZnxCdi1-xS和CdTe/ZnxCd1-xS),其壳层为组成梯度变化的合金材料。具体方法是在室温下将CdO、Zn(NO3)2、硫族元素、三辛基磷、硬脂酸和十八烯加入到反应烧瓶中,在氮气保护和磁力搅拌下加热到250℃反应60min,最终得到核壳结构量子点(CdS/ZnxCd1-xS, CdSe/ZnxCd1-xS和CdTe/ZnxCd1-xS)。通过简单地改变反应物种类和配体量,它的发光范围可以从紫光一直调控到近红外区域(400-820nm),发光效率可以高达80%,并且通过配体交换转入水相后仍然可以保持油溶性量子点的量子产率。通过该反应我们很方便地制备出克量级各种颜色(绿色、黄色和红色)高质量荧光量子点,体现出该合成方法大批量生产高质量荧光纳米晶的潜力。第二种是CdSe多脚棒半导体纳米晶。具体的合成方法是在室温下将CdO和Se粉作为反应原料加入到含有三辛基磷、油酸和石蜡反应溶剂的反应烧瓶中,升高温度到210℃生长10min,得到克量级CdSe多脚棒纳米晶。我们考察了不同反应条件(包括反应温度、配体性质和种类、Cd/Se匕例和反应物性质)对CdSe多脚棒纳米晶性质的影响。在包覆ZnS壳层之后,荧光量子产率可以显著提高到85%。第三种是各种各样形状(球形,四面体,枝杈状和花状结构)的CdS纳米晶。具体方法是在室温下将CdO和S粉作为直接反应原料加入到含有三辛基磷、油酸和石蜡反应溶剂的反应烧瓶中,升高温度到230℃生长10min,得到克量级形貌可控的CdS纳米晶。其形貌变化机理与核的结构及单体浓度有关。此外,所得各种形貌(球形,四面体,枝杈状和花状结构)的CdS产品对于降解有机染料显示出优异光催化性能,其中球形CdS纳米晶相对于其他形貌CdS纳米晶比较低的光催化性能可以归因于低的电子-空穴分离效率。综上所述,我们发明的单锅无注入法能够满足工业化生产所需的可升级、低成本及可重复性。更多还原

【Abstract】 In the past two decades, quantum dots (QDs) have been widely studied and applied in many fields such as light-emitting diodes (LEDs), solar cells and bio-sensor, asanalternativetoorganic dyes, because of their outstanding properties of narrow and symmetric emission peak, high stability, high photoluminescence quantum yield, and so on. Traditionally, the photoelectronic properties of QDs is tuned via the variation of the particle size, while the size-tuning route is limited in many fields. To solve this problem, we established the "structure-tuning" and "composition-tuning" method to tune the bandgap of QDs. On the other hand, with more wide application of quantum dots in health and energy field, to develop massive synthesis of high quality nano-materials isa hot issue. So far hot-injection synthetic method is commonlyused in synthesizingmostnano-materials, which cannot satisfy the requirement of scalable and reproducible production in industrial application. Moreover, high cost and strict experiment conditions also impede the industrial application of QDs. However, the one-pot non-injection synthesis, as we described, has achieved the goal of industrial application. This dissertation contains the following content:(1) CdTe/CdSe/ZnS core/shell/shell nanostructureTypically, CdO,1-tetradecylphosphonic acid, and1-octadecene were loaded in a three-neck flask clamped in a heating mantle, which was raised to290℃under an argon. At this temperature, Te precursor solution was quickly injected into the reaction flask and kept at this temperature for30min to the grow the CdTe core. Then purified CdTe core,1-tetradecylphosphonic acid, trioctylphosphine and1-octadecene were loaded in a three-neck flask clamped in a heating mantle, which was raised to150℃under an argon, an equimolar amount of the Cd precursor stock solutions, obtained by dissolving Cd(OAc)2in trioctylphosphine and1-octadecene at80℃, and Se precursor stock solutions, obtained by dissolving Se powder in trioctylphosphine and1-octadecene using sonication, was added alternately via a syringe at a30min interval for the growth of CdTe/CdSe core/shell nanocrystals (NCs). the addition of the Cd/Se precursors was stopped and the reaction temperature was lowered down to135℃for the following overgrowth of the ZnS shell. When the temperature of the reaction system stabilized at135℃, a certain amount of zinc diethyldithiocarbamate stock solution, obtained by dissolving zinc diethyldithiocarbamate in trioctylphosphine and1-octadecene (v/v,1:1) at room temperature by sonication, was added and kept at this temperature for30min, and then the temperature was raised to200℃and maintained for another30min to get CdTe/CdSe/ZnS Core/Shell/Shell QDs. The CdTe/CdSe/ZnS QDs possess photoluminescence quantum yields (PL QY) as high as94%and the emission wavelength of the obtained nanostructure can span from540to825nm. In the experiment, an effective shell-coating route was developed for the preparation of CdTe/CdSe core/shell nanostructures by selecting capping reagents with a strong coordinating capacity which is one of the factors of success. In addition, adopting a low temperature for shell deposition is also the key point. The obtained high quality of fluorescence through the kind of new structure depending on the band gap adjustment methods can still be kept when transferred into water phase. The high PL stability of the obtained CdTe/CdSe/ZnS QDs is mainly derived from the passivation effect of the outer ZnS layer with a substantially high bandgap, which effectively confines the excitons within the CdTe/CdSe interface and isolates them from the solution environment.(2) ZnCuInS/ZnS (ZCIS/ZnS) alloyed nanocrystalsThe high quality fluorescence QDs have been obtained through the "structure-tuning" method to tune the bandgap of QDs. In a typical procedure, the acetate salts of the corresponding metals, stearic acid, dodecanethiol, and octadecene were loaded in a50-mL three-neck flask clamped in a heating mantle. The mixture was heated to230℃under argon flow. Then S precursor solution, obtained by dissolving sulfur in octadecene at120℃, was injected into the reaction system and kept at this temperature for30min to allow growth of ZCIS NCs. The reaction temperature was raised to240℃for the following overgrowth of the ZnS shell. Zn stock solution (zinc acetate dissolved in oleylamine and1-octadecene at160℃) was injected into the reaction mixture in5batches with a time interval of15min to obtained ZCIS/ZnS NCs. The plain ZCIS NCs did show PL emission but with quite low PL QY (typically below3%). With the deposition of ZnS shell around the ZCIS core NCs, the PL QY increased substantially with a maximum value of56%and emission wavelength tunable from518to810nm covering most part of the visible light spectrum and near infrared spectrum. The various experimental variables, including the Zn/CuIn ratio, amount of sulfur and dodecanethiol, and reaction temperature, have a significant effect on the bandgap of the obtained alloyed NCs. The high PL emission efficiency of the ZCIS/ZnS NCs can also be preserved after phase transfer via ligand replacement. Besides the excellent optical properties, the obtained ZCIS/ZnS NCs also exhibit promising photocatalytical activity in the degradation of rhodamine B. (3) Mn:ZnS QDsOur synthetic method based on "nucleation-doping" strategy. Typically, manganese stearate, dodecanethiol, and octadecene were loaded into a three-neck flask. Then the reaction system was filled with N2, and the temperature was further raised to250℃. At this temperature, S precursor solution, obtained by dissolving sulfur powder in octadecene at120℃, was injected into the reaction system and kept at this temperature for1min to allow growth of stable and small size of MnS nanoclusters (2nm). One half Zn stock solution (zinc acetate dissolved in oleylamine and1-octadecene at160℃) was injected to the solution and kept at250℃for20min, then the temperature was set to230℃, the other half Zn stock solution was injected to the solution and kept at230℃for20min to obtained Mn:ZnS QDs. The optical properties and structure of the obtained Mn:ZnS QDs have been characterized by UV-vis, PL spectroscopy, transmission electron microscopy, and X-ray diffraction. The resulting nearly monodisperse d-dots were found to be of spherical shape with a zinc-blende crystal structure. The influences of various experimental variables, including the reaction temperature for the MnS core nanocluster and ZnS host material, the amount of S precursor solution, dodecanethiol, as well as Zn/Mn ratio have been systematically investigated. The use of dodecanethiol as capping ligand ensured the reproducible access to a stable small-sized MnS core. This paves the way for reproducibly obtaining highly luminescent doped QDs. Programmed overcoating temperature for growth of ZnS shell was employed to realize balanced diffusion of the Mn ions in the Mn:ZnS QDs.(4) Cu:ZnxCd1-xS、 Cu:Zn-In-S and Cu, Mn:Zn-In-S QDsOur synthetic method based on "single-step noninjection" synthetic approach. In a typical procedure, the acetate salts of the acetate salts of the corresponding metals, S powder, dodecanethiol, oleylamine and octadecene were loaded in a three-neck flask clamped in a heating mantle. Then the reaction system was filled with N2, and the temperature was further raised to250℃, and kept at this temperature for30min to obtained Cu:ZnxCd1-xS, Cu:Zn-In-S and Cu, Mn:Zn-In-S QDs respectively, the resulting doped QDs show composition-tunable PL emission over the entire visible spectral window and extending to the near-infrared spectral window (from450to810nm), the average dopant emission show50-80%PL QY. In addition, the doped emission can be convenient tuned by changing the ratios of host material elements, Mn or Cu ion concentration and reaction temperature. Importantly, the initial high PL QY of the obtained doped QDs in organic media can be preserved when transferred into aqueous media via ligand exchange. Furthermore, electroluminescent devices with good performance (with a maximum luminance of220cd m-, low turn-on voltages of3.6V) have been fabricated with the use of these Cd-free low toxicity Cu:Zn-In-S/ZnS QDs as an active layer in these QD-based LEDs. we explored the possibility of using Cu, Mn:Zn-In-S/ZnS QDs as colour converting materials for white light-emitting applications. The devices exhibit high colour rendering index of91, luminous efficiency of51lm/W. Overall, these materials have promising potential as less toxic NCs for applications in LEDs and biolabeling.(5) Gram-scaled synthesis of core-shell structure of QDs, CdSe multipod NCs and shape-tunable CdS NCsThe three kinds of semiconductor NCs have been obtained respectively through the "single-step noninjection" synthetic approach. The first is high quality core/shell QDs (CdS/ZnxCd1-xS, CdSe/ZnxCd1-xS, and CdTe/ZnxCd1-xS) with shell material composed of gradient alloy structure. In a typical procedure, CdO, Zn(NO3)2, chalcogenide elements, trioctylphosphine, stearic acid and octadecene were loaded in a three-neck flask clamped in a heating mantle at air. the temperature was further raised to250℃, and kept at this temperature for30min to obtained core/shell QDs (CdS/ZnxCd1-xS, CdSe/ZnxCd1-xS, and CdTe/ZnxCd1-xS). With simple variation of reaction recipe (reactants and feeding ratio), luminescence color of the resulting QDs can be conveniently tuned from violet to near-infrared (400-820nm). The emission efficiency of the as-prepared QDs can be up to80%. Moreover, the high emission efficiency can be preserved after QDs transferred into aqueous media via ligand exchange. Gram-scaled green, yellow, and red emissive core/shell QDs can be obtained in one bath reaction. And second is the CdSe multipod NCs. In a typical procedure, CdO, Se powder, trioctylphosphine, oleic acid and paraffin were loaded in a three-neck flask clamped in a heating mantle. Then the reaction system was filled with N2, the temperature was further raised to250℃, and kept at this temperature for10min to obtained CdSe multipod NCs. The influence of various experimental variables, including reaction temperature, nature and amount of surfactants, Cd-to-Se ratio, and the nature of reactants, on the morphology of the obtained CdSe NCs have been systematically investigated. After deposition of ZnS shell around the CdSe multipod NCs, the PL QY of the obtained CdSe/ZnS can be up to85%. The third is the CdS NCs with a wide variety of shapes including spheres, tetrahedrons, and branched and flower-like structures. In a typical procedure, CdO, S powder, trioctylphosphine, oleic acid and paraffin were loaded in a three-neck flask clamped in a heating mantle. Then the reaction system was filled with N2, the temperature was further raised to230℃, and kept at this temperature for30min to obtained the shape-controlled CdS NCs. The shape-controlled growth mechanism could be explained by the nuclei structure and monomer concentration. All the CdS nanocrystal samples with different morphologies exhibit good photocatalytic activity for degradation of dyes. The observed lower photocatalytic activity of the sphere-shaped CdS NCs could be ascribed to the higher PL QY relative to those with other morphologies, which results in low electron-hole separation efficiency. Overall, our reported preparation approach can satisfy the requirements of industrial production bearing the advantage of low-cost, reproducibility and scalability.更多还原