| As the core industry in the field of electronic information,new display is one of the key development directions of our country’s strategic emerging industries.At present,new display technologies and products such as Mini/Micro-LED display and laser display have gradually entered the market,leading to the comprehensive development of display materials,devices and technologies.At the same time,the innovation of materials and technologies is the key to continuous breakthroughs in the new display field.As semiconductor nanomaterials,quantum dots(QDs)have excellent optical properties,such as wide absorption range,narrow emission half-peak width,large Stokes shift,etc.The biggest feature is that the crystal size is in the nanometer scale,which can confine the internal electrons in a small space,thereby obtaining a special electronic structure and adjustable energy level distribution,giving QDs high photoresponse performance,high luminous brightness,and pure color.,fast electron transfer and special chemical and physical functions,Therefore,QDs have been widely regarded as nano-semiconductor materials with great potential for next-generation display technology.However,the large specific surface area makes QDs have a large number of defect sites,which capture a large number of electrons generated from the excitation of QDs,breaking the original radiative recombination process of electron-hole pairs,resulting in the phenomenon of fluorescence quenching and reducing the luminous efficiency of QDs,in view of the inherent problems of the above QDs,this paper is based on cadmium selenide(Cd Se)QDs,using shell coating method and transition metal ion doping and other QDs surface modification techniques.The structure of QDs was analyzed and tested by Fourier transform infrared spectroscopy(FT-IR),transmission electron microscopy(TEM),X-ray diffraction(XRD)and other characterization methods,the luminescence properties and stability of QDs were evaluated by ultraviolet absorption spectroscopy(UV-Vis),fluorescence spectroscopy(PL)and other characterizations,and the optical properties(luminescence purity,brightness,quantum yield)of Cd Se QDs were comprehensively improved.The specific research contents of this paper are as follows:(1)Preparation and optical properties of double-shell-coated QDsUsing pre-prepared selenium,sulfur,zinc,and cadmium precursor solutions,a series of core-shell QDs were prepared by thermal injection method to continuously epitaxially grow Zn Cd Se alloy shell and Zn S shell on Cd Se QDs,and the luminescence properties of these QDs were investigated.The research shows that: due to the coating of the alloy shell Zn Cd Se,the recombination luminescence process of electrons and holes is controlled at the core-shell interface,which reduces the capture of electrons by defects and increases the PLQY to 60.31%;The coating of Zn S shell blocked the contact between QDs and water and oxygen,improved the stability of QDs,and further increased the PLQY to 66.52%,0.25 mmol of cadmium in the alloy shell achieves the most matched lattice structure of the shell material,which reflects the narrowest halfpeak width and the longest fluorescence lifetime.In addition,short-chain ligands(halide ions,mercaptopropionic acid)replace the unstable oleic acid ligands on the periphery of QDs,quickly occupy the surface defects of QDs,and reduce fluorescence quenching.Among them,the best PLQY of 77.65% was obtained with halide ions as ligands.(2)"One-pot" preparation and luminescent properties of gradient shell QDsAn improved "one-pot method",namely a one-shot injection method,was used to inject the Se-S precursor solution into the reaction solution at high temperature.After the synthesis of Cd Se QDs,the gradient Zn Cd Se S shell layer was coated on the periphery using the reaction selectivity sequence,a series of green QDs with gradient shell structures were prepared by varying different ratios of Zn/Cd and Se/S.The results of luminescence performance studies show that compared with multi-shell QDs,the gradient shell has a complex elemental composition and a denser structure,and the improved experimental method avoids the possibility of QDs contacting the outside world,ensuring the purity of the synthesis process,and the PLQY reaches 69%.When the Se/S ratio is 0.15:0.85,the half-width of QDs decreases below 30 nm,and the Zn/Cd ratio determines the compactness of the shell material structure,that is,the passivation ability of the surface defects of QDs,when the Zn/Cd ratio is 0.09:0.81,the PLQY reaches 79.33%,and the decrease of the fluorescence intensity is only 1.01%.(3)Transition metal induced effect to improve the luminescence properties of QDsBased on the principle of ion doping,pre-prepared transition metal ion precursors were injected into the reaction system by solvothermal method to form new gradient shell QDs of Cd Se/(M)Zn Cd Se S,the inductive effect of transition metal on the electrons in the core accelerates the transfer of electrons in the QDs,making the consistent luminescence process of electron-hole pairs more likely to appear at the coreshell interface.In addition,the doping of a small amount of transition metal ions makes up for the problem of Zn being oxidized in the shell material,avoiding the problem of additionally generating new defects.Among them,the PLQY of Cd Se/(Co)Zn Cd Se S QDs achieved 83%,and the environmental stability was further improved. |
