Preparation,Characterization And Properties Of ZnSe:Ag/ZnS/SiO₂-NH₂ And ZnSe:Co/ZnSe/ZnS Fluorescent Nanoparticles

?-?group semiconductor fluorescent quantum dots,as a new type of fluorescent labeling material,have attracted wide attention becuase of their unique photoelectric properties and good application prospects in the field of biological analysis.ZnSe quantum dots have low toxicity and excellent fluorescence performance,which has become one of the research hotspots today.The synthesis of water-soluble ZnSe core quantum dots doped with different kinds of transition metals(such as Fe³⁺,Mn²⁺,Cu²⁺,Co²⁺,Ni²⁺,Ag⁺)has been extensively reported,but such quantum dots have disadvantages such as low fluorescence quantum yield and poor stability,which hinder their practical application.After being coated with an inorganic shell layer such as ZnSe and ZnS,the fluorescence quantum yield and stability of the transition metal ions doped water-soluble ZnSe core-shell quantum dots are improved.But for practical applications in complex physiological environments,its surface modifier molecules and shell layer are easy to slowly fall off,resulting in fluorescence reduction or even quenching.Based on the above problems,it is of great significance to further improve the fluorescence quantum yield and stability of quantum dots.This paper mainly focuses on two aspects:one is the preparation and characterization of ZnSe:Ag/ZnS/SiO₂-NH₂nanoparticles and ZnSe:Co/ZnSe/ZnS core/shell/shell quantum dots with improved fluorescence quantum yield and stability;the other is the detailed study on the stability of the synthesized products.(1)L-cysteine-modified water-soluble ZnSe:Ag/ZnS core/shell quantum dots were successfully prepared.The structure,morphology,component as well as optical properties of the obtained products have been characterized through X-ray power diffraction,energy dispersive X-ray spectrum,transmission electron microscopy,infrared spectrum,ultraviolet-visible spectrum,and fluorescence spectrum.The results indicate that ZnSe:Ag/ZnS quantum dots have a cubic zinc blende structure,exhibit spherical shape with good dispersity,and most of the particle size is about 3.7 nm.Using quinine sulfate as the reference,the fluorescence quantum yield of ZnSe:Ag/ZnS core/shell quantum dots measured can reach up to 13%.The resistance of ZnSe:Ag/ZnS core/shell quantum dots to ultraviolet radiation,p H buffer solution,Na Cl solution and H₂O₂solution was investigated in detail.Compared with ZnSe:Ag core quantum dots,the stability of ZnSe:Ag/ZnS core/shell quantum dots is significantly enhanced.(2)Amino-modified ZnSe:Ag/ZnS/SiO₂ nanoparticles were prepared by St(?)ber method.The products have been characterized through X-ray power diffraction,energy dispersive X-ray spectrum,transmission electron microscopy,infrared spectrum,ultraviolet-visible spectrum,Zeta potential and fluorescence spectrum.The results show that the synthesized ZnSe:Ag/ZnS/SiO₂-NH₂nanoparticles are nearly spherical shape,each nanoparticle is coated with multiple fluorescent quantum dots,and most of the nanoparticles have a particle size between 20 and 70 nm.The effects of several synthesis conditions on the fluorescence properties of the as-prepared ZnSe:Ag/ZnS/SiO₂-NH₂nanoparticles are surveyed and the optimum synthesis conditions are found to be as follows:reaction temperature of 35°C,reaction time of 12 hours,ammonia water of 120?L,quantum dots solution of 10 m L,TEOS solution of 6?L,APTES solution of 15?L.Using quinine sulfate as the reference,the fluorescence quantum yields of ZnSe:Ag/ZnS/SiO₂nanoparticles and ZnSe:Ag/ZnS/SiO₂-NH₂nanoparticles were measured to be 17%and 15%,respectively.The resistance of ZnSe:Ag/ZnS/SiO₂-NH₂ nanoparticles to ultraviolet radiation,p H buffer solution,Na Cl solution and H₂O₂solution was investigated in detail.Compared with ZnSe:Ag/ZnS quantum dots,the photochemical stability of ZnSe:Ag/ZnS/SiO₂-NH₂nanoparticles is obviously improved.(3)L-cysteine-modified water-soluble ZnSe:Co/ZnSe/ZnS core/shell/shell quantum dots were prepared by epitaxial growth method.The structure,morphology,component as well as optical properties of the obtained products have been characterized through X-ray power diffraction,energy dispersive X-ray spectrum,transmission electron microscopy,infrared spectrum,ultraviolet-visible spectrum,and fluorescence spectrum.The results indicate that ZnSe:Co/ZnSe/ZnS core/shell/shell quantum dots have a cubic zinc blende structure,exhibit spherical shape with good dispersity,and most of the particle size is about 3.6 nm.The effect of ZnS shell thickness on the fluorescence properties of ZnSe:Co/ZnSe/ZnS core/shell/shell quantum dots was studied.The optimal molar ratio of n(ZnSe:Co/ZnSe)to n(ZnS)was 1:0.2.By coating the ZnS shell,the quantum yield of the prepared quantum dots increased from 15%to 21%.The resistance of ZnSe:Co/ZnSe/ZnS core/shell/shell quantum dots to p H buffer solution,Na Cl solution and H₂O₂solution was investigated in detail.Compared with ZnSe:Co/ZnSe core/shell quantum dots,the stability of ZnSe:Co/ZnSe/ZnS core/shell/shell quantum dots is obviously improved.