High Photostability Of Quantum Dots:Epitaxial Al₂O₃ Self-passivation Layer With A Homogeneous Ligand

Semiconductor quantum dots?QDs?exhibit excellent luminescent efficiency,color-adjustable spectra,and narrow emission width.These properties are extensively used in applications,including LED,solar detectors,and biotags.However,the photo-instability and degradation of QDs are observed to remain considerable challenges.Because of their high specific surface areas,colloidal QDs are susceptible to various environmental influences The stability of quantum dots will be a great challenge in practical applications,so it is necessary to find an effective method to solve this problem.In this paper,CdSe/CdS,CdSe/nCdS/Al QDs and CsPbBr₃,CsPbBr₃/nZnS/Al QDs were successfully prepared by traditional thermal injection and Al layer coated with the same ligand.Meanwhile,the molar ratio of potassium to oleate?K-oleate?was controlled.Monodisperse K-CsPbBr₃ QDs were synthesized and the self-passivation layer of alumina?Al₂O₃?was grown by the same method.Meanwhile,the radiation behavior,non-radiative relaxation processes,and exciton–phonon interactions of QDs can be understood by measuring their temperature-dependent PL spectra.The main contents are as follows:The CdSe/CdS and CdSe/2CdS QDs were successfully prepared by TC-SILAR method and the Al layer was coated by the same ligand.The optical stability of QDs was improved and the fluorescence intensity of QDs was maintained.Compared with the QDs without Al layer,the optical stability of CdSe/CdS/Al and CdSe/2CdS/Al is greatly improved.Under the irradiation of strong LED,the fluorescence can still be maintained well.According to the test results in this paper,the optical stability of CdSe/CdS/Al and CdSe/2CdS/Al is much higher than that of QDs without coated Al layer.We speculate that this is mainly due to the action of Al-self-passivation layer,increasing the temperature of the sample in the process of light irradiation to cause the oxidation reaction,protecting the QDs from photodegradation and water-oxygen erosion.The CsPbBr₃ and CsPbBr₃/ZnS QDs were synthesized by high temperature hot injection method,CsPbBr₃/ZnS/Al and CsPbBr₃/2ZnS/Al QDs were successfully prepared by coating Al layer with the same ligand.The luminescence intensity,peak energy and FWHM of CsPbBr₃,CsPbBr₃/ZnS,CsPbBr₃/ZnS/Al and CsPbBr₃/2ZnS/Al QDs were studied.The results show that the luminescence of CsPbBr₃ QDs mainly comes from exciton recombination.The emission spectra are blue-shifted due to the interaction of electron-phonon coupling and thermal expansion.The decay process of PL fluorescence lifetime of QDs films is further discussed.LED blue light self-passivation is used to produce Al₂O₃ to prevent the degradation of QDs.The optical stability tests show that the stability of CsPbBr₃/ZnS/Al and CsPbBr₃/2ZnS/Al QDs is improved obviously.By controlling the molar ratio of potassium to cesium in K-CsPbBr₃ solution,monodisperse potassium modified K-CsPbBr₃ QDs,was successfully synthesized by using the same ligand-coated Al layer to prepared K-CsPbBr₃/Al QDs.Under the continuous irradiation of LED,it was found that the optical stability was significantly enhanced.The optical stability test showed that after 3 hours of irradiation,the PL intensity of CsPbBr₃ solution decreased to half of that of the original solution,while the PL strength of K-CsPbBr₃/Al solution decreased only 15%after 18 hours of irradiation.By testing the morphology,structure and composition of K-CsPbBr₃ and K-CsPbBr₃/Al QDs,the results can be attributed to the modification of K⁺,which may result in the formation of a strong potassium-related passivation layer on the surface of K-CsPbBr₃ QDs.At the same time,the effect of surface defects on the luminescence of QDs is greatly reduced.