The Organic Acid Decoration And Luminescent Mechanism Of Zno Quantum Dots

ZnO is an environmentally friendly oxide semiconductor and inexpensive luminescent material compared with traditionally used quantum dots (QDs) of CdSe or CdTe, which makes it more attractive for practical applications. However, the application is restrained by the low quantum yield of ZnO nanoparticles. Thus, many methods have been used to improve the luminescent properties of ZnO.In this work, chemical method has been used to synthesize ZnO quantum dots with green-light emission. After comparing ZnO quantum dots using different zinc salt, it is found that the ZnO quantum dots prepared by zinc chloride have the fine size and good luminescence. But it faces the problem of aggregation and low quantum yield (9.9%). Green emission of ZnO quantum dots is attributed to oxygen vacancy defects according to the results of UV-Vis absorption, luminescence and fluorescence lifetime.Organic acids with different structures, oleic acid(OA), propionic acid(PA), acrylic acid(AA), methyl acrylic acid(MAA), are selected to modified ZnO quantum dots. AA and MAA with rigid structures are found to enhance the light emission of ZnO quantum dots, while OA and PA with flexible chains reduce the emission intensity of ZnO quantum dots. And ZnO quantum dots modified by MAA have good dispersion and high quantum yield (25.8%).Through analysis of IR, PL, TRPL, UV-Vis absorbtion and the calculation on band structure, the mechansisms of organic acids affecting the luminescent intensity of ZnO quantum dots are explored. AA and MAA improve the luminescence of ZnO quantum dots due to the rigid molecular chain which can effectively eliminate the non-radiative recombination on the surface of ZnO quantum dots. OA and PA decrease the luminescent intensity of ZnO quantum dots because their flexible molecular chains provide new paths of non-radiative recombination by molecular vibration and rotation.