Study On Preparation,Structure And Luminescence Characteristics Of Lead-free Halide Double Perovskite

All inorganic lead-free double perovskite makes up for the defects of toxicity and instability of lead based perovskite.With the development of double perovskite,exploring new halide double perovskite is helpful to expand the research in this field.Therefore,the research direction of this paper is the preparation of all inorganic halide double perovskite Cs₂B’B"Cl₆（B’=K and Ag,B"=Bi,In and Sb）,and to explore its crystal structure and luminescence characteristics.The specific content is as follows:（1）A new kind of halide double perovskite Cs₂KBiCl₆ material was successfully prepared by solid-state and liquid-state methods.The crystal structure of the material was studied by X-ray powder diffraction and neutron diffraction.According to the solid-state NMR spectra of¹³³Cs,the crystal structure of the material was formed by the displacement of Cs,K,Bi and Cl positions from the ideal position,with partial space occupied compensation.Cs⁺ions have distinct local coordination,forming an atomically disordered cubic structure.Through the low-temperature variable temperature diffraction test,it is found that within the temperature range of 5～300 K,the rising and falling temperature rate will affect the change of the material cell volume.When the sample is heated rapidly(the rate is 1 K·min^-1),the cell volume has a obvious hysteresis phenomenon.The direct band gap of Cs₂KBiCl₆ is estimated to be 3.35 e V by ultraviolet visible absorption.（2）Cs₂KBiCl₆ doped with different ions(Mn²⁺,Sb³⁺and In³⁺)was successfully synthesized by solid-state method,and its luminescence properties were studied.Excitation spectra showed strong absorption at 363 nm near ultraviolet light,and only very weak luminescence is observed in undoped compounds.Mn²⁺doped samples show strong orange-red luminescence（emission center at 600 nm）,and Sb³⁺doped samples show strong yellow-green luminescence（emission center at 525 nm）.Cs₂K_1-xBi_1-xMn_2xCl₆ has the highest luminous intensity at x=0.025,while Cs₂KBi_1-xSb_xCl₆ has the highest luminous intensity at x=0.15.In10%Sb:Cs₂KBi_1-xIn_xCl₆（x=0～1）samples,the emission center changes from 525 nm to 497nm and the emission intensity increases gradually.The photoluminescence changes from yellow-green to blue-green.（3）The halide double perovskite Cs₂KInCl₆ was successfully prepared by solid-state reaction method.The crystal structure of the halide double perovskite Cs₂KInCl₆ was studied by X-ray powder diffraction.It was found that its structure was similar to Cs₂KBiCl₆ with disordered cubic structure.The photoluminescence efficiency of Cs₂KIn_1-xSb_xCl₆ was improved by doping with Sb³⁺.The excitation spectra showed strong light absorption at 337nm and strong yellow-green luminescence at 495 nm in the sample doped with Sb³⁺.Compared with Cs₂KBi_1-xSb_xCl₆,blue shift appears in the emission center,and the emission intensity of Cs₂KIn_1-xSb_xCl₆sample is the highest at x=0.03.At the same time,the synthesis of Cs₂KSbCl₆ double perovskite has been explored by various means,but has not been successful and needs further exploration.（4）Three kinds of compounds Cs₂Ag B"Cl₆(B"=Bi³⁺,In³⁺and Sb³⁺)were prepared in air by a new synthesis method.The XRD data of Cs₂Ag BiCl₆,Rietveld structure fitting and SEM data uniform distribution of elements confirm the synthesis of three kinds of Ag-based compounds in air.This method makes up for the low production of liquid-state method and the complex operation of vacuum solid-state method,and also greatly improves the reaction cycle and sample purity.