Investigation On Luminescence Mechanism And Preparation Of Lead Cesium Bromide Quantum Dot Glass Ceramics

In recent years,all inorganic lead cesium perovskite quantum dots have shown great application prospects in the fields of X-ray imaging and visible light communication because of their high luminous purity,short fluorescence lifetime,high photoluminescence quantum yields and low preparation cost.At present,the preparation methods of lead cesium bromide perovskite quantum dots are mainly divided into supersaturation crystallization method and heat injection method.However,the quantum dots prepared by these two methods are very prone to anion exchange reaction,and their thermal and chemical stability are poor,which greatly limits the application scenario of lead cesium bromide quantum dot materials.Not only that,the photoluminescence mechanism of lead cesium bromide quantum dots is still controversial in academic circles.The glass network with stable physical and chemical properties is taken as the carrier for this subject,the stability of quantum dots was improved by growing lead cesium bromide quantum dots in glass matrix,and the luminescence mechanism of lead cesium bromide perovskite quantum dot glasses synthesized by different preparation methods was deeply studied,the correlation between glass preparation method,luminescence mechanism and optical properties is proved,so as to continuously improve the fluorescence quantum yield of lead cesium bromide quantum dot glass materials.At the same time,light-emitting diode devices based on high-purity green light-emitting CsPbBr₃ quantum dot glass are constructed,and the application fields of perovskite quantum dot glass materials（thermal temperature measurement and scintillator）are widened.This research has important academic significance for promoting the application of lead cesium bromide quantum dot glass materials in the field of optoelectronic devices.The dissertation includes the following six chapters.The first chapter is literature review,the classification and development history of perovskite quantum dots are briefly summarized.Firstly,the synthesis methods and application fields of perovskite quantum dots are introduced.Secondly,the research status of perovskite quantum dot glass materials is introduced,including its synthesis methods,luminescence mechanism and optical properties,which leads to the content and research background of this paper.The second chapter is the relevant experimental methods and theoretical calculation basis.This part mainly introduces the preparation methods of lead bromide cesium perovskite quantum dot glass samples and the related performance test methods,as well as the corresponding experimental test instrument information.In addition,the relevant theoretical calculations are also calculated and displayed in this part,including the definition formulas and calculation methods of some specific physical parameters.The third chapter is the study on the preparation and luminescence mechanism of CsPbBr₃ quantum dot glass by friction crystallization method.A new type of non-rare earth doped dual emission（460nm and 512 nm）CsPbBr₃ quantum dot was obtained in tellurite glass by friction crystallization method,the internal energy was produced by frictional work,the heat from friction enables structural relaxation of the glass with a decreased viscosity,resulting in easy diffusion and rearrangement of atoms or structural units,and thus of nucleation and crystal growth in the surface of broken glass powder.In addition,the intrinsic luminescence of 512 nm from quantum dots and 460 nm from thermally induced bromine vacancies are proved by electron paramagnetic resonance spectroscopy and variable temperature fluorescence lifetime.The variation trend of the two fluorescence emission peaks with temperature shows that they have the potential to be used in fluorescence thermal temperature measurement.Combined with the simulation results of correlation fluorescence intensity ratio,fluorescence intensity ratio results indicate that the relative sensitivity of dual-emission could reach 5.6%K^-1 at 323 K,this discovery of non-RE doped CsPbBr₃ QDs glass-ceramic with negative thermal quenching uncovers a new optional sensing glass material that surpass traditional RE-doped QDs glass by their tunability and sensitivity.The fourth chapter is the study of the effect of Ag⁺doping on the luminescence properties of CsPbBr₃ quantum dot glass and its mechanism,the photoluminescence efficiency and color purity of CsPbBr₃ quantum dot glass directly prepared by heat treatment are low,which greatly limits its practical application.In this chapter,Ag⁺doped self-crystallizing CsPbBr₃ quantum dot glass was successfully prepared by melt quenching.Compared with the conventional heat-treated CsPbBr₃quantum dot glass,its photoluminescence efficiency was increased by 10 times.Among them,the reason for self-crystallization is that with the increase of Ag⁺doping concentration,when Cs,Pb and Br ions change from liquid to solid,the free energy of high-temperature melting system decreases and the crystallization driving force increases.Therefore,small-size CsPbBr₃ crystals can be formed during annealing.In addition,combined with transmission electron microscopy and X-ray photoelectron spectroscopy,it can be found that the improvement of photoluminescence efficiency of Ag⁺doped self-crystallization CsPbBr₃ quantum dot glass is related to the plasma resonance effect produced by Ag nanoparticles around CsPbBr₃.The green light-emitting devices based on bulk self-crystallization CsPbBr₃ QD glass with 0.4 mol.%Ag⁺doping achieves a luminescence efficiency of 20.85 lm/W with a CIE（0.2084,0.6026）under a 20 m A driving current.The fifth chapter is the preparation of low dimensional Cs₄Pb Br₆ quantum dot glass by molten salt method and its luminescence mechanism.Herein,Cs₄Pb Br₆quantum dots（QDs）glass ceramics,which can be used as scintillator materials,were fabricated by molten salt method.The perovskite glass ceramics not only maintained the original high air stability of glass,but also had high quantum yield（49.7%）and crystallinity.Not only that,QDs-based solid powder exhibited strong green luminescence under the illumination of both X-ray and UV light.In addition,a novel dual emission is observed in the radioluminescence spectra of Cs₄Pb Br₆ QDs.Electron paramagnetic resonance（EPR）and X-ray diffraction（XRD）suggested that the novel dual-emission is associated with the Br vacancy.It is worth noting that after repeated X-ray irradiation,the radioluminescence（RL）intensity of the Cs₄Pb Br₆QDs glass ceramic sample can be increased to 6.2 times of the initial intensity,which provides a new idea for the long-term repeated use of scintillator materials.These results demonstrated that the Cs₄Pb Br₆ QDs glass ceramics are promising materials in scintillator fields.The sixth chapter is the conclusion,which briefly summarizes and summarizes the work done in the full text,and points out the deficiencies in the work and the prospect of future work.