Controllable Synthesis And Properties Of CsPbX3(X=Cl,Br,I) All-inorganic Perovskite Quantum Dots

All-inorganic halide perovskite quantum dots?QDs?have been considered to be the most promising new optoelectronic materials at present,owing to their excellent photoluminescent properties,such as easily adjustable band gap,narrow emission spectrum,wide spectral absorption and high quantum efficiency,and have broad application prospects in solar cells,LED,lasers,biological imaging and other fields.At present,the most commonly used method to synthesize all-inorganic perovskite quantum dots is the high temperature hot-injection technology,but the method has the shortcomings of complex operation,high cost and long time consuming.Meanwhile,the halide perovskite quantum dots all contain the heavy metal element Pb,which will cause some pollution to the use environment,which is not in accordance with the concept of environmental protection in the world today.Moreover,the perovskite quantum dots materials are extremely sensitive to environmental factors such as the air and water,owing to the essential properties of ionic crystals,which can greatly reduce their stability.It will also become an urgent problem to be solved in the future industrial application process.Therefore,novel all-inorganic halogen perovskite quantum dots with relatively low cost,low toxicity and high stability need to be developed.In response to the above problems,a series of novel all-inorganic halogen perovskite quantum dots have been developed to reduce the preparation cost,reduce toxicity and improve stability in this paper.On this basis,the synthesis conditions,particle morphology,crystal structure and optical properties of these perovskite quantum dots are systematically analyzed.The work summarized as follows.?1?The traditional hot-injection technology is improved to simplify the operation flow,reduce the cost of synthesis and shorten the reaction time.The cubic phase CsPbBr3perovskite quantum dots with excellent optical properties were prepared by using improved hot-injection technology to verify the feasibility of the improved method.On this basis,the panchromatic emission from 412 nm to 700 nm is successfully obtained by regulating the species and content of halogen ions.The color purity is over 96%and the color gamut covering up to 139%of the NTSC color standard.After that,the effective control of the perovskite quantum dot size is realized though controlling the reaction temperature,and then the precise control of the emission wavelength is obtained in a small wavelength range?514-523nm?.However,the change of reaction temperature has no obvious effect on the full width at half-maximumx,lifetime,color coordinate and color temperature of perovskite quantum dots.?2?The metal cation doping of CsPbCl3 perovskite quantum dots is performed.The Cs(Pb_xMn_1-x)Cl₃,Cs(Pb_1-xBi_x)Cl₃,Cs(Pb_1-xEu_x)Cl₃?Cs(Pb_0.95-x.95-x Bi_0.05Eu_x)Cl₃ are successfully obtained by using the improved hot-injection technology on the basis of guaranteeing the optical properties of quantum dots.The dual emission of excitons and doped ions(Mn²⁺,Bi³⁺,Eu³⁺)is obtained in perovskite quantum dots,and then realize the effective control of its luminous color.Among them,the exciton emission peak sites of the four perovskite quantum dots all show blue shift with increasing doping concentration,but the emission peak sites of the doped ions all show red shift,and their intensity increases with increasing doping concentration.The variation of doping ion content has no obvious effect on the morphology and crystal structure of the four perovskite quantum dots,but the particle size decreases with the increase of doping concentration,and the characteristic diffraction peak sites drift to a high angle with the increase of doping concentration.The fluorescence lifetime of quantum dots host decreases with increasing doping concentration,owing to the CsPbCl₃ host?Mn²⁺,CsPbCl₃ host?Bi³⁺,CsPbCl₃ host?Eu³⁺and CsPbCl₃ host?Bi³⁺?Eu³⁺energy transfer process.Subsequently,the characteristics of low temperature luminescence of Cs?PbxMn1-x?Cl3 are investigated in the 10-298 K temperature range,and their activation energy of?26.7 meV,indicating that it has good thermal stability.?3?The surface of CsPbX3 and Cs?Pb,Mn?Cl3 perovskite quantum dots is modified to develop a novel method for silica coating quantum dots at room temperature.Using the perovskite quantum dots as precursor and the high hydrolysis rate methyl orthosilicate as silicon source,the hydrolysis of tetramethoxysilane was further promoted by adding extra trace deionized water to obtain spherical CsPbX₃@Si O₂ and Cs?Pb,Mn?Cl₃@Si O₂ quantum dots.Taking CsPbBr3 quantum dots as an example,the optimal amount of deionized water is determined to be 0.35 vol%.The growth mechanism of CsPbBr3@Si O2 is briefly introduced and a simple quantum dots structure model is constructed.The stability of samples ia then tested.The intensity of the emission peak intensity of CsPbBr3@SiO2 quantum dots dispersed in a mixed solution of toluene and water retained 77%of the initial value even after 12 h,much higher than that of pure CsPbBr₃ quantum dots.Applying this method to the preparation of other halogen CsPbX3@SiO2 quantum dots,the stability test shows that the air and water stability of the coated quantum dots are obviously improved.In addition,the Cs?Pb,Mn?Cl3@SiO2 quantum dots were synthesized.The main emission peak intensity of quantum dots after coating could effectively retain 64%of the initial value though the water stability test,,while the pure quantum dots only maintained 31%.The silica layer can effectively block the contact between perovskite quantum dots and the external environment?air,water,ethanol,etc.?,thus,avoiding the destruction of the luminescence properties of quantum dots by external unfavorable factors.