Synthesis Of Sb³⁺-doped Cd And Sn Chloride Perovskite Materials And Study Of Their Luminescence Mechanism

In the last decade or so,perovskite materials have broad application prospects in solar cells,electroluminescence,photodetectors and other fields due to their own advantages,such as high luminescence quantum yield,high mobility,adjustable band gap,solution-processable and other advantages,and are the current research hotspots of new functional materials.Although the traditional Pb-based perovskite materials have better performance,their application is limited by the toxicity of Pb itself.The development of non-lead high performance perovskite materials has gradually become a trend.In addition,the effect of spatial microscopic effects on the luminescence behavior can further investigate the luminescence mechanism of similar materials.To address the above hotspots and difficulties,this paper presents an in-depth study of Sb³⁺-doped modified halide substrates and their luminescence behaviour,mainly by chemically doping Sb³⁺ions into different substrates and regulating their luminescence properties through microscopic interactions;Sb³⁺ion doping,on the one hand,allows us to understand the effect of electrophonon coupling and spin-orbit coupling in the doped system on the internal relaxation process.On the other hand,understanding the radiation mechanism and regulation of the luminescence centre due to the single or trilinear state of Sb³⁺allows us to further develop the use of similarly doped materials for a wider range of applications in optoelectronic devices in the future.The specific research work is as follows.（1）We have synthesised a series of Sb³⁺-doped Rb Cd Cl₃ crystal powders by a simple hydrothermal method and have investigated their structural and optical properties.Sb³⁺-doped Rb Cd Cl₃ powder has a typical crystal structure and is connected by octahedral ribs.It exhibits highly efficient yellow luminescence at about 596 nm,with a large Stokes shift and a wide emission band,and a photoluminescence quantum yield（PLQY）of up to 91.7%.This is due to the Sb³⁺doping effectively reducing its band gap and increasing its band-side absorption coefficient,in addition to the effective electron-phonon coupling,which induces the conversion of its band-side single-and triple-linear states to their respective self-captured excitons（STE1）,enhanced by increasing temperature,with only the triple-linear self-bound excitons emitting at room temperature,demonstrating that all its high-energy single-linear self-bound excitons are converted to the triple-linear self-bound states,However,its emission colour becomes white at low temperatures because the single-linear state self-trapping exciton（STE0）can also exist stably or booster at low temperatures,emitting short-wavelength blue luminescence;and the combination of blue and yellow light forms white luminescence.Due to the temperature-dependent colour of the luminescence,it can be used in temperature sensors.（2）We also obtained Sb³⁺ doped Rb₃Cd₂Cl₇ by a simple hydrothermal method.The structure of Rb₃Cd₂Cl₇ consists of layers stacked up,each layer consisting of two identical bilayers,where each small layer consists of[Cd Cl₆]^4-connected by dots in the same plane of growth to obtain the material as green luminescence,with an emission peak at 525 nm with a half peak width of the maximum efficiency of the sample produced was 57.47%with a Stokes shift of200 nm at 115 nm.Compared with the above material,although the composition of the two elements are the same,the structure of the prismatic connection into a point connection,from the chain into a planar structure,point connection reduces the interaction between the small range of luminescent centres,the double layer of planar structure will lead to their mutual quantum confinement effect becomes stronger,thus enhancing the electro-phonon coupling effect,reducing the triplet state STE1 of the deployment,and ultimately will lead to a relative reduction inefficiency.And through further research and analysis,we found that the two-phonon effect,is related to the formation of the self-bound state;the luminescence principle of the material is mainly from the process of ¹S₀→³P₁,the whole process can be summarized as under the excitation of 325 nm UV light,the Sb ion is excited from the ¹S₀ excited state to the ³P₁ excited state,and then enters the self-bound state through the electro-phonon coupling;due to the inter-octahedral domain-limiting affect the in-band.The spin-orbit coupling is relatively weakened due to the inter-octahedral confinement effect,so its self-bound state energy level position is slightly higher relative to the previous sample,producing green light emission.（3）Sb-doped Rb₂SnCl₆ powder materials were prepared by a simple hydrothermal method.The synthesized material obtained red light emission at 677nm with partial NIR emission under the excitation of 355 nm UV light,and the luminescence peaks were characterized by a wide luminescence bandwidth and a large Stokes shift with a PLQY of 9.02%.It was found that the luminescence of Sb³⁺-doped Rb₂SnCl₆ is also mainly related to the exciting self-bound exciton state of Sb ions.The double phonon effect supports the generation of the self-bound state,and the sample exhibits a double peak at low temperatures because the self-bound exciton（STE1）at room temperature comes from the ¹S₀-³P₁excitation in Sb³⁺and undergoes a dynamic Jahn-Teller distortion and then the distorted ³P₁ undergoes a fast non-radiative relaxation from the high-energy state to the self-bound state,while the STE0 at low temperatures is mainly related to the relaxation rate and the high-energy energy level self-bound state Bouguer number.The apparent redshift of the luminescence in this regime comes from the fact that the strong spin-orbit coupling of Sb interacts somewhat with the strong spin-orbit coupling of Sn,which further drives the redshift of the self-bound state through electron correlation effects and electro-phonon coupling effects in the strong confinement domain.This thesis focuses on the effect of the energy band structure of Sb³⁺-doped perovskite systems on photophysical properties,targeting the modulation of the interaction of spin-orbit coupling,electro-phonon coupling and local space-limited effects,providing its insights into the luminescence tuning and intensity modulation of related compounds,and also offering new ways to design lead-free and non-toxic near-infrared luminescent materials for optoelectronic applications and their applications.