Luminescence And Application Of All-inorganic Matal Halide Perovskites By Rare Earth Controlled

The all-inorganic halide perovskite material has a variety of chemical formulas（ABX₃,and A₂B^ⅠB^ⅡX₆,where A and B are cations,and X is a halogen ion）,flexible lattice structure,adjustable electronic structure,etc.,showing unique optoelectronic properties,Such as large absorption cross section,good defect tolerance and long carrier diffusion radius.They have a wide range of applications in the fields of lighting,display,photovoltaic,photoelectric detection and anti-counterfeiting,and show good application prospects.However,the representative inorganic lead halide perovskite has poor water,oxygen and thermal stability,and the toxicity of lead,which severely limits its commercialization process.In addition,the double perovskite formed by the chemical formula A₂B^ⅠB^ⅡX₆ directly forms self-trapped exciton broadband emission,with relatively large band gap,and generally low fluorescence efficiency.Facing the various problems of inorganic metal halide perovskite materials,ion doping,and construction of composite structures are considered to be effective means to control the optoelectronic properties of functional materials.As a high-quality functional material,rare earth ions have unique optical and electrical properties.The transition of 4f electrons of rare earth ions between different energy levels produces a large number of up-conversion and down-transfer emission spectra.This provides a good basis for the design and synthesis of luminescent materials with specific properties.Based on this,this thesis takes the all-inorganic halide perovskite and rare-earth ion upconversion materials as the research object,with the aim of improving its stability,luminous efficiency and expanding its functionality.First,by constructing a composite structure combining rare earth ion-doped up-conversion nanoparticles and lead halide perovskite quantum dots,stable and effective dual-mode emission is realized and applied to security and anti-counterfeiting.Secondly,in view of the problems of large band gap of all-inorganic double perovskite,untunable spectrum and low fluorescence efficiency,the direct doping of rare earth ions not only realizes the spectral control of double perovskite,but also obtains excellent fluorescence emission of upconversion,and finally realize the dual-mode fluorescence emission directly.These works provide new research ideas for the development of all-inorganic halide perovskites,and provide experimental and theoretical basis for the development of multifunctional halide perovskite materials.The specific work content is summarized as follows:（1）A nanocomposite composed of NaYF₄:20%Yb/0.5%Tm@NaLuF₄ and CsPbCl₃:Mn was synthesized by silicon coating.This nano-material successfully realized the dual-mode luminescence emission under excitation 365 nm and 980 nm light sources.In addition,the NaYF₄:Yb/Tm@NaLuF₄@CsPbCl₃:Mn@SiO₂ composite material with a quasi-core-shell structure exhibits excellently stability.Furthermore,through transient fluorescence spectroscopy tests,it is concluded that both photon reabsorption and non-radiative energy transfer processes exist in the up-conversion mode,in which photon reabsorption dominates.Finally,the practical application value of this composite material were verified by an anti-counterfeiting experiment.The work in this paper provides new ideas for the application of multifunctional nanomaterials.（2）To achieve better recombination effect,we use the in situ growth method to grow lead halide perovskite quantum dots in SiO₂ mesopores with the help of mesoporous SiO₂-wrapped upconversion nanoparticles.Using this method,more CsPbBrI2 perovskite quantum dots can be encapsulated in SiO₂ mesopores,which is beneficial to produce better upconversion fluorescence effect and improve the stability of perovskite quantum dots.And,it should be emphasized that the upconversion nanoparticles used in this chapter are the core-shell-shell structure of NaYF₄@NaYF₄:Yb/Tm@NaYF₄:Yb/Nd.In this structure,the light-emitting layer is confined in the shell layer,which shortens the energy transfer distance between the sensitizer Yb³⁺ion and the activator Tm³⁺ ion,which is beneficial to improve the energy transfer efficiency.The NaYF₄:Yb/Nd absorber layer is wrapped on the surface of the light-emitting layer to avoid the direct contact between Yb³⁺/Nd³⁺and Tm³⁺ ions,which helps to maintain a high doping concentration of Yb³⁺/Nd³⁺.Compared with the traditional core-shell structure,this inert core/luminescent shell/sensitized layer structure significantly enhances the up-conversion luminescence under excitation at 808 and 980 nm.Moreover,since Tm³⁺ ions are doped in the shell,which reduces the distance between it and the perovskite quantum dots,through transient fluorescence spectroscopy tests,proves that the composite structure has a higher F?rster resonance energy transfer efficiency.（3）Based on the composite structure that plays the main role of rare earth ions and perovskite crystals,we choose Cs₂AgInCl₆ lead-free double perovskite with a more stable chemical structure as the matrix,and use an improved hydrothermal method to prepare rare earth Er³⁺ions directly doped Cs₂Ag_0.6Na_0.4InCl₆:Bi double perovskite single crystal.With the assistance of sodium ions,the high-efficiency upconversion green emission of Er³⁺ions under the excitation of 808,980 and 1540 nm multi-wavelength NIR was realized,and the optimal value of the upconversion fluorescence quantum yield was 0.17%.At the same time,a small amount of Bi³⁺ion doping can effectively promote the down-transfer fluorescence emission of Er³⁺ions,thereby adjusting the yellow light of the double perovskite single crystal to green light.In addition,in the down-shift model,high-efficiency NIR emission at 1540 nm can be obtained under excitation at 365,808,and 980 nm,and the maximum fluorescence quantum yield value is 38.35%.These excellent properties make double perovskite materials have great potential in optoelectronic applications.（4）The rare earth Ho³⁺ ions doped Cs₂AgIn_0.99Bi_0.01C16 double perovskite nanocrystals were synthesized by modified hot-injection method.Under the excitation of 365 nm light source,energy was transferred to Ho³⁺ions through the self-trapped excitons state（STEs）of double perovskite nanocrystals to produces fluorescence emission,and the purpose of transforming Cs₂AgIn_0.99Bi_0.01Cl₆ double perovskite from yellow light emission to red light was realized.By increasing the reaction time of the mixed solution,double perovskite sheets were obtained and the fluorescence quantum yield was improved.Finally,on this basis,the nanocrystals were continuously doped with rare earth Yb³⁺ions.Under the excitation of 980 nm laser,the red light emission of Ho³⁺ ions was also realized through the sensitization of Yb³⁺ ions.So far,it is the first time for us to obtain both up-conversion and down-transfer red emission in halide dual perovskite nanocrystals.（5）In addition to visible light,rare-earth ions-doped double perovskite nanocrystals also show excellent performance in the near-infrared region.We synthesized a series of lanthanide ions(Yb³⁺,Tm³⁺,Ho³⁺,Nd³⁺,Pr³⁺and Er³⁺)doped Cs₂AgIn_0.99Bi_0.01C16 double perovskite nanocrystals by thermal implantation.Under the excitation of near-ultraviolet light at 365 nm,lanthanide ions-doped Cs₂AgIn_0.99Bi_0.01C16 double perovskite nanocrystals not only exhibit broadband visible light emission,but also a series of highly efficient wavelength-tunable near-infrared emission from rare earth ions light emission.The quantum yield of the double perovskite nanocrystals in the visible light region from 400 to 800 nm is only about 10%,while the best quantum yield of near-infrared light emitted by rare earth ions is 56.7%.The total quantum yield value reaches 66.7%,which is the highest value reported so far in the field of double perovskite nanocrystals.More importantly,the near-infrared emission wavelengths of lanthanide ions-doped Cs₂AgIn_0.99Bi_0.01Cl₆ double perovskite nanocrystals include not only shorter wavelength near-infrared（≤900 nm）,but also more suitable for food analysis and medical diagnosis.Longer wavelength near-infrared light（>900nm）for applications.Finally,Cs₂AgIn_0.99Bi_0.01Cl₆ double perovskite nanocrystals with an optimal doping concentration of 11.2%Nd³⁺ions were embedded into a polymethacrylate（PMMA）polymer matrix（NCs@PMMA）,ensuring that Nd³⁺ions-based Stability of doped Cs₂AgIn_0.99Bi_0.01Cl₆ near-infrared LED devices.Under the illumination of the prepared near-infrared pc-LED,good night vision imaging and tissue penetration experiments were achieved.This work provides a new research idea for the development of efficient near-infrared nanomaterials.