Preparation And Characterization Of ZnO And ZnO/SiO₂ Core-shell Structure Quantum Dot

Quantum dots?QDs?,also known as nanocrystals,are very popular new semiconductor materials in recent years.QDs have a wide and continuous excitation spectrum,narrow and symmetric emission spectra,strong photoresistance and other fluorescent characteristics,and are widely used in light-emitting diodes?LEDs?and QD-sensitized solar cells?QDSSC?.At present,the most studied materials in the field of QDs are Cd Se,Cd Te,In P,etc.Although the process development for these materials is relatively mature,the most widely used.However,such materials themselves are highly toxic,which limits the further application of such QDs.ZnO QDs have the advantages of being non-toxic and harmless,and low living body rejection,which can effectively avoid the defects of traditional quantum dots.In this thesis,ZnO QDs with core-shell structure were synthesized by ultrasonic-assisted chemical method in liquid phase,and their structure and optical properties were characterized and analyzed.The main work of this article includes the following:?1?A quantum dot synthesis method with incompletely dissolved solutes was developed.ZnO QDs were synthesized at room temperature using zinc acetate as the zinc source in the ethanol system.The structure and fluorescence properties of ZnO QDs synthesized under different conditions?reaction time,reaction temperature,reactant ratio,stabilizer,etc.?were studied in detail.The experimental results show that the ZnO QDs prepared have the best properties when the molar ratio of the reactants is 1.2:1,the temperature is at 40°C,and the reaction takes 30minutes.At this time,the QDs have a uniform particle size?average particle size of 4.8 nm?,a high degree of monodispersity,and good crystallinity,and also have the highest fluorescence intensity and quantum yield.The comparison between 365nm UV lamp irradiation and CIE chromaticity diagram found that the prepared ZnO QDs emit soft fluorescence,which has the potential for application in the fields of biological detection and lighting.Due to the combined effects of size and surface effects,the stability of the synthesized quantum dots is not good,and agglomeration will occur after a period of time.?2?In order to overcome the adverse effects caused by quantum effects.an ultrasound-assisted chemical synthesis method was developed to carry out the core-shell coating experiment.We used3-aminopropyltriethoxysilane?APTES?to modify the surface of ZnO and coat it with silanization to prepare core-shell structured ZnO/SiO₂QDs.By changing the reaction conditions,the best data can be obtained.The experimental results show that the obtained sample has a core-shell structure,and the overall particle size is about 6 nm.Compared with pure ZnO QDs,the dispersion of quantum dots in the core-shell structure has been greatly improved.The absorption spectroscopy characterization shows that the coated ZnO QDs are protected from agglomeration and growth,and the sample has good stability.The core-shell quantum dots were transferred to the aqueous phase through phase transfer and it was found that there was still strong fluorescence emission without obvious agglomeration.It shows that the sample has good water stability.According to the fluorescence spectrum characterization,it can be seen that the fluorescence intensity of the core-shell structured ZnO QDs has been greatly improved,and the absolute quantum yield has also increased by about 17%.The sample has excellent optical properties.