Investigation On The Synthesis And Properties Of High-efficiency Luminescent Nanocrystals And Polyurethane Composites

Inorganic semiconductor nanocrystals(NCs)have potential application in the fields of solar cells and light-emitting displays because of their unique characteristics such as low cost,high carrier mobility,and large light absorption coefficient,etc.In recent years,it has attracted a lot of interests of scientific researchers.Cd Te NCs prepared by the aqueous phase method are simple to synthesize,and the solvent water used is environmentally friendly.The obtained NCs can be applied to bioimaging without ligand exchange,and therefore it has attracted people's attention.However,its stability is always the first problem to be solved in realizing its application.Especially,perovskite NCs developed in recent two years have the advantages of high photoluminescence efficiency,long carrier migration distance,easy to adjust emission color,and the performance in the field of optoelectronics is even more remarkable.However,currently reported perovskite NCs mostly require the use of a high boiling point solvent octadecene and stabilizers such as oleylamine and oleic acid.As known,the high boiling point solvent is not easily removed during the later device preparation process,affecting the efficiency of the device.At the same time,due to the presence of stabilizers with the long alkyl chain,it will also affect the carrier transport.In addition,perovskite NCs are susceptible to oxygen,ultraviolet,temperature and other effects,poor stability,difficult to regulate the morphology,limiting their application.One of the effective methods to address these issues is to incorporate these NCs into a polymer matrix that can retain the original properties of NCs and solve the problem of poor stability.The rational choice of the polymer matrix is crucial.Polyurethanes have the advantages of flexibility,strong carboxyl strength,and have excellent fatigue resistance,wear resistance,heat resistance,chemical resistance,and etc.It is commonly used in the field of security,coatings,adhesives,and automotive interiors,etc.Therefore,this thesis selects polyurethane as the matrix and successfully prepares composites of Cd Te NCs/polyurethane and perovskite NCs/polyurethane.The research carried out includes the following two parts:(1)Preparation of water-soluble Cd Te NCs and polyurethane composite materials.We first prepared Cd Te NCs in aqueous,then prepared the precursor of polyurethane prepolymer,and finally,the Cd Te NCs solution was added to the polyurethane precursor under stirring to emulsify to obtain an aqueous polyurethane dispersion.After evaporation and vacuum drying,a wavelength-tunable fluorescent anti-counterfeit composite material was obtained.The prepared fluorescent anti-counterfeit composite material was an invisible anti-counterfeit material.The composite would emission different colors under visible light and ultraviolet light,respectively,thereby playing an anti-counterfeiting effect.The obtained composites can be applied to the field of fluorescent anti-counterfeiting.(2)Preparation of high-efficient and stable luminescent perovskite NCs and its composite with polyurethane.We designed and synthesized polymerizable surfactant-modified hybrid perovskite NCs.The advantages of this system are simple synthesis steps,low cost,no use of high boiling point solvents and stabilizers,controllable morphology,polymerization,and low toxicity.The resulting NCs had a very highfluorescence quantum yield,up to 84%.By varying the length of the alkyl chain in the polymerizable surfactant,the fluorescence properties of the perovskite NCs were systematically regulated.By changing the amount of polymerizable surfactant in the surface ligand,its fluorescence emission was adjusted from 470 to 540 nm.The fluorescence lifetime of the obtained polymerizable NCs was about 20 ns.The perovskite NCs were successfully incorporated into polyurethane to form the composite of perovskite NCs and polyurethane.The composite materials retained the excellent photophysical properties of perovskite NCs,and had potentially application in coatings,anti-counterfeiting and other fields.