Design,preparation And Application Of Novel Low Toxicity Perovskite Quantum Dots

At present,with the vigorous development of China's economy,China's science and technology has also been developing rapidly.Since 1900,people all over the world have paid more and more attention to nanotechnology.At the same time,in this context,researchers have found a new kind of nano material all-inorganic perovskite quantum dot material,which is the most concerned one lead based perovskite quantum dots.In recent years,due to the advantages of inorganic perovskite quantum dots(QDs),such as high photoluminescence,high quantum yield(PLQYs,up to 90%),wavelength tunable,narrow half peak width,high carrier mobility,structural tunability and relatively low preparation cost,many researchers have paid attention to them.At the same time,due to these characteristics,perovskite quantum dots in solar energy batteries,photodetectors,light-emitting diodes(LED)and lasers can be widely used.However,in the environment of ultraviolet radiation,high temperature and hydration,perovskite quantum dots are relatively unstable.In addition,the characteristics of lead element toxicity limit the rapid development of industrialization in the field of optoelectronics.The main content of this paper is the preparation of all inorganic perovskite quantum material by heat injection method,the preparation of new perovskite quantum dot material with low toxic content by substituting gadolinium and gallium for the site of lead element in the structure,and the study of the influencing factors of fluorescence quantum yield of perovskite quantum dot material by substituting cesium ionon in the structure with lithium ionThe research content of this paper mainly includes the following aspects:(1)The fluorescence spectra of different rare earth ions Gd³⁺doped with Cs Pb Cl₃were studied.With the increase of Gd³⁺and Pb²⁺feed molar ratio,quantum dot luminescence occurred from blue to green under 365nm UV illumination.The transformation,followed by the PPMS system,found that it is paramagnetic with normal temperature,and the magnetic study of the doped Gd³⁺perovskite quantum dots shows the magnetocaloric effect(at?H=7.0 T and T=2.5 K,-?S_M^max=2.53 J kg^-1K^-1.These results indicate that perovskite quantum dots can be considered as potential refrigerants for low temperature applications.(2)The fluorescence spectra of different Ga³⁺doped Cs Pb Br₃were studied.With the increase of the molar ratio of Ga³⁺and Pb²⁺,the spectrum will undergo a red-shift under365nm UV illumination.When the feed molar ratio of the material of Ga³⁺and Pb²⁺is 1:1,PLQY reaches the highest,which is about 47%of blue light.And we successfully loaded the Ga³⁺doped perovskite quantum dots onto the cobalt borate crystal material.Through the protection of the vanadium borate crystals on the quantum dots,we found that the fluorescence intensity has no obvious quenching phenomenon for a long time.This greatly enhances the stability of the perovskite quantum.(3)We have successfully synthesized the Li⁺doped Cs Pb Br₃perovskite quantum dots by the improved thermal injection method.We find that the fluorescence spectrum of the quantum dots will undergo blue-shift compared with the undoped perovskite quantum dots with the different concentrations of the doped Li⁺.In this paper,we choose the lithium ion with smaller relative ion radius to replace the cesium ion in the structure.We find that the bond angle between lead and bromine become smaller.As a result,the octahedral torsion angle in the structure becomes larger,and the overlap density between the electron cloud and the electron cloud in the anti-bonding orbit between lead and halogen elements decreases.However,the band gap of the perovskite QDs is widened due to the weakening of the anti bond interaction between the two elements,resulting in a blue shift in the emission peak.It is also found that the fluorescence quantum yield increases first and then decreases with the increase of doping concentration.When the ratio of Li⁺to Cs⁺is 1.15,the fluorescence quantum yield reaches the highest,which is 47.99%.