Tunable and High Photoluminescence Quantum Yield from Self‐Decorated TiO2 Quantum Dots on Fluorine Doped Mesoporous TiO2 Flowers by Rapid Thermal Annealing

Herein a novel approach is reported to achieve tunable and high photoluminescence (PL) quantum yield (QY) from the self‐grown spherical TiO₂ quantum dots (QDs) on fluorine doped TiO₂ (F‐TiO₂) flowers, mesoporous in nature, synthesized by a simple solvothermal process. The strong PL emission from F‐TiO₂ QDs centered at ≈485 nm is associated with shallow and deep traps, and a record high PL QY of ≈5.76% is measured at room temperature. Size distribution and doping of F‐TiO₂ nanocrystals (NCs) are successfully tuned by simply varying the HF concentration during synthesis. During the post‐growth rapid thermal annealing (RTA) under vacuum, the arbitrary shaped F‐TiO₂ NCs transform into spherical QDs with smaller sizes and it shows dramatic enhancement (≈163 times) in the PL intensity. Electron spin resonance (ESR) and X‐ray photoelectron spectroscopy (XPS) confirm the high density of oxygen vacancy defects on the surface of TiO₂ NCs. Confocal fluorescence microscopy imaging shows bright whitish emission from the F‐TiO₂ QDs. Low temperature and time resolved PL studies reveal that the ultrafast radiative recombination in the TiO₂ QDs results in highly efficient PL emission. A highly stable, biologically inert, and highly fluorescent TiO₂ QDs/flowers without any capping agent demonstrated here is significant for emerging applications in bioimaging, energy, and environmental cleaning.     

后退火对InxGa1—xAs单层量子点光学性质的影响

研究了以ＧａＡｓ和Ａｌ０．１５Ｇａ０．８５Ａｓ为基体,当铟的摩尔分数（ｘ）不同时,后退火对ＩｎｘＧａ１－ｘＡｓ单层量子点光致荧光（ＰＬ）谱特性的影响。后退火将导致铟含量不同的样品（ｘ＝０．２３,０．３７,０．５０,１．０）的ＰＬ谱线宽度变窄和蓝移。对于ＧａＡｓ基体,在７００℃退火９０分钟所造成的ＰＬ谱蓝移与退火３０分钟相似;（仅当ｘ＝０．２３时,退火９０分钟所造成的ＰＬ谱蓝移小于３０分钟）。对于Ａｌ０．１５Ｇａ０．８５Ａｓ基体,在７００℃退火３０分钟和９０分钟,其ＰＬ谱蓝移是不同的。     

低维MoS_2混合纳米片的发光特性

采用液相剥离法剥离MoS2块体材料,通过选择合适的剥离剂、超声时间、超声功率得到含有不同尺寸且分散均匀的MoS2混合纳米薄片悬浮溶液。在360 nm光激发下,这种悬浮液表现出单层MoS2及小尺寸MoS2纳米颗粒的复合发光特征。与微机械剥离得到的单层MoS2的发光特性相比,这种液相法得到的混合纳米薄片在512 nm处的最强发光峰位发生明显蓝移。混合纳米薄片在横向尺度上所产生的量子限制效应可能是导致该峰位蓝移的主要原因。     

Water‐Soluble Monolayer Molybdenum Disulfide Quantum Dots with Upconversion Fluorescence

Uniform water‐soluble monolayer MoS₂ quantum dots (MQDs) with lateral sizes of ≈2.1 nm, a clearly zigzag‐terminated edge, and a hexagonal lattice structure are achieved using ammonium molybdate, thiourea, and N‐acetyl‐l ‐cysteine (NAC) as precursors and the capping reagent in a facile one‐pot hydrothermal approach. MQDs have good dispersity and high stability in aqueous suspension and exhibit a significantly larger direct bandgap (3.96 eV) compared to monolayer MoS₂ nanosheets (1.89 eV). Pronounced blue‐shifts in the wavelengths of both the excitonic absorption and intrinsic state emission with activated strong luminescence at room temperature beyond monolayer MoS₂ nanosheets is demonstrated. Unusual upconversion photoluminescence is also observed and is caused by two successive transfers of energy from the near‐infrared (NIR) absorption generated by the NAC capping reagent to the hexagonal structure of MQDs. Additional optical properties of MQDs may provide numerous exciting technological applications. Here, MQDs are demonstrated as a highly selective fluorescent reagent for detecting tetracycline hydrochloride under UV and NIR irradiation.     

退火对CdSe量子点荧光影响的色度学研究

制备出两种尺寸的CdSe量子点.结合色度学分析,比较了固化在PMMA基质中两种尺寸CdSe量子点在退火中发生的不同变化以及相应光谱颜色的改变.小尺寸CdSe量子点在退火中有团聚的趋势,退火后荧光明显红移,如果退火温度超过一定范围,会产生显著的双尺寸分布效应,对应的色度坐标有从白光区域向上移动到绿色区域的趋势.较大尺寸的CdSe量子点,其热稳定性相对更好,退火造成荧光红移,对应绿色区域中的色度坐标有向右移动的趋势,但颜色改变不明显,因此更适合于发光显示方面的应用.     

基于InP/ZnS核壳结构量子点的色转换层设计及制作

提出了采用环境友好型InP/ZnS核壳结构量子点材料制备匹配蓝光Micro-LED阵列的量子点色转换层以实现Micro-LED阵列器件全彩化的技术方案。通过采用倒置式量子点色转换层方案,实现了InP/ZnS量子点材料和Micro-LED阵列的非直接接触,从而可以缓解LED中热量聚集导致的量子点材料发光主波长偏移、半峰宽展宽以及发光效率衰减等问题。量子点色转换层中内嵌PDMS聚合物柔性膜层,可以消除咖啡环效应,同时,色转换层中内嵌飞秒激光图案化处理的500 nm长波通滤光膜层,可以抑制蓝光从非蓝色像素单元出射。最后,实验制备了像素单元中心间距90μm的16×16 InP/ZnS量子点色转换层。该设计可以实现基于蓝光Micro-LED阵列的全彩色Micro-LED显示器件的制备,并且该制备方法可以降低全彩色Micro-LED阵列显示器件的制备成本。     

Size‐Dependent Structural and Optical Characteristics of Glucose‐Derived Graphene Quantum Dots

It is of scientific importance to obtain graphene quantum dots (GQDs) with narrow‐size distribution in order to unveil their size‐dependent structural and optical properties, thereby further to explore the energy band diagram of GQDs. Here, a soft‐template microwave‐assisted hydrothermal method to prepare GQDs with diameters less than 5 nm ± 0.55 nm is reported. The size‐dependent photoluminescence (PL) quantum yield (QY) decay lifetime and electron energy loss spectroscopy (EELS) of the GQDs are studied systematically. The QY of the GQDs with an average diameter of 2 nm is the highest (15%) among all the samples investigated and the QY decreases with increasing diameter of the GQDs. The size‐dependence of the PL decay lifetime is also observed. The result suggests that spatial confinement effects related to radiative relaxation play an important role in the size‐dependent decay lifetime. A realistic energy band diagram of the GQDs is deduced from the experimental results.     

CsPbBrI2量子点制备及其光探测器性能

采用热注入法制备空气稳定性良好的CsPbBrI2量子点,以375 nm的脉冲激光作为激发光源研究其光致发光性能.通过旋涂的方式制备相应薄膜,将其作为光敏层应用到光探测器,并对器件的光电子性能和稳定性进行详细研究.结果表明:CsPbBrI2量子点在635nm附近有强烈的荧光效应,光谱发光峰较窄,半峰宽约为35 nm.CsPbBrI2量子点禁带宽度为1.90eV,制备的探测器光检测带宽从紫外光260nm到红光650 nm,光响应度为0.26 A/W,高开/关比高达104,上升/衰减时间为3.5 ms/3.5 ms.在25℃,湿度在25%~35%大气环境下存储60天,性能与初始值相比几乎没有变化.CsPbBrI2量子点具有优异的稳定性、可制备高性能的宽带光检测和易于制造等优点,具备一定的应用前景.     

Ti~+离子注入结合热退火法制备TiO_2纳米薄膜研究

利用金属蒸发真空多弧离子源(MEVVA源)注入机将Ti+离子注入到高纯石英玻璃衬底中,离子注入的加速电压为20 k V,注入剂量为1.5×1017和3×1017ions/cm2,将注入样品在氧气气氛下进行热退火处理,制备了TiO2纳米薄膜。采用光吸收谱、拉曼光谱、X射线光电子能谱、扫描电子显微镜和透射电子显微镜对注入样品进行了测试和表征,分析了TiO2薄膜的形成机理。在热退火过程中衬底中离子注入的Ti原子向外扩散到衬底表面被氧化形成了TiO2。TiO2的形成、晶粒尺寸和晶体结构依赖于热退火温度,而形成TiO2薄膜的厚度主要受离子注入剂量和热退火时间的影响。实验结果表明,该方法制备的TiO2纳米薄膜将有望应用于制备具有光催化、自清洁等特殊性能的自清洁玻璃。     

壳聚糖包裹AgInS_2的物理表征及生物毒性研究

选用天然多糖中唯一的碱性多糖——壳聚糖作为稳定剂和包裹剂,成功合成了水溶性的Ag In S2量子点/低分子量壳聚糖纳米复合材料(Ag In S2/LCSMS)。利用透射电子显微镜(TEM)、FT-IR傅里叶红外光谱仪、紫外吸收光谱、荧光分光光度计等表征手段对纳米复合材料的形貌、化学组成及光学性质进行了研究。结果表明,Ag In S2/LCSMS纳米复合材料的粒径约为5~6 nm,在水相中仍具有较稳定的发光。之后,对Ag In S2/LCSMS纳米复合材料的生物相容性进行了研究,对比Ag In S2/LCSMS纳米复合材料与Ag In S2量子点的细胞活性测试结果发现,Ag In S2/LCSMS纳米复合材料的细胞活性比Ag In S2量子点有了明显的提高,说明通过低分子量壳聚糖的包裹可以明显提高纳米材料的生物相容性。因此,这类具有较好水溶性和生物相容性的荧光Ag In S2/LCSMS纳米复合材料可作为优良的生物荧光标记材料在生物医学检验、细胞以及活体成像研究中有广泛的应用前景。     

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.     

Hydrothermal Preparation of Photoluminescent Graphene Quantum Dots Characterized Excitation‐Independent Emission and its Application as a Bioimaging Reagent

Zero‐dimensional photoluminescent (PL) graphene quantum dots (GQDs) that can be used as the cell‐imaging reagent are prepared by a hydrothermal route using the graphene oxide (GO) as the carbon source. Under the optimized hydrothermal conditions, an initial hydrogen peroxide concentration of 0.5 mg mL^?1 at 180 °C for 120 min, the GO sheets can be cut into nanocrystals with lateral dimensions in the range of 1.5–5.5 nm and an average thickness of around 1.1 nm. The as‐prepared GQDs exhibit an abundance of hydrophilic hydroxy and carboxyl groups and emit bright blue luminescence with up‐conversion properties in a water solution at neutral pH. Most interestingly, they indicate excitation‐independent emission characteristics, and the surface state is demonstrated to have a key role in the PL properties. The fluorescence quantum yield of the GQDs is tested to be around 6.99% using quinine sulfate as a standard. In addition, the as‐prepared GQDs can enter into HeLa cells easily as a fluorescent imaging reagent without any further functionalization, indicating they are aqueous stability, biocompatibility, and promising for potential applications in biolabeling and solution state optoelectronics.     

脉冲溅射功率对含硅量子点SiC_x薄膜的结构和光学特性的影响

采用射频和脉冲磁控共溅射法并结合快速光热退火法制备了含硅量子点的SiC_x薄膜.采用掠入射X射线衍射、喇曼光谱、紫外-可见-近红外分光光度计和透射电子显微镜对薄膜进行表征.研究了脉冲溅射功率对薄膜中硅量子点数量、尺寸、晶化率和薄膜光学带隙的影响.结果表明:当溅射功率从70 W增至100 W时,硅量子点数量增多,尺寸增至5.33nm,晶化率增至68.67%,而光学带隙则减至1.62eV;随着溅射功率进一步增至110 W时,硅量子点数量减少,尺寸减至5.12nm,晶化率降至55.13%,而光学带隙却增至2.23eV.在本实验条件下,最佳溅射功率为100 W.     

Effect of temperature–bias annealing on the hysteresis and subthreshold behavior of multilayer MoS2 transistors

The transfer characteristics (I_D–V_G) of multilayers MoS₂ transistors with a SiO₂/Si backgate and Ni source/drain contacts have been measured on as‐prepared devices and after annealing at different temperatures (T_ann from 150 °C to 200 °C) under a positive bias ramp (V_G from 0 V to +20 V). Larger T_ann resulted in a reduced hysteresis of the I_D–V_G curves (from ～11 V in the as‐prepared sample to ～2.5 V after T_ann at 200 °C). The field effect mobility (～30 cm² V^–1 s^–1) remained almost unchanged after the annealing. On the contrary, the subthreshold characteristics changed from the common n‐type behaviour in the as‐prepared device to the appearance of a low current hole inversion branch after annealing. This latter effect indicates a modification of the Ni/MoS₂ contact that can be explained by the formation of a low density of regions with reduced Schottky barrier height (SBH) for holes embedded in a background with low SBH for electrons. Furthermore, a temperature dependent analysis of the subthreshold characteristics revealed a reduction of the interface traps density from ～9 × 10¹¹ eV^–1cm^–2in the as‐prepared device to ～2 × 10¹¹ eV^–1cm^–2after the 200 °C temperature–bias annealing, which is consistent with the observed hysteresis reduction.

Schematic representation of a back‐gated multilayer MoS₂ field effect transistor (left) and transfer characteristics (right) measured at 25 °C on an as‐prepared device and after the temperature–bias annealing at 200 °C under a positive gate bias ramp from 0 V to +20 V.     

CdTe量子点功能化玻片的制备及其对Pb2+浓度的检测

通过羟基化和氨基硅烷化处理,得到表面接枝氨基的玻片载体。水相合成巯基乙酸修饰的CdTe量子点(CdTe-TGA),采用EDC/NHS活化反应,将量子点偶联到氨基化玻片表面,制备出具有荧光性能的功能化玻片。考察了量子点与EDC的量比、活化时间、偶联温度以及偶联时间对偶联效果的影响。结果表明,在量子点与EDC的量比为1:30、活化时间1 h、偶联温度30 ℃、偶联时间4 h条件下获得的功能化玻片具有最佳的荧光性能。将该条件下制备的功能化玻片用于水溶液中Pb²⁺的浓度检测,得到玻片相对荧光猝灭强度随Pb²⁺浓度变化的线性曲线,线性范围为1.0×10^-9~4.0×10^-8mol·L^-1,检出限为3.8×10^-9mol·L^-1,且具有良好的选择性。该方法可以灵敏而准确地检测Pb²⁺浓度。