PREPARATION AND CHARACTERIZATION OF WATER-SOLUBLE NEAR-INFRARED EMITTING PbS QUANTUM DOTS

A new facile method for preparing water-soluble near-infrared （NIR）-emitting PbS quantum dots （QDs） is proposed by using N-acetyl-L-cysteine （NAC, a derivate of L-cysteine） as its stabilizer. The influence of the precursor Pb/S molar ratio, the Pb/NAC molar ratio, and the pH of original solution on optical properties is explored. Results show that aqueous PbS QDs with strong NIR fluorescence can be prepared and their photoluminescence emission peaks can be tuned from 895 nm to 970 nm. Studies indicate that such aqueous QDs have a potential application in biomedical imaging, especially in noninvasive in vivo fluorescence imaging. In addition, the resulting PbS QDs are further characterized by a transmission electron microscopy and X-ray diffraction analysis.

Synthesis of CdSe quantum dots via paraffin liquid and oleic acid

This paper reported an efficient and rapid method to produce highly monodispersed CdSe quantum dots (QDs), in which the traditional trioctylphosphine oxide (TOPO) was replaced by paraffin liquid as solvent and oleic acid as the reacting media. The experimental conditions and the properties of QDs had been studied in detail. The resulting samples were confirmed of uniform size distribution with transmission electronic microscopy (TEM), while UV-vis absorption and photoluminescence (PL) spectra clearly indicated that such synthesized QDs had good fluorescence properties.

PbSe quantum dots for an evanescent wave excited fiber amplifier

A novel quantum dots （QDs） optical fiber amplifier was proposed and demonstrated. It was fabricated by dipcoating the PbSe QDs doped sol onto the taper region of fiber coupler. The PbSe QDs was synthesized according to a colloidal method. A lower refractive index sol was also synthesized as the host of PbSe QDs. A standard single mode fiber was used to make the fusion tapered fiber coupler which had double input and output ports. With the simple structure, a signal and a pump can be injected into the amplifier and excite the PbSe QDs through evanescent wave. The experimental results indicated that the amplified light wave was observed at 1 550 nm wavelength with 980 nm .wavelength laser diode as pump.

Morphology and Optical Properties of Self-Assembled In_(0.5)Ga_(0.5)As Quantum Dots with Different Spacer Layer Thickness

Uncapped double stacked In0.5Ga0.5As quantum dots（QDs） with different spacer layer thicknesses were grown using metal-organic chemical vapour deposition（MOCVD）.The precursors used for the growth of the GaAs layer and In0.5Ga0.5As QDs were trimethylgallium（TMGa）,trimethylindium（TMIn）,and arsine（AsH3）.The morphology and optical properties of the self-assembled In0.5Ga0.5As QDs were investigated and characterized using atomic force microscopy（AFM） and photoluminescence（PL）.The AFM images revealed that the sizes of the dots on the topmost were not uniformly distributed.The average size of the dots fluctuated as the GaAs spacer layer thickness increased.A room temperature PL measurement was used to establish the quality and quantity of the stacked QDs.The PL peak position remained at 1148 nm for all samples of QDs;however,the PL intensity increased as spacer layer thickness increased.The structure of the spacer layer in the stacked QD affected the morphology of the topmost surface of the QDs.The PL measurement coherently reflected the AFM characterization,in which the strong PL spectra were caused by the uniformity and high density of the QDs.The surface morphology,structure,and optical properties of the stacked QDs are attributed to seed-layer（first layer） formation of dots and spacer layer structures.

Roles of glutathione and L-cysteine in the biomimetic green synthesis of CdSe quantum dots

Biological synthesis of quantum dots （QDs） as an environmental-friendly and facile preparation method has attracted increasing interests. However, it is difficult to distinguish the roles ofbio-thiols in QDs synthesis process because of the complex nature in organisms. In this work, the CdSe QDs synthesis conditions in organisms were reconstructed by using a simplified in vitro approach to uncover the roles of two small bio-thiols in the QDs formation. CdSe QDs were synthesized with glutathione （GSH） and L-cysteine （Cys） respectively. Compared with Cys at the same molar concentration, the CdSe QDs synthesized by GSH had a larger and broader particle size distribution with improved optical properties and crystal structure. Furthermore, quantum chemical calculations indicate that the stronger Cd^2＋ binding capacity ofGSH contributed a lot to the CdSe QDs formation despite ofthe greater capability Cys for selenite reduction. This work clearly demonstrates the different roles of small thiols in the Cd2^＋- stabilization in the environment and biomimetic QDs synthesis process.

Size-dependent optical properties of InGaN quantum dots in GaN nanowires grown by MBE

Quantum dots in nanowires （DINWs） are considered as important building blocks for novel nanoscale semiconductor optoelectronic devices. In this paper, pure axial heterojunction InGaN/GaN DINWs are grown by using plasma-assisted molecular beam epitaxy （PA-MBE） system. The InGaN quantum dots （QDs） are disk-like observed by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The diameter of QDs can be controlled by the growth conditions of nanowires （NWs）, while the thickness of QDs can be controlled by the growth time of lnGaN. Temperature-dependent photoluminescence （TDPL） measurements demonstrate that the PL peak of DINWs with small and uniform sizes shows a general red shift with increasing temperature. However, the PL peak of D1NWs with non-uniform sizes shows an abnormal blue shift with increasing temperature, which is due to different internal quantum efficiencies of the DINWs with different sizes.