Synthesis And Luminescence Properties Of Ions Doped ZnS Nanocrystals

Semiconductor nanocrystals have being used widely in many fields bacause of unique optical and electrical properties, especially in the immunobiology and clinical inspection applications, etc. Now, QDs are used as biological markers which mainly contained cadmic, such as CdSe, CdS, CdSe/Zn S(ZnSe), CdTe/CdS/ZnS which is toxic to human health. Zinc sulfide(ZnS) is an important II-VI semiconductor material and it is a good doping host with a wide forbidden band. ZnS is expected to be uesd as a new high sensitive fluorescent marker because it can emit different wavelenth and high efficiency fluorescence by ion doping.In this work, ZnS nanocrystals with different doping ions were synthesised by hydrothermal method with 1-ethyl-3-methylimidazolium ionic liquid and water mixture as the reaction solvent. Phase, structure and morphology of the samples were analyzed by XRD, XPS and TEM techniques. Optical properties were determined by F-280 fluorescence photometer and Zolix SBP-300 grating spectrometer. The results of the study are as follows:1. ZnS: Cu, ZnS: Cu/Fe, Zn S: Er, ZnS: Er/Yb nanocrystals are about 3-10 nm in size and have a cubic zinc blende crystal structure, which have a small amount of agglomerate phenomena. It can be informed that nanocrystals are of polycrystalline structure by selected-area electron diffraction(SAED) analyses.2. The doped ions of ZnS nanocrystals exists in these states: Cu+/Cu2+, Fe2+, Er3+ and Yb3+. Fe-doped ions increased Cu2+ content in ZnS nanocrystals. Yb-doped ions increased Er3+ content in Zn S nanocrystals.3. There are two strong emission peaks at 425 nm and 468 nm. ZnS: Cu nanocrystals have the strongest performance with Cu ions doping at amount of 2% at 200?C. When Fe ions doped in ZnS: Cu nanocrystals, the fluorescence peak intensity of nanocrystals increases. Zn S: Cu/Fe nanocrystals have the strongest performance with the Fe ions doping at amount of 2% for 10 h reaction time at 140?C.4. ZnS: Er nanocrystals have three strong emission peaks at 420 nm, 470 nm and 530 nm. Zn S nanocrystals with Er-doping at amout of 2% have the maximum intensity of photoluminescence for 10 h reaction time at 120?C. ZnS: Er/Yb nanocrystals have the strongest performance with the Er/Yb ions doping at amount of 2% for 8h and 10 h reaction time at 140?C.5. ZnS: Er/Yb nanocrystals were excited by 980 nm, 200 mW laser. The electrons of up-conversion luminescence were observed in the 4f-4f orbit. There are two fluorescence peaks at 540nm(green) and 655nm(orange red).In this work, Zn S nanocrystals with different doping ions were synthesized without cadmium. The excitation and emission wavelengths of Zn S nanocrystals could be adjusted. They are expected to be applied in the field of light emitting devices and biological markers.