Aqueous Synthesis And Luminescence Propetries Of CdS And CdTe Semiconducting Nanocrystals

Semiconductor nanocrystals (NCs) have attracted much attention in recent years, because theirquantum size effect, quantum confinement effect and good fluorescence efficiency. II-VI semiconductornanocrystals, have received enormous attention because their size-dependent electronic and opticalproperties, making them potential candidates for various technological applications, such aslight-emitting diodes, lasers, solar cell and biological labels.Although the organometallic syntheticism open up the possibility of realizing specifc advantages ofNCs, e.g., quantum confnement and resistance to photooxidation, the synthesized way is toxicitybecause heavy use of TOPO, Cd (CH3)2, TOP, ODE, and other highly toxic expensive chemical reagents.In this paper, the NCs was synthetized bu a new green synthesized way.Firstly, CdS:Ag NCs which has uniform size, excellent optical properties was synthesized bymicrowave-assistant procedures. As the Ag ions doped, the spectra of fluorescence emission covered theregion from visible to near infrared. In this method, the thiourea as the sulfur source, the3-mercaptopropionic acid (MPA) as the surfactant. Thiourea is a low cost, environmental friendly sulfursource. The experimental procedure is very simple. These factors make the whole reaction accord withgreen chemistry and energy saving principles of chemistry. In this article, the effects of temperature andreaction time on the NCs size, UV absorption and fluorescence emission properties are studied. Usingenergy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) analysed samplesof the element composition, the valence of doped Ag ions in the NCs coexist with+1and+2, and thedopant ions’ valence and the dopant position were influenced on the microwave reaction temperature.Using X-ray powder diffraction(XRD), transmission electron microscopy (TEM), fluorescencespectroscopy (PL), liquid UV-visible absorption spectroscopy (UV-vis) to character the size,fluorescence properties and UV absorption properties, solution stability and light stability of CdS:AgNCs. By adjusted and optimized these factors control the fluorescence properties of the CdS NCs.Secondly, CdTe NCs is synthesized under high-pressure condition. Compared with ordinaryconditions samples, the pressure has affected the structural of NCs and fluorescence properties. As pressure samples have much more redshift than atmospheric samples, it proved that the pressure iscontribute to the growth of the NCs. As the pressure increased, the redshift value of fluorescenceemission peak decreases. In the early time of the NCs growth, it much faster than ordinary conditionsones. But as time extension, NCs growth speed slow down gradually under the high pressure condition.The pressure condition works on the stage of nucleation and growth of crystal growth stagerespectively. The fluorescence analysis deduced the stress has important influence to the crystal structureand fluorescence properties in the crystal nucleation stage.