발광체 용 무기 코어/쉘/쉘 나노크리스탈의 친환경 합성에 관한 연구

Abstract

The inorganic semiconductor nanocrytals have been well-known due to their good optical, luminescent properties and chemical-stability. More interestingly, doping with other transition metallic ions such as Mn, Ni, Co, Cu or lanthanide atoms (Ir, Y, Gd, Pr) into semiconductor crystals enhances the photoluminescence quantum yields. The color-tunable luminescent property of single core nanocrystals depends on their shape, band gap, and deep trap or surface trap, while luminescence of doped into core nanocrystals is due to their various doping ionic metal, shape, and dopant concentration. In this vein, manganese has been chosen to dope in ZnS single core or doped into the ZnS shell in order to tune the colors from yellow to red/orange emission, stabilize and increase the photoluminescence quantum yields. However, these core/doped shell or core/doped shell/shell nanocrystals were synthesized in organic solvent using metal-organic reagents that is less economic, uneasy and unfriendly environmental systems due to many by-products and wastes after reactions. In this research, we have found the facile and green synthetic method of ZnSe/ZnS:Mn/ZnS nanocrystals in aqueous phase. We also synthesized Mn2+ doped into ZnS single core (ZnS:Mn) in water in order to compare the luminescent property and photoluminescence quantum yields of ZnS:Mn and ZnSe/ZnS:Mn/ZnS core/doped shell/shell nanocrystals. Especially, we have found that the color-tunable luminescence and photoluminescence quantum yields of ZnSe/ZnS:Mn/ZnS core/doped shell/shell nanocrystals depend on the Mn2+ dopant concentration. The thin outer shell layer ZnS protects the Mn2+ ions migration to surrounding and reduces the self-quenching effect of Mn2+ in order to increase the photoluminescence quantum yield of core/doped shell/shell nanocrystals. These core/multi-shell nanocrystals were synthesized in aqueous media using 3-mercaptopropionic acid as a stabilizer or capping agent in one flask reaction system under three steps. The precursors are the acetate metal salts which are cost-effective and well-dissolved in water with suitable feeding concentration. This green synthetic method is reproductive, economic and available for future large scale production. The photoluminescence quantum yields are at a range of 20.0-59.7% related to the Mn2+ dopant concentrations and growth time or reaction time. The sizes of these core/doped shell/shell nanocrystals are tightly independent to amount of Mn2+ dopant. At the Mn2+ dopant at 11.1 to 50.0% relative to Zn of the first shell, the average size of ZnSe/ZnS:Mn/ZnS core/doped shell/shell nanocrystals are 5-7.4 (±0.2) nm. The particles sizes were detected by UV-absorption, dynamic light scattering, and TEM images. Although there are three layers of nanocrystals, the core/doped shell/shell nanocrystals are all cubic crystalline with zinc-blende structure tracked of by XRD measurement. The well doping of Mn into the ZnS nanocrystals of the first shell was detected by XPS and photoluminescence spectra. The color-tunable property from white, yellow to orange/red emission and reaction mechanism of as-prepared core/doped shell/shell nanocrystals are going to be explained in this research.