Synthesis And Luminescence Properties Of Copper-doped Cadmium-based Chalcogenides Nanomaterials

In the past few decades,the introduction of transition metal ions into semiconductor nanocrystals(NCs)has attracted significant attention among researchers.The introduction of doped ions can form new recombination centers,so that the semiconductor NCs exhibit optical properties related to doped ions.These unique properties endow doped semiconductor NCs for application in light-emitting diodes,biological labeling as well as photocatalysis.Among the family of transition metal ions,manganese and copper ions are the two most common doped ions.In recent years,material synthesis,structural control and optical properties of Mn-doped semiconductor NCs,as well as optoelectronic and biomedical applications,have received extensive attention and achieved rapid development.As compared to Mn-doped semiconductor NCs,less attention was paid to the study of Cu-doped NCs,especially to the research on the synthesis of Cu-doped semiconductor NCs and the regulation of optical properties.Due to Cu ions have the large mobility at high temperature,and they diffuse inside the NCs easily,thereby making it difficult to control the doping position of Cu ions.Therefore,it is necessary and challenging to control the doping position of Cu ions in NCs,especially in core-shell NCs and study the dopant position dependent optical properties.Hence,this paper focuses on the synthesis and optical properties regulation of cadmium-based semiconductor NCs with different Cu-doped nanostructures and the effect of Cu-doped position on its optical properties,so as to explore its formation mechanism and luminescence mechanism.On the basis of doped NCs,the performance of quantum dot light-emitting diode(QLED)devices based on Cu(I)-doped alloy Cd Zn S NCs was preliminarily studied.The specific research work is as follows:(1)CdS and CdS:Cu NCs were synthesized with n-dodecanethiol(DDT)as sulfur source by one-step method.The introduction of Cu(I)makes the photoluminance(PL)of CdS nanocrystals mainly changed from defect-state emission to Cu(I)-related donor-acceptor(D-A)pair composite emission.The growth of Zn S shell on the surface of CdS NCs effectively reduces the defect-state emission,and the exciton emission peak at 435 nm has obtained.Then,the Zn S shell was grown on the surface of CdS:Cu(I)NCs by in-situ method and seed-growth method by controlling the injection of precursor solutions.The emission peak was somewhat red-shifted,but the exticon peak of CdS NCs was not observed.To realize the successful doping of Cu(I)ions into CdS/Zn S core/shell NCs,making CdS/Zn S NCs as seeds,different amounts of Cu ions were introduced into NCs.The PL intensity of the exciton emission peak at 436 nm is decreased but the Cu(I)-related emission peak at 680 nm together with an enhanced and dominant PL emission.The emission is consistent with the PL of the CdS:Cu(I)NCs without the Zn S shell,indicating that the Zn S shell was successfully grown on the surface of the CdS:Cu(I)NCs.In order to explore its growth mechanism,by heating CdS:Cu(I)/Zn S NCs in an inert solvent,it was found that the intensity of the exciton emission peak gradually weakened,while the Cu(I)-related emission peak increased,indicating that the introduction of Cu(I)ions is mainly based on the diffusion of Cu ions.Finally,the introduction of Cu(I)ions into the Cd Zn S alloy NCs was achieved.Then,the Cu(I)-doped NCs with the red light were applied to QLEDs,and the Cu(I)-related electroluminescence(EL)was obtained.(2)In order to further verify the doping of Cu(I)ions in CdSe NCs,cubic phase CdSe NCs were prepared by one-step method.By changing the experimental conditions,the PL of CdSe NCs in large visible light range was achieved.On the basis of CdSe NCs,Cu ions were successfully introduced into the CdSe NCs,the intensity of the exciton emission peak gradually weakened,and the Cu-relate emission peak in the red light range was enhanced,and the PL lifetime increased from 23 ns to 327 ns.Afterwards,the CdSe:Cu NCs were coated with a low-temperature single precursor solution.The results showed that the coating of the Zn S shell layer increased the exciton emission intensity,thereby reduce the Cu-related emission.This PL properties are different from the Zn S coating on CdS:Cu(I)NCs surface,indicating that the diffusion of copper ions in different chalcogenide NCs is different.