Controllable Synthesis Of ?-? Group Semiconductor Quantum Dots And Their LED Applications

Recently,quantum dots(QDs),especially II-VI group QDs,have been extensively researched because of their outstanding optical properties,for instance,the bandgap adjusted by the size and constituent of the QDs,narrow full-width at half-maximum(fwhm),and excellent optical and thermal stability.So far,the synthetic method of ?-? group QDs could be grossly divided into two categories based on the reaction system:oil phase method and aqueous phase method.For oil phase method,the obtained QDs generally have highly crystallinity and good monodispersity due to the high reaction temperature,however,the long-chain and hydrophobic ligands on the QDs' surface prevent the application in the biological field,and the carriers transporting between the adjacent QDs in the optoelectronic devices.Compared with the oil phased method,the low synthetic temperature(?100?)could lead to the lower crystallinity and worse monodispersity in the aqueous phase method.And the crystallinity and dispersity of the QDs are important to the optical and electronical properties.The reagents contained phosphine were widely used in the oil phased method,however,these reagents are generally expensive and harmful to the environment.And the obtained uncoated QDs have low quantum yield(QY)and are easily be influenced by the ambient.Thus,it is essential to develop a non-phosphine method to synthesize QDs,and implement the coating reaction to improve the QDs' QY and the optical and thermal stability,and then the obtained core-shell QDs could be used to fabricate WLED with excellent properties.Furthermore,the original long-chain ligand could be exchanged to short-chain ligand or inorganic ligand,and thus improving the transport performance of carriers.Consideration form the above-mentioned factors,this dissertation started with the different precursors and solvents to synthesize CdSe,CdTe,CdSexS1-x,CdZnTe QDs.And the coating shell reactions were executed to improve the QY and the optical and thermal stability,the original long-chain ligand was also instead by inorganic ligand and short-chain ligand.The main results are as follows::1.The CdSe QDs were synthesized by hot injection method and aliphatic amine ligands.The nucleation and growth process influenced by the different injection temperature,growth time and aliphatic amine ligands was studied by the absorption and emission spectra,XRD and TEM measurement.The results demonstrated that the monodisperse and pure zinc-blende CdSe QDs with the size of 3.5 nm could be obtained by using oleylamine as ligands and at 250? and 12 min.In the CdSe QDs synthetic process,the QDs' crystal structure would translate from zinc-blende to wurtzite by the aliphatic amine ligands.2.Based on the CdSe/CdS core-shell QDs as the subject investigated,an two-type(X-type and Z-type)ligand-exchange reaction was presented.Compared to the one-type ligand-exchange reaction,the CdSe/CdS QDs could be transferred from the non-polar solvent to polar solvent more efficiently,and the QDs' morphology and size were not change in two-type ligand-exchange reaction.What's more,the most of QY and the stability of QDs could be persisted.3.A varity of core QDs(CdSe and CdTe)and core-shell QDs(CdSe/CdS,CdTe/CdS,CdTe/CdSe and CdSexS1-x/CdS)were synthesized by non-phosphine method and in different solvents and systems,and then the core-shell QDs were used to fabricated WLED.Firstly,using the SeO2 as the Se precursor and in the octadecylene solvent,a series of CdSe QDs with different size(2.4-5.7 nm),monodisperse,zinc-blende structure and the emission of 550-635 nm covered the area of green to red,could be obtained by optimizing the synthetic conditions.Then the CdSe/CdS core-shell QDs with QY high up to 65%could be synthesized by a mono-precursor coating shell reaction.A WLED with outstanding optical properties,a color rendering index of 92.9,a color temperature of 4400 K,a color coordinate of(0.3583,0.3349)and a luminous efficiency of 63.54 lm·W-1,obtained by using these core shell QDs.Furthermore,CdTe QDs were synthesized via one-pot method in octadecylene and liquid paraffin,and the corresponding CdTe/CdS and CdTe/CdSe ?-type QDs with a QY high up to 75%were synthesized by employing a non-phosphine and in-situ coating method.These production is benefit for the large-scale synthesis of QDs and promotes the application of QDs.4.In aqueous solution and use Mercapto propionic acid as the ligand,the CdZnTe QDs were synthesized via hot-injection method.And the CdZnTe/Na2CO3 compound were obtained by coprecipitation,which were used to fabricated WLED successfully.Highly crystalline CdZnTe QDs with zinc-blende structure and the emission of 550-610 nm were synthesized by adjusting the reaction time.And the QY of CdZnTe QDs could up to 41%.Adding a quantitative Na2CO3 to the QDs solution,the CdZnTe/Na2CO3 compound was obtained by adding excessive ethanol.The compound have a QY of 21%and good fluorescence stability.And the WLED with excellent optical properties,a high color rendering index of 92.7,a color temperature of 4146 K,and a color coordinate of(0.3662,0.3396),were fabricated by these compounds.