Preparation And Spectral Control Of Copper And Manganese Co-Doped Cesium Bromide Nanocrystals

CsBr crystal has the characteristics of wide band gap and easy to combine with metal ions,which is a potential doping host for high-quality luminescent materials.Most of the ion-doped CsBr reported so far are bulk crystals,which have low fluorescence quantum efficiency and require high temperature conditions and a tedious cooling process.Reducing the grain size of CsBr crystals to nanoscale can enhance radiative recombination and reduce surface defects,leading to higher fluorescence quantum efficiency.However,most of the reported ion-doped CsBr nanocrystals cannot achieve continuous regulation of fluorescence emission.In order to expand the color gamut of doped CsBr nanocrystals,the emission wavelength of the nanocrystals can be tuned by adjusting the halogen composition.However,nanocrystals based on mixed halogen compositions exhibit poor color stability due to the migration of halogen ions under field driving.Therefore,it is necessary to develop a new strategy to prepare CsBr nanocrystals with tunable emission wavelength and high color stability.In this work,a cationic double doping strategy is proposed to control the color gamut of CsBr nanocrystals.The research mainly focuses on the preparation and fluorescence regulation of copper-and manganese-doped CsBr nanocrystals.The specific contents include:Firstly,the properties of Cu-doped CsBr(Cu:CsBr)nanocrystals prepared by the reported ultrasonic method and the newly proposed heating method were investigated,and it was confirmed that the nanocrystals prepared by the heating method had higher fluorescence quantum efficiency.The characterization by X-ray diffraction and X-ray photoelectron spectroscopy confirmed that all Cu:CsBr nanocrystals were prepared by ultrasonic method and heating method.The results of transmission electron microscopy showed that the average sizes of Cu:CsBr nanocrystals prepared by the two methods were different.In this thesis,the optimal conditions for the preparation of Cu:CsBr nanocrystals by the heating method are determined as follows: the reaction temperature is 130℃,the reaction time is 10 min,and the Cu:Cs feeding ratio is 1:2.Under the optimal experimental conditions,Cu:CsBr nanocrystals exhibited blue emission with a fluorescence quantum efficiency of 38.8%,which was higher than the previously reported fluorescence quantum efficiency of Cu:CsBr nanocrystals prepared by ultrasonic method.In this thesis,the effect of Mn ions introduced into the Cu:CsBr nanocrystal system on the luminescence of nanocrystals has been preliminarily explored.The experimental results show that the addition of Mn ions enhances the fluorescence intensity of Cu:CsBr nanocrystals when using the ultrasonic method;while using the heating method,the addition of Mn ions makes the nanocrystals have double peak emission at 456 nm and 538 nm.Secondly,the luminescence properties of bimodal emission Cu and Mn co-doped CsBr(Cu,Mn:CsBr)nanocrystals prepared by heating method were further studied.Through Xray diffraction,X-ray photoelectron spectroscopy and transmission electron microscopy,it was proved that both Cu ions and Mn ions entered the CsBr nanocrystals in the form of doping.In this thesis,the reaction conditions of Cu,Mn:CsBr nanocrystals are optimized.When the reaction temperature is 150℃,the reaction time is 30 min,and the Cu:Cs feeding ratio is 1:2,the fluorescence intensity of the nanocrystals is the strongest.By adjusting the feeding ratio of Mn ions and Cu ions,the relative intensities of the two emission peaks at 456 and 538 nm can be flexibly controlled,so that the fluorescence color can be transferred from the blue region to the green region.In this thesis,the role of HBr in the doping of Mn ions is studied.The results show that HBr significantly promotes the doping of Mn ions into CsBr nanocrystals,and the introduction of HBr also helps alleviate the effects of high Mn doping.The phenomenon of MnMn interaction and double exciton recombination can be realized,so as to realize the efficient Mn-doped fluorescence emission.At last,the luminescence mechanism of Cu,Mn:CsBr nanocrystals is investigated.The existence of the energy transfer channel from the Cu level to the Mn level is proved by the test of the fluorescence lifetime of the Cu level exciton transition,which leads to the decrease of the fluorescence lifetime of the Cu level exciton transition after Mn ion doping.To demonstrate the potential application of the prepared nanocrystals,a multicolor fluorescence-converted LED was fabricated using Cu,Mn:CsBr nanocrystal@polystyrene composite film as the color conversion layer.