Controlled Synthesis And Tunable Optical Properties Of Ag-In-S-Based Nanocrystals

The light-emitting semiconductor nanocrystal（or quantum dot）is a quasi-zero dimensional nanomaterial,which exhibits unique optical electronic properties due to its quantum confinement effect.Semiconductor nanocrystals,with tunable band gap,higher color purity,high quantum yields,and high stability,are widely used in light emitting diodes,sensors and biomedicine.Currently,the advanced cadmium-based nanocrystal for electroluminescent devices is limited in practical applications due to its large toxicity.The cadmium-free materials developed in recent years mainly include invocated,perovskite,I-III-VI group quantum dots.The I-III-VI group quantum dots have received more and more attention in photovoltaic devices because of its low toxicity and simple synthesis.Among them,the Ag-In-S-based semiconductor nanocrystals has an excellent luminescence properties,such as high tunable luminescence range,large absorption range,and high light-emitting quantum yield.At present,the study of Ag-in-S-based semiconductor nanocrystals is blooming,and the quaternary Ag-In-Zn-S system constructed by introducing Zn²⁺can further broaden the spectral adjustable range and improve photoluminescent quantum yield.However,the performance of the above electroluminescent devices（especially green light devices）needs to be further improved.In addition,traditional I-III-VI semiconductor nanocrystals have a large number of defects,resulting in a wide full width at half maximum（FWHM）in their photoluminescence spectra.However,Ag-In-S-based semiconductor nanocrystals exhibit narrow band luminescence properties under specific synthesis strategies,which improve the color purity of conventional I-III-VI semiconductor nanocrystals.Based on the above research background,this paper first regulates components of the quaternary Ag-In-Zn-S system,optimizes the Zn²⁺injection process,and finally using it as a light-emitting layer in electroluminescent devices.Further,the narrow band luminescence properties of Ag-in-S based semiconductor nanocrystals were regulated,and their growth process and luminescence mechanism were investigated.The specific work is as followed:（1）Firstly,the composition of the quaternary AIZS@Zn S nanocrystals was regulated to expand the luminescence range to the cyan region,which are synthesized by thermal injection.In order to further improve the luminescence properties of nanocrystals,different Zn²⁺injection processes were designed to optimize the epitaxial growth of Zn S.Green light nanocrystals with a photoluminescence quantum yield of up to 45.2%were obtained by dropping method.The analysis of the growth process of AIZS@Zn S nanocrystals demonstrate that the luminescence properties of AIZS@Zn S nanocrystals are mainly related to cationic reactivity.Finally,AIZS@Zn S nanocrystals synthesized by different Zn²⁺injection processes were used as the light-emitting layer to construct the electroluminescent diodes.（2）In order to obtain narrow band Ag-In-S-based semiconductor nanocrystals with high color purity,AIS@Ga S_x semiconductor nanocrystals were synthesized by seed growth nucleation with Ga³⁺coating.Narrow band AIS@Ga S_x semiconductor nano-crystalline was obtained by the composition control of Ag-in-S nanocrystals nucleation processes and coating processes,respectively,and the stable narrow band AIS@Ga S_xsemiconductor nanocrystals was obtained by the ligand and sulfur source regulation.By introducing ligands and adjusting the sulfur source and temperature of the nucleation reaction,the spectrum control range of narrow band was increased to 542-580 nm.Finally,the growth process,element distribution,crystal structure,and luminescence mechanism of AIS@Ga S_x semiconductor nanocrystals were explored.The narrow band luminescence of AIS@Ga S_x is attributed to the formation of tetragonal Ag Ga S₂.