Luminescent Properties And Application Research Of Rare Earth Doped Double Perovskite Cs₂Ag_1-xNa_xBiCl₆

Luminescent materials are the supporting materials for information display,optoelectronic devices,biomedicine,and other fields.The development and utilization of new luminescent materials have significant value for social development and technological progress.Lead-based halide perovskite materials（ABX₃,where A and B are different cations,and X is a halide ion）have flexible lattice structure and adjustable electronic structure.They exhibit high absorption coefficient,wide spectral response range,long carrier lifetime,and high photoelectric conversion efficiency.They have broad application prospects in LED lighting,display technology,optoelectronic conversion devices,and photocatalysis.However,the poor water,oxygen,and thermal stability of lead-based halide perovskite materials,as well as the toxicity of lead,seriously restrict their commercial application.By replacing two divalent lead ions(Pb²⁺)with a monovalent and a trivalent metal cation(B⁺and B³⁺),a double perovskite with the chemical formula A₂B_ⅠB_ⅡX₆can be obtained.Metal halide double perovskite materials have good stability and avoid the toxicity of lead.The study and application of their photoelectric properties have attracted widespread attention.Ion doping is an effective method to regulate the optical properties of materials.The double perovskite structure has an octahedral lattice with six coordination numbers,providing good support for doping.Rare earth ions(RE³⁺,such as Ho³⁺,Pr³⁺,Tm³⁺,Er³⁺,Yb³⁺,and Nd³⁺)have unique energy level structures.Their emission peaks cover visible to near-infrared light,providing rich luminescence.However,more exploration is needed for the luminescent properties and application research based on rare earth-doped double perovskite materials.For example:How to regulate the luminescence process of rare earth ions in double perovskite matrices?How to obtain more efficient near-infrared luminescence in double perovskite materials?How to achieve multi-mode anti-counterfeiting based on a single double perovskite matrix?And so on.Here,we selected the double perovskite Cs₂Ag_1-xNa_xBiCl₆material as the matrix and conducted exploratory research on luminescence property regulation and application through rare earth ion doping.The specific work content is as follows:（1）By co-doping with different RE³⁺ions(Eu³⁺/Yb³⁺/Tb³⁺)and Er³⁺ions in a double perovskite,an effective approach to enhance the near-infrared（NIR）emission of Er³⁺at 1540 nm was explored.In Cs₂Ag_0.1Na_0.9BiCl₆double perovskite（DPs）as the matrix,the dual doping（Eu-Er,Tb-Er,and Yb-Er）could respectively enhance the 1540 nm emission of Er³⁺in DPs through the cross-relaxation（CR）between Eu³⁺(Tb³⁺)and Er³⁺ions or the energy transfer（ET）between Yb³⁺and Er³⁺ions.For the triple doping（DPs-Yb-Eu-Er and DPs-Yb-Tb-Er）samples,the CR process between Eu³⁺(Tb³⁺)and Er³⁺ions and the ET process between Yb³⁺and Er³⁺ions could synergistically enhance the 1540 nm emission of Er³⁺.Under excitation at 365 nm and 980 nm,the 1540 nm emission of DPs-Yb-Eu-Er was 6.2 and 45 times higher than that of DPs-Er,respectively.The photoluminescence quantum yield（PLQY）of DPs-Yb-Eu-Er under 365nm excitation was 18.2%,which was the highest efficiency among micrometer-sized double perovskites.A near-infrared LED device based on DPs-Yb-Eu-Er was fabricated and demonstrated good night vision imaging and tissue penetration capability.（2）By regulating the upconversion luminescence properties of rare earth-doped Cs₂Ag_1-xNa_xBiCl₆,a highly efficient luminescent material applicable for multi-mode anti-counterfeiting was developed.By adjusting the feeding ratio of Ag⁺and Na⁺ions and the doping concentration of rare earth ions,Cs₂Ag_0.4Na_0.6BiCl₆-Yb-Er upconversion luminescent material was obtained,which emitted green light under excitation at 980 nm,808 nm,and 1540 nm.The optimal Cs₂Ag_0.2Na_0.8BiCl₆-Yb-Tm and Cs₂Ag_0.2Na_0.8BiCl₆-Yb-Ho upconversion luminescent materials emitted purple and white light,respectively,under excitation at 980 nm.Under excitation at 365 nm,Cs₂Ag_0.4Na_0.6BiCl₆-Yb-Er emitted yellow light,while Cs₂Ag_0.2Na_0.8BiCl₆-Yb-Tm and Cs₂Ag_0.2Na_0.8BiCl₆-Yb-Ho emitted orange-red light.Meanwhile,Yb³⁺ions enabled all three materials to have good NIR emission properties.Finally,by using the characteristic differences in the luminescence properties of the materials with different doping types,excitation wavelengths,and excitation powers,the"horse"and"HENU"patterns were fabricated,which had multiple anti-counterfeiting functions with dual-mode excitation of multi-color luminescence,variable-power excitation of multi-color patterns,and region of visible and NIR luminescence.