| Since the 1980 s,energy shortage has gradually become a global problem to be solved.Distribution of energy has become an important factor which limited the development of many less developed countries.According to the department of Energy,20% of global energy consumption is used to meet the lighting needs of daily life.As the second largest application export of energy consumption,it is necessary for China to deploy new lighting materials,develop new lighting technologies,and improve the efficiency of artificial light sources.As a new type of luminescent material,QDs have been used as luminescent layers in WLED fabrication.Due to its special size effect,QDs-based WLED have the advantages of high quantum yield,high color rendering index,long service life,low cost,and simple processing technology,so they have broad development prospects.At present,many mature quantum dot materials are used in WLED,most of which are II-VI semiconductor QDs containing Cd,such as CdSe and CdZnSe.However,Cd is a chronic toxin and carcinogen,and it is harmful for humans and the environment.In this paper,we aim to develop new and efficient Cd-free alternative materials to further promote the practical application of QDs and WLEDs.In the second chapter,we realized the room temperature dissolution of Se powder with a mixed solution of alkyl mercaptan and oleylamine to prepare a highly reactive Se precursor solution.The inorganic Zn salt is dissolved in a mixed solution of oleylamine and octadecene as a metal precursor solution.By using of the difference in reactivity between these precursors,defects are introduced into the ZnSe QDs.Then we coated the ZnSe QDs with the ZnS shell,and the fluorescence quantum yield of the ZnSe/ZnSe QDs was significantly improved.On the fluorescence spectrum,it shows a significant increase in the intensity of the fluorescent peak in the defect state.And the DFT calculations show that the defects in the ZnSe QDs are mainly vacancies inside the quantum dots and on the surface of the quantum dots.The internal vacancies of Zn and Se could introduce a defect state energy level,resulting in a fluorescent emission of a defect state.The vacancies on the surface will bring about non-radiative transitions,which will reduce the quantum yield.The ZnS shell can effectively eliminate the Se vacancies on the surface of the quantum dots and improve the fluorescence quantum yield of the quantum dots.This method can effectively obtain ZnSe QDs with high fluorescence quantum yield,broaden the luminescence range of ZnSe QDs,and lay a foundation for the application of ZnSe QDs in WLED.In the third chapter,based on the preparation of ZnSe/ZnS QDs,the Mn:ZnSe/ZnS quantum dots were successfully prepared by changing the reaction materials and incorporating Mn into the ZnSe/ZnS QDs.The fluorescence emission of Mn:ZnSe/ZnS QDs was derived from band edge emission of ZnSe,defect state emission of ZnSe,and Mn-related fluorescence emission.With the fluorescence blending of several sources,the effect of white light emission of Mn:ZnSe/ZnS QDs can be achieved,and the highest fluorescence quantum yield can reach 86%.Through the analysis of the fluorescence intensity and fluorescence lifetime of Mn:ZnSe/ZnS QDs,we concluded that there was energy competition and energy transfer between the defect state energy level of ZnSe and the luminescence energy level associated with Mn.According to this energy level relationship,we have achieved precise control of the luminescence of Mn:ZnSe/ZnS QDs by changing the doping amount of Mn and the growth temperature of ZnSe QDs.Furthermore,with Mn:ZnSe/ZnS QDs as the color conversion layer,we have successfully prepared photoluminescent WLED,which have good luminescence effects and can adjust the white color temperature from cold to warm. |
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