ZnO@GQDs核壳结构量子点的制备及性能研究

采用原位聚合法制备了以ZnO量子点为核、石墨烯量子点(GQDs)为壳的ZnO@GQDs核壳结构量子点。通过TEM和HR-TEM对量子点进行形貌和结构的分析表征。结果表明,合成的ZnO@GQDs核壳结构量子点为球形,粒径为~7 nm,且尺寸均匀。PL光谱研究表明,新型量子点的发射峰位于369 nm,发光峰窄、强度高;相对于ZnO的本征发射峰,GQDs的引入使得ZnO@GQDs核壳量子点的荧光发射峰出现蓝移、强度变高,从而使复合量子点的荧光具有较纯的色度和较高的强度,说明GQDs的引入具有协同优化效应。该量子点有望应用于LED显示器件。     

低强度飞秒激光激发下CdTe和CdTe/CdS核壳量子点的荧光上转换研究

利用400 nm和800 nm不同波长的低强度飞秒激光,对CdTe和CdTe/CdS核壳量子点溶胶进行激发,研究其稳态和时间分辨荧光性质.800 nm飞秒激光激发下,CdTe和CdTe/CdS核壳量子点产生上转换发光现象,上转换荧光峰与400 nm激发下的荧光峰相比蓝移最多达15 nm,而且蓝移值与荧光量子产率有关.变功率激发确认激发光功率与上转换荧光强度间满足二次方关系,时间分辨荧光的研究表明荧光动力学曲线服从双e指数衰减.提出表面态辅助的双光子吸收模型是低激发强度上转换发光的主要机理.CdTe和CdT 关键词： CdTe量子点 CdTe/CdS核壳量子点 时间分辨荧光 上转换荧光     

溶剂对石墨烯量子点荧光性质的影响

采用柠檬酸热解法制备了石墨烯量子点(GQDs),研究了非极性溶剂戊烷,极性溶剂乙醇、丙酮、乙二醇对GQDs荧光性质的影响。透射电子显微镜(TEM)和原子力显微镜(AFM)图像表明,制备的GQDs尺寸分布在2~12 nm(平均尺寸为4.9 nm),分散均匀,高度分布在0.5~2 nm。吸收光谱表明,GQDs具有明显的紫外吸收特性,吸收峰位于259 nm和274 nm。光致发光谱表明,GQDs的发光具有明显的溶剂依赖性。GQDs在极性溶剂乙醇、丙酮、乙二醇中,发光峰的位置依赖于激发波长,发射波长在可见光区。而在非极性溶剂戊烷中,GQDs表现出对激发波长不依赖的荧光性能,且发射波长在近紫外。     

聚丙烯酸修饰核壳结构水溶性量子点的制备及表征

先用硫脲修饰的量子点为核,再用聚丙烯酸包覆,并用聚乙烯吡咯烷酮K-30为稳定剂,合成粒径分布均匀、性能稳定的核壳结构水溶性量子点荧光体。采用荧光发射光谱、红外光谱和透射电镜对样品进行表征并探索核量子点在聚丙烯酸聚合物溶液中含量对量子点荧光体的影响。结果表明:聚丙烯酸修饰后量子点粒径分布更均匀;荧光发射主峰由548nm蓝移到448nm。红外光谱图中2 092.8和1 384.3cm-1分别归属于羧基的CO和C—O伸缩振动,1 644.5cm-1归属为酰胺键的CO伸缩振动,核量子点在聚丙烯酸聚合物溶液中最佳含量为2.67mg.mL-1。该量子点制备方法简单易行,具有较好的稳定性及高荧光量子效率,为进一步应用于生物标记奠定基础。     

核壳型ZnS∶Cu/ZnS量子点的制备及发光性质

本文采用水相合成方法制备了ZnS∶Cu量子点并进行了ZnS壳层修饰,研究了壳层厚度对ZnS∶Cu量子点光学性质的影响,采用TEM、XRD、PL、PLE和UV-Vis等测试方法对其进行了表征。实验结果表明,合成的ZnS∶Cu/ZnS量子点为立方闪锌矿,尺寸分布均匀呈球形,分散性良好,经过壳层修饰平均粒径由2 nm增加到3.2 nm。随着ZnS壳与ZnS核量的比的增加,量子点的PLE激发峰位置和UV-Vis吸收谱线出现红移,也说明了量子点的尺寸增大,证明ZnS在ZnS∶Cu量子点的表面生长,形成了核壳结构的ZnS∶Cu/ZnS量子点。随着壳层增厚,量子点与铜离子发光中心相关的发射峰强度先增大后减小,当壳核比n_s/n_c=2.5时,发光强度达到最大。     

ZnO对硫硒化镉量子点玻璃发光性能的影响

以CdS、Se、Zn粉和玻璃基质为原料,采用高温熔融法制备了CdS_xSe_(1-x)量子点硅酸盐玻璃,研究了ZnO含量对CdS_xSe_(1-x)量子点发光玻璃微观结构及发光性能的影响。结果表明:ZnO对CdS_xSe_(1-x)量子点玻璃的发光性能有显著的影响,紫外-可见吸收光谱和荧光光谱分析结果说明在470 nm蓝光激发下,掺Zn O的CdS_xSe_(1-x)量子点玻璃中CdS_xSe_(1-x)量子点处于强限域区,出现了强烈的带边激子发射现象,证明量子点具有明显的量子尺寸效应。当样品中ZnO的质量分数为13%时,荧光光谱峰强最大,半峰宽最窄。     

脂溶性CdSe/ZnS量子点脂质体复合物的制备及表征

在油相中成功合成了脂溶性CdSe/ZnS核壳量子点纳米粒,粒径平均为4.5 nm,量子产率达29%,发射波长为540 nm。通过薄膜分散法,以蛋黄卵磷脂、胆固醇为膜材,将脂溶性的CdSe/ZnS核壳量子点包覆于脂质体磷脂双分子层中,由于磷脂分子的两亲性,使得脂溶性的CdSe/ZnS核壳量子点同时又具有亲水性。通过透射电镜对脂质体形态进行了表征,倒置荧光显微镜证实了发光CdSe/ZnS核壳量子点成功包埋于脂质体双分子层中,包裹的发光CdSe/ZnS核壳量子点具有更稳定的发光及抗光漂白性质。     

ZnO/ZnS核-壳量子点的双光子吸收效应

利用飞秒激光Z-扫描与泵浦-探测技术,研究了室温下ZnO/ZnS与ZnO/ZnS/Ag核-壳胶体量子点的双光子吸收效应.研究发现:ZnO基核-壳量子点的本征双光子吸收系数比ZnO体材料增大了3个数量级;测量得到的660 nm处的ZnO/ZnS核-壳量子点双光子吸收截面约为4.3×10^-44 cm⁴·s·photon^-1,比相应的ZnS、ZnSe及 CdS量子点大2个数量级;当ZnO/ZnS核-壳量子点镶嵌了银纳米点时,非线性吸收有所增强.ZnO基复合纳米结构的双光子吸收增强可归因于量子限域与局域场效应.     

CdS_xSe_(1-x)/ZnS(核/壳)量子点的光谱截面及其掺杂光纤的传光特性

测量了不同组份比例x的CdS_xSe_(1-x)/ZnS(核/壳)量子点的吸收谱和发射谱,确定了量子点的吸收系数、吸收截面和发射截面.量子点吸收截面随粒径的增大而增大、随x的增大而减小.采用紫外固化胶,制备了掺杂浓度为0.1~5mg/mL的CdS_(0.4)Se_(0.6)/ZnS量子点光纤,测量了不同掺杂浓度量子点光纤中473nm泵浦功率的吸收衰减速率.吸收衰减速率和吸收截面弱关联于掺杂浓度.测量了光致荧光光谱强度随光纤长度和量子点浓度的变化.量子点光纤的光致荧光峰值强度随掺杂浓度和光纤长度变化而变化,且存在一个与最大峰值强度对应的饱和掺杂浓度和光纤长度.本文的实验结果有助于进一步构建新型的CdS_xSe_(1-x)/ZnS量子点增益型光电子器件.     

水溶性CdTe量子点的稳态和纳秒时间分辨光致发光光谱

报道了以飞秒脉冲激光为激发光源的水溶性CdTe量子点(QDs)的稳态荧光光谱和纳秒时间分辨荧光光谱.实验发现CdTe量子点的荧光光谱峰值位置随激发波长变化发生明显移动，激发脉冲波长越长，荧光峰位红移越大.荧光动力学实验数据显示，在400nm和800nm脉冲激光激发下，水溶性CdTe量子点的荧光光谱中均含有激子态和诱捕态两个衰减成分，两者的发射峰相距很近，诱捕态的发射峰波长较长.在800nm脉冲激光激发下的诱捕态成分占总荧光强度的比重比400nm激发下的约高3倍，其相对强度的这种变化导致了稳态荧光发射峰位的红移. 关键词： CdTe 量子点 时间分辨 荧光光谱 上转换荧光     

Photoluminescence quenching of CdTe/CdS core-shell quantum dots in aqueous solution by ZnO nanocrystals

Photoluminescence (PL) properties of 3-mercaptopropionic acid (MPA) coated CdTe/CdS core-shell quantum dots (QDs) in aqueous solution in the presence of ZnO colloidal nanocrystals were studied by steady-state and time-resolved PL spectroscopy. The PL quenching of CdTe/CdS core-shell QDs with addition of purified ZnO nanocrystals resulted in a decrease in PL lifetime and a small red shift of the PL band. It was found that CdTe(1.5 nm)/CdS type II core-shell QDs exhibited higher efficiency of PL quenching than the CdTe(3.0 nm)/CdS type I core-shell QDs, indicating an electron transfer process from CdTe/CdS core-shell QDs to ZnO nanocrystals. The experimental results indicated that the efficient electron transfer process from CdTe/CdS core-shell QDs to ZnO nanocrystals could be controlled by changing the CdTe core size on the basis of the quantum confinement effect.     

Synthesis and characterization of graphene quantum dots and their size reduction using swift heavy ion beam

Graphene quantum dots (GQDs) are nanosized fragments of graphene displaying quantum confinement effect. They have shown to be prepared from various methods which include ion beam etching of graphene. However, recently the modification of the GQDs has garnered tremendous attention owing to its suitability for various applications. Here, we have studied the effect of swift ion beam irradiation on the properties of GQDs. The ion beam treatment on the GQDs exhibited the change in observed photoluminescence of GQDs as they exhibited a blue luminescence on excitation with longwave UV (≈365?nm) due to the reduction in size and removal of the ethoxy (–C–O–C–) groups present on the quantum dots. This was confirmed by transmission electron microscopy, particle size analysis, and Fourier transform infrared spectroscopy.     

Recent Advances in Graphene Quantum Dots for Fluorescence Bioimaging from Cells through Tissues to Animals

Graphene quantum dots (GQDs) have attracted tremendous attention in recent years. In this review, the recent developments are summarized in the synthesis, edge functionalization, and cyctotoxicity of GQDs, followed by presenting a focused overview on their current applications for in vitro fluorescence imaging in cells and tissues as well as in vivo macroscopic and microscopic imaging in animals. Challenges and opportunities in the development of GQDs for bioimaging are also discussed.     

Preparation of water-soluble CdTe/CdS core/shell quantum dots with enhanced photostability

CdTe/CdS core/shell quantum dots (QDs) have been synthesized in an aqueous phase using thioacetamide as a sulfur source. The quantum yield was greatly enhanced by the epitaxial growth of a CdS shell, which was confirmed by X-ray photoelectron spectroscopy (XPS) results. The quantum yield of as-prepared CdTe/CdS core/shell QDs without any post-preparative processing reached 58%. The experimental results illustrate that the QDs with core/shell structure show better photostability than thioglycolic acid (TGA)-capped CdTe QDs. The cyclic voltammograms reveal higher oxidation potentials for CdTe/CdS core/shell QDs than for TGA-capped CdTe QDs, which explains the superior photostability of QDs with a core/shell structure. This enhanced photostability makes these QDs with core/shell structure more suitable for bio-labeling and imaging.     

Physical reasons of emission transformation in infrared CdSeTe/ZnS quantum dots at bioconjugation

The core/shell CdSeTe/ZnS quantum dots (QDs) with emission at 780–800 nm (1.55–1.60 eV) have been studied by means of photoluminescence (PL) and Raman scattering methods in the nonconjugated state and after conjugation to different antibodies (Ab): (i) mouse monoclonal [8C9] human papilloma virus Ab, anti-HPV 16-E7 Ab, (ii) mouse monoclonal [C1P5] human papilloma virus HPV16 E6+HPV18 E6 Ab, and (iii) pseudo rabies virus (PRV) Ab. The transformations of PL and Raman scattering spectra of QDs, stimulated by conjugated antibodies, have been revealed and discussed.The energy band diagram of core/shell CdSeTe/ZnS QDs has been designed that helps to analyze the PL spectra and their transformations at the bioconjugation. It is shown that the core in CdSeTe/ZnS QDs is complex and including the type II quantum well. The last fact permits to explain the nature of infrared (IR) optical transitions (1.55–1.60 eV) and the high energy PL band (1.88–1.94 eV) in the nonconjugated and bioconjugated QDs. A set of physical reasons has been analyzed with the aim to explain the transformation of PL spectra in bioconjugated QDs. Finally it is shown that two factors are responsible for the PL spectrum transformation at bioconjugation to charged antibodies: (i) the change of energy band profile in QDs and (ii) the shift of QD energy levels in the strong quantum confinement case. The effect of PL spectrum transformation is useful for the study of QD bioconjugation to specific antibodies and can be a powerful technique for early medical diagnostics.     

Determination of Thermal History by Photoluminescence of Core‐Shelled Quantum Dots Going Through Heating Events

A kind of novel thermal history nanosensors are theoretically designed and experimentally demonstrated to permanently record thermal events. The photoluminescence (PL) spectrum of core‐shelled quantum dots (QDs) CdSe/ZnS irreversibly shifts with heating histories (temperature and duration) of thermal events. The induced PL shift of the QDs CdSe/ZnS is employed to permanently record thermal histories. We further model a kind of thermal history nanosensor based on the thermal‐induced phenomena of core‐shelled QDs to permanently record thermal histories at microscale and demonstrate to reconstruct temperature and duration of heating events simultaneously from PL spectra of the QDs. The physical mechanism of the sensors is discussed.     

Graphene Quantum Dots

Graphene quantum dots (GQDs) are nanometer‐sized fragments of graphene that show unique properties, which makes them interesting candidates for a whole range of new applications. This review article gives an overview of the synthesis, properties and applications of GQDs. Synthesis methods discussed include top‐down and bottom‐up approaches. Properties such as luminescence up‐ and down‐conversion have been used in applications ranging from energy conversion to bio‐analytics. This article provides an overview of the state‐of‐the‐art and highlights promising findings as well as potential future directions of the research field.     

Mn掺杂ZnSe量子点变温发光性质研究

量子点(QD)照明器件中电流导致的焦耳热会使其工作温度高于室温,因此研究量子点的发光热稳定性十分重要。本文利用稳态光谱和时间分辨光谱研究了具有不同壳层厚度的Mn掺杂ZnSe(Mn: ZnSe)量子点的变温发光性质,温度范围是80～500 K。实验结果表明,厚壳层(6.5单层(MLs))Mn: ZnSe量子点的发光热稳定性要优于薄壳层(2.6 MLs)的量子点。从80 K升温到400 K的过程中,厚壳层Mn: ZnSe量子点的发光几乎没有发生热猝灭,发光量子效率在400 K高温下依然可以达到60%。通过对比Mn: ZnSe量子点的变温发光强度与荧光寿命,对Mn: ZnSe量子点发光热猝灭机制进行了讨论。最后,为了研究Mn: ZnSe量子点的发光热猝灭是否为本征猝灭,对具有不同壳层厚度的Mn: ZnSe量子点进行了加热-冷却循环(300-500-300 K)测试,发现厚壳层的Mn: ZnSe量子点的发光在循环中基本可逆。因此,Mn: ZnSe量子点可以适用于照明器件,即使器件中会出现不可避免的较强热效应。