Synthesis And Optical Properties Of Lead Free Double Perovskite Cs₂AgInCl₆

The problem of lead poisoning in lead halide perovskite has caused serious harm to the ecological environment and human health,which has aroused widespread concern all over the world.Therefore,it is necessary to find efficient and stable lead-free perovskite substitutes.Lead-free double perovskite Cs₂AgInCl₆is considered to be a potential substitute material due to its good stability,long carrier life,easy processing and direct band gap.However,Cs₂AgInCl₆still has the following problems:limited by the parity forbidden transition,the luminous efficiency is not high enough;its excitation light source has to choose the ultraviolet light source or the light source with higher excitation energy,which is not conducive to the future application and development;the emission line is too wide,which is only suitable for the lighting field,and can not be applied in the field of display devices;The stability is not enough to reach the level of practical commercial application.In this paper,the structure of Cs₂AgInCl₆was adjusted by SiO₂to improve its luminescent intensity and stability;Cs₂K_xAg_0.6Na_0.4In_0.8Bi_0.2Cl₆Br_xand Cs₂K_xAg_0.6Na_0.4In_0.8Bi_0.2Cl₆I_xwere prepared,and the orange and red pure color light emission was realized.The details are as follows:In order to improve the emission intensity and stability of Cs₂AgInCl₆,SiO₂was used to adjust the structure of Cs₂AgInCl₆.The growth mode and crystal morphology of Cs₂AgInCl₆changed from octahedron to truncated octahedron through SiO₂.After the change of structure,the unit cell disperses and breaks the absorption limit.SiO₂passivates the surface of the material and forms an anti-oxidation protective film.Consequently,the photoluminescence emission intensity increased by 181.5%and the stability improved by 83.11%.Furthermore,a novel double-emission phenomenon(?_ex=365 nm:?_em?580 nm;?_ex=325 nm:?_em?505 nm)of Cs₂AgInCl₆at cryogenic temperatures(20 K)was discovered.This phenomenon explains the shoulder emission problem of 400–450 nm at room temperature and clarifies the luminescence mechanism of Cs₂AgInCl₆.Cs₂K_xAg_0.6Na_0.4In_0.8Bi_0.2Cl₆Br_xmicrocrystals were further developed based on the increase of PLQY of Cs₂AgInCl₆to 86%by doping Na⁺and Bi³⁺.Blue light excitation and narrow spectrum emission at low temperature are realized.By measuring the PL intensity,peak energy,FWHM,PLE and fluorescence lifetime under different temperature,the essence of blue light excitation is systematically studied.K⁺and Br^-dopants form a transitional nonlocalized donor energy level,which changes the exciton excitation and transition process.Cs₂K_xAg_0.6Na_0.4In_0.8Bi_0.2Cl₆Br_xand Cs₂K_xAg_0.6Na_0.4In_0.8Bi_0.2Cl₆I_xmicrocrystals were synthesized by solid phase pressing method.The newly developed materials can emit pure orange and red light under blue light at room temperature.By fitting the temperature-dependent PL,the essential difference between KBr and KI doping types in emission is studied.Pure color luminescence is expected to greatly promote the research progress of lead-free perovskite in the field of display devices.