【作者】 王超；

【导师】 冯守华；

【作者基本信息】 吉林大学 ， 无机化学， 2019， 博士

【摘要】 荧光量子点（QDs）由于具有带隙可调、光电转换效率优异、发光效率高和可溶液制备等优点,在太阳能电池、发光二极管、生物荧光标记、生物传感等方面具有广阔的应用前景。早期合成的量子点以二元体系为主,主要包括II-VI族、III-V族、IV-VI族QDs,自20世纪80年代以来,关于其合成和性质研究都取得了巨大的进展,尤其以CdSe等为代表的二元量子点显示出了优异的光学性质,目前该材料在显示领域已进入商业化应用阶段,这些二元半导体量子点的带隙与光学/光电性质主要依赖于尺寸和材料的种类。随着量子点科学的发展,研究进一步拓展到了I-III-VI族等三元或四元量子点,多元量子点的特点是其带隙与光学性质不仅可以通过量子点的尺寸和材料的种类来调控,也可通过其组成进行调控,因而,对于多元量子点来说,具有更多方式调控光学/光电性质,进一步拓宽了量子点在光电、生物领域中的研究与应用。在三元半导体纳米材料中,I-III-VI族半导体材纳米材料（如Cu-In-S、Ag-In-S、Ag-Ga-S）是研究最成熟的体系,其合成、性质研究及应用受到研究者的广泛关注。例如三元Cu-In-S/Se量子点由于其优异的光学/光电性质广泛应用于太阳能电池、生物成像等研究领域。一个显著的问题是这类材料大都包括III族的铟元素,由于地球储量的限制,该材料较为稀少,寻找III族铟材料的替代物引起了研究者的兴趣。Cu-Fe-S基材料中含有Fe元素,地球储量丰富,价格低廉,具有较低且可调带隙,最近受到了越来越多的关注。早年关于Cu-Fe-S纳米材料的合成工作很少,主要集中在Cu-Fe-S纳米线、纳米棒的合成方面。2010年以后,Cu-Fe-S纳米材料的研究逐年上升,但合成的纳米晶通常尺寸较大（几十纳米以上,甚至微米级别）,因此小尺寸Cu-Fe-S多元纳米晶的可控合成与组分控制具有十分重要的研究价值。与二元量子点相比,Cu-Fe-S多元纳米晶不仅仅可以通过控制纳米晶的尺寸调控量子点的带隙结构,更能通过化学组分实现量子点吸收带边的调控,使吸收带边可从紫外光区扩展到近红外光区,更有利于其在生物检测领域中的应用。截止到目前,关于Cu-Fe-S纳米材料荧光性质的报道几乎没有,利用无机壳层钝化量子点或者引入第四种合金元素,使其缺陷态非辐射复合中心减少,提高量子点荧光量子产率和延长荧光寿命,同时控制量子点的尺寸和组分,实现Cu-Fe-S基量子点荧光光谱可调,是一项非常有研究意义的工作。基于此,本文在Cu-Fe-S基量子点材料的可控合成及其光学/光电性质调控方面开展了一系列研究工作,主要研究内容如下:1.发展了一种合成小尺寸Cu-Fe-S量子点的热注入合成路线,通过加入不同化学计量比的原料,调控不同反应温度,成功地合成了CuFeS₂和Cu₅FeS₄两种三元Cu-Fe-S不同晶型结构的量子点,通过控制反应温度,实现了量子点尺寸可调;系统研究了Cu-Fe-S量子点的光学性质,揭示了Cu-Fe-S量子点尺寸与光学性质之间的变化规律,结果表明,Cu-Fe-S量子点的吸收光谱根据不同组成展现出两种类型吸收峰,随粒子尺寸增加,两种吸收峰均显示了符合量子尺寸效应的红移;通过制备光电器件,探索研究了Cu-Fe-S量子点的光电性质,实验结果表明,CuFeS₂量子点表现出了更好的光电响应,其光电流相比暗态时可提高约10倍。2.以制备的三元Cu-Fe-S量子点为核,通过高温热注入方式,采用离子层吸附反应法,利用Cd（OA）₂和硫为反应前体,以十八烯为稳定剂,通过调控核的尺寸和壳层厚度两种方式成功实现了CuFeS₂@CdS核壳结构量子点的可控制备,并系统研究了CuFeS₂@CdS核壳量子点的光学性质。选择不同尺寸的Cu-Fe-S量子点为核,合成了CuFeS₂@CdS核壳量子点,实现了尺寸及荧光性质的调控,荧光发射峰位从780 nm至820 nm范围内可调,核壳量子点荧光效率可达15%;固定核的尺寸,通过改变Cd前体的投入量调控CdS壳层厚度,进而调控了CuFeS₂@CdS核壳量子点的光谱,随壳层厚度增加,荧光发射峰可从780 nm调至822 nm;稳定性研究实验表明,在光照下和室温放置一段时间后,CuFeS₂@CdS核壳量子点表现出了良好的化学稳定性和光化学稳定性。3.在制备CuFeS₂@CdS核壳量子点基础上,采用一步法,将铜、铁和镉的前体、硫粉、配体和溶剂十八烯混合,通过高温热注入方式首次实现了四元Cd-Cu-Fe-S量子点的可控制备。系统的研究了前体投入量、反应时间和反应温度的影响,通过改变反应温度,制备了尺寸可调（3.0 nm⁸.0 nm）的四元Cd-Cu-Fe-S量子点。结构研究表明:制备的四元纳米晶是立方结构,发射波长从630 nm到950 nm范围内可调;通过固定反应温度,改变前体投入量,制备了不同组成的Cd-Cu-Fe-S四元量子点,研究表明,其光学性质不仅依赖于尺寸,而且受组成调控。获得的四元量子点具有高达57%的荧光量子效率;稳定性和光电研究实验结果表明:Cd-Cu-Fe-S量子点不仅具有良好的化学稳定性,而且表现出优异的光电流响应,其光电流相比暗态时可提高约20倍。综上,本论文对Cu-Fe-S基量子点的合成与光学/光电性质研究进行了系统研究。实现了不同组分、不同尺寸的三元Cu-Fe-S量子点、CuFeS₂@CdS核壳量子点的可控制备,进而发展一步法获得了Cd-Cu-Fe-S四元量子点,并通过控制量子点的尺寸实现了荧光光谱的调控,最终获得了稳定的、发光范围可调和量子效率高的荧光量子点。光电性质研究表明,该类型纳米材料具有良好的光电响应,是一类新型的光电纳米材料,具有潜在的应用前景。更多还原

【Abstract】 In past decades,fluorescent quantum dots（QDs）have been widely studied due to their unique properties such as tunable bandgap,excellent photoelectric conversion efficiency,high luminescence efficiency and soluble preparation.Luminescent colloidal semiconductor nanocrystals are of significant technology interest as they impact many applications including light emitting diodes（LEDs）,solar cells,biomedical labeling and biosensors.While existing examples of light emitting semiconductor nanocrystals such as II-VI,II-V,III-V,IV-IV have size tunable band gap,which show various emission spectra depending on the sizes.At an extend work,I-III-VI semiconductor nanocrystals such as CuInS₂ have been successfully prepared recently due to not only their size tunable bands but composition dependent optical properties.Recently,Cu-Fe-S QDs with bandgap from 0.5 eV to 2.1 eV,a member of I-III-VI family QDs,has been identified as a candidate in the optoelectronic applications due to their unique properties.However,no photoluminescence is observable from existed Cu-Fe-S QDs,although their colloidal nanoparticles have been reported in literature.To further insight into the optical properties,the synthesis and characterization of Cu-Fe-S QDs were systematically investigated in current thesis.The main content of the thesis are as follows:1.Both CuFeS₂ and Cu₅FeS₄ QDs were synthesized by hot injection method.The size of as prepared samples was controllable by changing the reaction temperature.As a result,the CuFeS₂ QDs was obtainable in a size range of 3-6 nm.Accordingly,their absorption peak can be tuned from 475 to 493 nm.In contrast,the Cu₅FeS₄ QDs with a size range of 4-7 nm were obtained,showing tunable absorption peak from 535-610nm.Importantly,these particles showed high monodispersity and good size distribution.To study the optoelectronic properties of these QDs,thin-film optoelectronic devices were fabricated with the two kinds of samples separately including CuFeS₂ QDs and Cu₅FeS₄ QDs.Experimental result indicated that the device based on CuFeS₂ QDs show a significant increase in current by ca.10 times under illumination relative to the dark state,indicating its potential application in the field of photovoltaic.2.Improvement of the optoelectronic properties of semiconductor nanocrystals is still a prominent research topic.One of the most important approaches is fabricating composite type-I core-shell structures which exhibit improved properties.In this chapter,CdS shell was used to passivate the CuFeS₂ QDs by preparation of CuFeS₂@CdS core-shell structure.The as-synthesized sample showed photoluminescence emission,which could be tunable by changing the core size and shell thickness.As a result,the as-prepared sample showed tunable emission from 780to 822 nm.Furthermore,the core-shell samples showed high quantum efficiency（reach up to 15%）,and good chemical and photochemical stability.3.A simple synthetic route for preparation of colloidal Cd-Cu-Fe-S QDs for the first time was developed by hot-injection method.The effects of different reaction conditions including reaction time,additional amount of precursors and reaction temperature were detailed investigated.As a result,quaternary Cd-Cu-Fe-S QDs exhibiting a strong size tunable photoluminescence were synthesized for the first time by tuning the reaction temperature from 120°C to 210°C.The preparation procedure involved cadmium acetate,copper acetate,iron chloride,and sulfur powder dissolved in oleylamine as precursors.The wavelength of the emission could be tuned from 630nm to nearly 1000 nm by only changing the size of the Cd-Cu-Fe-S QDs from 3.0 nm to 8.0 nm.Interestingly,these QDs possess a relatively high quantum yield of over 57%and excellent chemical stability without coating any wide-band-gap shell materials.The study on the optoelectronic properties of Cd-Cu-Fe-S QDs,where an order of photocurrent was enhanced under AM1.5 illumination,demonstrated their suitability as optically active components to fabricate optoelectronic devices.In conclusion,the work in this dissertation serves to explore the synthesis and optical/optoelectronic properties of Cu-Fe-S quantum dots.Controllable fabrication of Cu-Fe-S QDs and CuFeS₂@CdS core-shell QDs has been realized.And a one-step method has been developed to obtain Cd-Cu-Fe-S quaternary quantum dots.By controlling the size of the quantum dots,the fluorescence spectrum can be tuned to near infrared region.Through the study of the stability,we finally obtain stable fluorescent quantum dots with a strong tunable photoluminescence and a relative high quantum yield,demonstrating their suitability and potential in practical applications.更多还原