| Semiconductor nanocrystals with quantum confinement regions,also known as quantum dots?QDs?,have unique optical and electrical properties such as continuously tunable emission wavelengths,broad excitation spectra,narrow emission spectra,high fluorescence quantum yield and photochemical stability and anti-fluorescence bleaching due to their quantum size effects.So semiconductor nanocrystals are widely used in light emitting diodes?LED?,bioassays,lasers,and solar cell sensitizers and have a great development in recent years.At present,high quality fluorescent quantum dots are often prepared by colloidal chemistry?such as metal organic synthesis?.In the process of synthesis,on the one hand,the growth of high band gap on its low band nucleus makes the surface of the quantum dots passivated.On the other hand,the organic ligands are introduced on the surface of the quantum dots,which make the quantum dots uniform and soluble in a variety of organic solvents,and the photoluminescence quantum yield?PL QY?is relatively stable.However,when QDs are applied to optical devices such as LEDs,they often need to be mixed with silicon resin.The separation of QDs from the original solvent may cause the removal of the solvent on the surface,which may lead to more surface defects and the aggregation of the quantum dots.In addition,the heat curing process will also cause the fluorescence quenching of the quantum dots.Therefore,how to stabilize quantum dots in matrix is the key problem for their practical application in solid-state devices.In order to expand the application of QDs in solid state display and lighting,it is a feasible method to encapsulate quantum dots into thin films.At present,researchers have developed various methods for preparing quantum dots photoluminescent thin films,such as spin coating,trickle down,and crystal coprecipitation.But they usually exist such problems as phase separation,quantum dot aggregation or fluorescence quantum yield reduction.Therefore,how to fabricate quantum dot luminescent film with ideal structure,high processing property and stability is still a task of great challenge.In this paper,we firstly synthesized high quality CdSe/ZnS QDs with core-shell structure by optimized organic phase synthesis method,and then made them water soluble through surface modification.Then the ordered and controlled quantum dot photoluminescence films were prepared by electrostatic spinning and layer-by-layer self-assembly.On this basis,we further explored the influence of the two preparation methods on the luminescent properties of quantum dots.It mainly included the following two aspects:?1?Study on preparation and properties of poly?ethylene oxide?quantum dots?PEO-QDs?nanofiber thin films based on electrospinning technology.First,the oil soluble core-shell CdSe/ZnS QDs were coated with amphiphilic oligomer?polymaleic acid n-hexadecanolester,PMAH?to obtain stable water soluble QDs.Then using polyethylene oxide?PEO?as the polymer template and water as the solvent,by optimizing the experimental parameters in the electrostatic spinning process,the monochrome and compound color PEO-QDs nanofiber thin films were prepared.On this basis,it was characterized by scanning electron microscope?SEM?,fluorescence microscopy,infrared spectrum?FTIR?,fluorescence spectrum and so on.The results showed that the surface of PEO-QDs composite fiber film was smooth and non adhesion,the average diameter was 215 nm.The fluorescence characteristics of QDs in PEO-QDs film have no obvious change before and after compound with PEO,and there was no obvious forster resonance energy transfer?FRET?phenomenon in the two-color film,which show feasibility of this method for preparing photoluminescence composite thin films of polymer quantum dots for illumination and display direction.?2?Study on preparation and properties of high stability SiO2/PEI-QDs photoluminescent thin films based on layer-by-layer assembly method.First,polyethyleneimine?PEI?was used to modify the oil soluble core-shell CdSe/ZnS QDs by ligand exchange method to obtain stable water-soluble PEI-QDs.Then,using sodium silicate as precursor of SiO2,multilayer red,green and blue SiO2/PEI-QDs thin films were obtained by layer-by-layer assembly with PEI-QDs.The results of fluorescence spectrum,atomic force microsco?AFM?and SEM show that the intensity and thickness of thin films can be precisely controlled by changing the number of assembly layers.After two hours of continuous ultraviolet radiation and 60°C at constant temperature,the fluorescence intensity of the films remain above 83%of the initial value,showing high photothermal stability,which is very important for its practical application.On this basis,by accurately controlling the ratio between three monochromatic thin films,the white light emitting film was obtained with the color coordinates at?0.3501,0.3401?,very close to the standard white light color coordinates,it's color rendering index?CRI?is 81 and the correlated color temperature?CCT?is reduced to 4676 K,which belongs to the high quality QDs photoluminescence thin film.The film has great potential in solid-state lighting,multicolor display and sensing. |
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