Preparation And Optical Properties Of Blue CsBr Low Dimensional Nano Materials

Luminescent materials are an important part of life today,with a wide range of applications,from energy to information,environment and medical technology.Over time,various types of luminescent materials have been developed,including organic,polymer emitters,transition metal complexes,rare earth doped phosphor,nanocrystals and organic-inorganic hybrid perovskites.Among them,organic-inorganic perovskite materials and devices are the hot research field recently,and the light emitting diodes based on Ⅱ-Ⅵ family and metal halide perovskite semiconductor quantum dots（QDs）are considered as one of the most promising light sources for display applications due to their advantages of color tunable,high brightness,narrow emission bandwidth,solution processing capability and compatibility with flexible substrates.However,it contains toxic heavy metal element lead,which not only causes harm to human body,but also pollute the environment to varying degrees.Therefore,people hope to prepare environmentally friendly,efficient and stable materials and devices.So far,the efficiency and stability of red and green quantum dot light-emitting diodes（QLEDs）have been significantly improved by optimizing low-dimensional light-emitting materials and device structures.However,as one of the three primary colors,blue QLEDs lag behind red and green QLEDs in terms of device efficiency and stability.Therefore,the preparation of high quality non-toxic or low toxic blue nanomaterials is the key to achieve panchromatic display of luminescent materials in the future.In this paper,Csand Br ions were used to synthesize CsBr nanomaterials with high luminescence efficiency under the action of ligands.By studying the optical properties of materials under different reaction conditions,a method of synthesizing efficient and stable luminescent materials was found;To further understand its luminescence mechanism,CsBr nanomaterial was modified with SiO₂ to improve its luminescence efficiency and stability,and a preliminary attempt was made to prepare LED devices.The specific contents are as follows:（1）Preparation and properties of CsBr quantum dots.The CsBr quantum dots emitting blue light were prepared by ligand-assisted reprecipitation method at high temperature（e.g.150℃）.The crystallinity and optical properties of the nanomaterial were investigated.According to the characterization results,the CsBr quantum dots have high crystallinity and are quasi-spherical with uniform morphology and size,and the crystal size is 19 nm.There are three absorption peaks at 353 nm,373 nm and 394 nm,and three fluorescence emission peaks at 403 nm,428 nm and 453 nm,respectively,with a large Stokes shift.The fluorescence quantum efficiency is up to 92.05%.It is found that CsBr QDs have negative thermal quenching behavior with activation energies of 5.58 meV and 11.57 meV by temperature changing fluorescence analysis,and the luminescence mechanism of CsBr QDs is mainly caused by defects or surface states combined with time-resolved spectroscopy and transient absorption.（2）Stability of CsBr quantum dots and application of white LED.It is found that CsBr quantum dots have better irradiation resistance and better optical stability when irradiated by UV lamp for different time.In the study of thermal fatigue performance of CsBr quantum dots,the fluorescence intensity of CsBr quantum dots can still be restored after more than four heating and cooling cycles with the temperature range from 0℃to 80℃controlled by water circulation system.After that,we mixed CsBr quantum dots with Y₃Al₅O₁₂（YAG）phosphors to make lead-free white diode（WLED）devices based on the high efficiency of CsBr quantum dots in oil phase.（3）Preparation and properties of CsBr nanorods.Blue emitting CsBr Nanorods（NRs）were prepared by ligand-assisted reprecipitation at room temperature（e.g.45℃）.Firstly,the preparation process was optimized,and finally CsBr nanorods with quantum efficiency up to 48.95%were prepared.CsBr nanorods have good crystallinity and uniform dispersion.Subsequently,CsBr nanorods were modified with different amounts of SiO₂ to effectively improve their luminescence intensity and stability.