Synthesis And Photoluminescent Properties Of Core/Shell Structure ZnS: Mn Nanocrystals

In the nanomaterials science, a great deal of effort has been devoted to the semiconductor nanomarials. Research onâ…¡-â…¥semiconductor materials is a hotspot nowadays, especially in their optical and electric properties. As a kind of luminescent materials, Mn-doped ZnS nanocrystal has drown considerable interests because of its broad potential application prospect, and the luminescent mechanism, preparation method and practical application have been researched deeply. But the surface states usually act as luminescence quenching centers, causing low luminescent efficiency. There is a large distance for Mn-doped ZnS nanocrystal to application, which was mainly caused by the surface states. Hence, the modification of surface is of crucial importance for the applications of this type of luminescent semiconductor nanomaterials. Among all the surface modification methods, core/shell structure is proved to be a very effective method. This paper focuses on the impact of inorganic shell on luminescent properties of Mn-doped ZnS nanocrystals, which aimed at improving the luminescence efficiency by diminishing or eliminating the surface states. The main work of this paper is listed as follows:1. Mn-doped ZnS spherical nanoparticles and nanorods were synthesized by solvothermal. It was found that the morphology of nanocrystals can be controlled by changing the mole raito of Zn and S, keeping the ethylenediamine and water in 1:1 volume ratio severing as solvent. When the mole ratio of Zn and S was 2:1, spherical nanoparticles were obtained; when the mole ratio of Zn and S was 1:1, nanorods were obtained;2. Core/shell structure ZnS:Mn/ZnS,ZnS:Mn/CdS,ZnS:Mn/ZnO,ZnS:Mn/SiO2 nanoparticles and ZnS:Mn/ZnS nanorods with different shell thicknesses were synthesized. The samples were characterized by TEM, XRD, XPS, PL and PLE. TEM and XPS measurements showed the evidence for the core/shell structure. PL and PLE spectra showed the shell with appropriate thickness can enhance the photoluminescence intensity of ZnS:Mn nanomaterials; at the same time, some kinds of shell materials can bring strain on the ZnS:Mn core, inducing the red shift in PLE spectra. The details are as follows:(1) As the ZnS shell thickened, the Mn emission intensity of ZnS:Mn/ZnS nanoparticles showed an increase followed by a steady decline, which attained its maxium at 0.05 shell thickness. The PLE spectra showed a gradual red shift with ZnS shell thickening.(2) As the CdS shell thickened, the Mn emission intensity of ZnS:Mn/CdS nanoparticles showed a gradual decline. In the PLE spectra, the peak position of ZnS exhibited a progressive blue shift, and the absorbtion of ZnCdS in alloy state can also be observed.(3) As the ZnO shell thickened, the Mn emission intensity of ZnS:Mn/ZnO nanoparticles showed an increase followed by a steady decline, which attained its maxium at 0.1 shell thickness. The PLE spectra showed an obvious blue shift after coating ZnS:Mn nanoparticles with ZnO.(4) As the SiO2 shell thickened, the Mn emission intensity of ZnS:Mn/SiO2 nanoparticles showed an increase followed by a steady decline, which attained its maxium at 5 shell thickness. The PLE spectra showed a same degree of blue shift after coating ZnS:Mn nanoparticles by SiO2 shells of differents.(5) As the ZnS shell thickened, the Mn emission intensity of ZnS:Mn/ZnS nanorods showed an increase followed by a steady decline, which attained its maxium at 0.1 shell thickness. The peak position of PLE spectra kept almost unchaged after coating ZnS:Mn nanorods with ZnS.