Photoluminescence Tuning And Application Of 4d¹⁰ Low-dimensional Metal Halide Materials By Composition Engineering

In recent years,metal-halide perovskite materials（ABX₃）have attracted the attention of researchers due to their numerous advantages such as adjustable band gap,high photoluminescence quantum yield（PLQY）,wide gamut and low production cost.Lead-based perovskite materials are particularly notable for their excellent optoelectric properties among these materials;however,their toxicity and instability have hindered their development.To overcome this issue,researchers are seeking alternatives to lead that can provide comparable optoelectric properties.It has been proved that the ns² ions close to lead could exhibit comparable optical properties to the Pb²⁺ions.However,it remains to be studied whether the4d¹⁰ ions,which are also close to lead in the periodic table,can have similar properties.Additionally,ionic doping or reduing the dimensionality of perovskite can adjust the bandgap,achieve the minimum nonradiative recombination,enhancing the tolerance of material to defects,and improving stability and PLQY of materials under the ambient environment.In this thesis,the low-dimensional metal halides were synthesized by looking for alternative elements around lead in the periodic table of elements.Keeping the A-site ion with Cs⁺and the X-site ion with Cl^-in a 2:1 stoichiometric ratio of A to B-site ions,we focused on synthesizing low-dimensional metal halides by using alternative elements around lead and selecting 4d¹⁰ ions as the B-site ions.The relationship between structure and properties and the central ions of 4d¹⁰ was explored.After excluding the toxic cadmium element,the low-dimensional tin-based,indium-based and silver-based metal halides were studied by solvent engineering and doping methods.The main work in this thesis is summarized as follows:（1）Zero-dimensional Cs₂Sn Cl₆ crystals were synthesized in concentrated hydrochloric acid by cooling crystallization method,which exhibited no apparent photoluminescence phenomenon under UV irradiation at 365 nm or 395 nm.However,after doping with bismuth chloride（Bi Cl₃）and antimony chloride（Sb Cl₃）,blue(Cs₂Sn Cl₆:Bi_0.2)and yellow(Cs₂Sn Cl₆:Sb_0.2)emission were observed,respectively.The PLQY of Cs₂Sn Cl₆:Bi_0.2 and Cs₂Sn Cl₆:Sb_0.2could reach 40.91%and 8.76%,respectively.When the dose of doping was controlled to a certain amount,the photoluminescence（PL）of the crystals could be continuously adjusted from blue to red with the change of the relative doping content of Bi³⁺and Sb³⁺.What’s more,the Cs₂Sn Cl₆:Bi_0.08Sb_0.12 crystals in the codoped system could exhibited a dynamic excitation-dependent dual-emission phenomenon.Further more,the X-ray powder diffraction and PL spectra results indicated that the luminescence intensity and crystallinity of the materials remained relatively unchanged even after immersing the crystals in various solvents for a week.Additionally,thermogravimetric analysis demonstrated that the doping process increased the decomposition temperature of the crystals,enhancing their thermal stability.Therefore,this excitation-dependent dual emission luminescent material with high stability could be applied in the research of optical anti-counterfeiting technology.（2）Zero-dimensional crystals（CsInCl₅（H₂O）-orange）were synthesized in concentrated hydrochloric acid by cooling crystallization method.Under UV light at 254 nm,the crystals exhibited slight orange emission.Unlike the classical zero-dimensional metal halide structure,the central In³⁺in the inorganic octahedral not only coordinates with five Cl^-,but also has a coordinated H₂O molecule.Therefore,we speculated that the water molecules in the solvent may affect the nucleation and growth of crystals.To test this hypothesis,the CsInCl₅（H₂O）-orange crystals were dissolved in deionized water.After evaporation,we obtained zero-dimensional CsInCl₅（H₂O）-blue crystals,which can exhibit bright blue emission under UV light at 254 nm.The CsInCl₅（H₂O）-blue crystals showed cell contraction relative to CsInCl₅（H₂O）-orange.What’more,the photoluminescence lifetime of CsInCl₅（H₂O）-blue crystals is extremely long,up to 52.98 ms,and the PLQY of the crystals was increased from 2.25%to 11.61%.Additionally,in order to compare the influence to photoluminescence between pre-doping and post-doping method,Mn Cl₂ was introduced as a dopant.In the traditional cooling crystallization method,the obtained crystals（Mn-doped）still exhibited slight orange emission under UV light at 254 nm.Different from the pre-doping method,the crystals（Mn-post doped）obtained from the post-doping method showed the characteristic red emission of Mn²⁺under UV light at 254 nm,which demonstrated the effectiveness of the post-doping method to Mn²⁺.（3）From the previous experimental results,we found that the solvent can significantly impact the nucleation and growth of crystals.By cooling crystallization method,the one-dimensional Cs₂Ag Cl₃ crystals can be obtained in N,N-dimethylformamide（DMF）and the two-dimensional Cs Ag Cl₂crystal can be obtained in dimethyl sulfoxide（DMSO）.Both Cs₂Ag Cl₃ and Cs Ag Cl₂ exhibited bright yellow emission under UV light at 254 nm,the PLQY of which were 28.46%and 20.61%,respectively.This is because the stronger quantum confinement effects and higher exciton binding energy for Cs₂Ag Cl₃.In an effort to investigate the mechanism behind dimensional changes,N,N-dimethylacetamide（DMAC）and 1,3-Dimethyl-Tetrahydropyrimidin-2（1H）-one（DMPU）were also employed as solvents for comparison.It was found that one-dimensional Cs₂Ag Cl₃ can be obtained in DMAC,while two-dimensional Cs Ag Cl₂ can be obtained in DMPU.After analyzing the functional groups,dielectric constant and Goodman donor number（coordination ability）of the four solvents,we concluded that the coordination ability of the solvents played a crucial role in the regulation of the low-dimensional silver halides,providing a new perspective for the directed synthesis of metal halides.（4）Based on the previous three chapters,the structure of metal halides formed by 4d¹⁰ions is studied systematically in this chapter.It is found that the structural dimension of these crystals is positively correlated with the length of B-Cl bond.This phenomenon can be explained by the theory of Hard-Soft-Acid-Base.Combined with it,the structural dimensions of metal halide crystals can be accurately tuning.At the same time,the PLQY of crystals is affected not only by the crystal structures,but also by the internal defects.This research provides significant instruction for the design and directional synthesis of metal halide crystals.