Design And Optical Properties Of Lead-free Double Perovskite Multifunctional Materials Doped With Rare Earth Ions

Rare earth ion doped lead halide perovskite materials show great application potential in optoelectronic field because of their excellent optical properties.However,the toxicity and low stability of these materials greatly limit their commercial application prospects in the future.With the deepening of the research,the new double perovskite materials obtained by substituting two metal ions for lead ions not only retain the three-dimensional perovskite structure,but also maintain charge neutrality.It shows great potential in exploring new optoelectronic applications.In addition,multi-functional materials refer to high-performance materials that achieve two or more functions in a single material,which can greatly improve the utilization rate of materials,so as to better meet the needs of continuous development of production and life.To sum up,we chose the double perovskite material with stable environmental protection and excellent optical properties as the basis of the experiment.By doping different combinations of rare earth elements,the structure and up-conversion luminescence mechanism of the synthesized phosphors were explored in detail,and their potential applications in solid-state fluorescence and contactless temperature detection were explored.The detailed study includes the following two aspects:（1）Halide double perovskite Cs₂NaBiCl₆ was successfully synthesized by a simplified solvothermal method.The concentration quenching of high concentration activated ion Er³⁺was skillfully avoided by using the sufficient ion spacing of Bi³⁺ions in the[BiCl₆]^3-octahedron with double perovskite structure.In this paper,the mechanism of green up-conversion emission with high purity and high brightness after high concentration rare earth ion combination(Er³⁺-Yb³⁺/Nd³⁺)doping is explored in detail.The Cs₂NaBiCl₆:40%Er³⁺,20%Yb³⁺phosphor with the best luminous effect is successfully packaged into a pure green emission LED device.In the aspect of temperature detection,under the excitation of double near infrared wavelengths,the temperature sensing properties of ²H_11/2/⁴S_3/2 coupling ⁴I_15/2 of Er³⁺ions in three different(Er³⁺;Er³⁺-Yb³⁺;Er³⁺-Nd³⁺)phosphors were systematically discussed based on the fluorescence intensity ratio technique.In contrast,Cs₂NaBiCl₆:40%Er³⁺phosphors perform well,and their relative sensitivities are as high as 1.27%K^-1（980nm）and 1.57%K^-1（808 nm）.（2）Oxide double perovskite La₂MgTiO₆ was successfully synthesized by high temperature solid state method.From the XRD spectra and emission spectra of different rare earth element combinations,it can be seen that the oxide double perovskite La₂MgTiO₆ has excellent rare earth element compatibility,which can provide a suitable crystal field environment for a variety of rare earth elements and show excellent up-conversion luminescence.Based on this,we have constructed four different combinations of doping systems[Ln³⁺(Tm³⁺;Er³⁺;Ho³⁺;Tm³⁺/Er³⁺)-Yb³⁺].Through the rigorous analysis and comparison of the up-conversion emission spectra,we have selected the optimal doping concentrations in the above four systems and packaged into pure green,blue and near-white LED devices,which show great potential in solid-state fluorescence.The phosphor with excellent luminous properties is an ideal material for designing optical thermometers because it can eliminate the interference of the external environment to the maximum extent.Therefore,we use four kinds of doping systems to construct and analyze four ratio thermometer models（modeⅠ-Ⅳ:Tm-Yb;Er-Yb;Ho-Yb;Er/Tm-Yb）.Especially in mode IV,a new type of dual launch center self-calibrating zone thermometer based on Er/Tm is successfully designed,which can provide specific LIR for low temperature,medium temperature and high temperature regions,and finally obtain high relative sensitivity in ultra-wide temperature range.