邵 山¹，徐 帆¹，曹丙强²

（1. 曲阜师范大学 物理工程学院，山东 济宁 273165；2. 济南大学 材料科学与工程学院，山东 济南 250022）

引用格式：

DOI：10.13732/j.issn.1008-5548.2024.03.012

收稿日期：2023-11-25，修回日期：2024-02-12，上线日期：2024-04-16。

基金项目：国家自然科学基金项目，编号：51872161；国家重点研发计划项目，编号：2022YFC3700801。

第一作者简介：邵山（1998—），女，硕士生，研究方向为无铅双钙钛Cs₂AgInCl₆制备技术。E-mail：17562054912@163. com。

通信作者简介：曹丙强（1978—），男，博士，教授，山东省泰山学者海外特聘专家，博士生导师，研究方向为半导体材料与器件。E-mail：mse_caobq@ujn.edu.cn。

摘要：【目的】 分析不同表面配体修饰对无铅双钙钛矿 Cs₂AgInCl₆量子点稳定性和光学性能的影响，实现量子点稳定性和光学性能的提升。【方法】 通过热注射方法合成Cs₂AgInCl₆量子点，在合成过程中原位引入长碳链的油酸（OA）和有2条短支链的2-己基癸酸（DA），研究不同表面配体修饰对Cs₂AgInCl₆量子点的纯度、粒径和形貌的影响，并对量子点进行荧光性、稳定性分析以及发光机制的讨论。【结果】 OA配体和DA配体均匀覆盖Cs₂AgInCl₆量子点表面，2种量子点均呈现钙钛矿的立方结构，具有良好分散性和高结晶度，在常温环境中连续储存80 d后，DA修饰的Cs2AgInCl6量子点仍能保持初始发光的 95. 43%，荧光量子产率为 4. 67%。【结论】 DA配体可以保持 Cs₂AgInCl₆量子点的稳定性，并有助于有效的辐射复合，利于新兴的无铅双钙钛矿Cs₂AgInCl₆量子点的光电用。

关键词：量子点；无铅双钙钛矿；表面配体；稳定性

Abstract

Objective In contrast to toxic lead-based perovskites， non-toxic and optically superior lead-free double perovskite Cs₂AgInCl₆quantum dots have garnered significant attention. However， challenges arise from the poor stability and tendency to aggregate in air， hindering their practical applications. To address these issues， this study analyzes the effects of various surface ligand modi⁃fications on the stability and optical properties of Cs₂AgInCl₆ quantum dots， resulting in improved stability and optical characteristics. The research methodologies and findings presented in this paper hold promise for the application of double perovskite Cs₂AgInCl₆ quantum dots in optoelectronic devices.

Methods Cs₂AgInCl₆ quantum dots were synthesized using a thermal injection method， with oleic acid （OA） and 2-hexylcapric acid （DA） as surface ligands. The synthesized quantum dots underwent comprehensive characterization including powder diffraction， Fourier infrared spectrometry， transmission electron microscopy， transmission， reflection， and absorption spectrometry， stability assessment， and transient fluorescence spectrometry. The influence of different surface ligand modifications on the purity， particle size， and morphology of Cs₂AgInCl₆ quantum dots was investigated， along with fluorescence and stability analyses. Furthermore， the luminescence mechanism was elucidated through examinations of low-temperature fluorescence，power-dependent fluorescence， and circular polarization luminescence properties.

Results and Discussion The impact of different surface ligand modifications on the purity， particle size， and morphology of Cs₂AgInCl₆ quantum dots was investigated. X-ray diffraction （XRD） analysis showed consistent results with the bulk standard card ICSD 1927876 for both types of quantum dots， indicating no impurity peaks. Cs₂AgInCl₆-DA quantum dots exhibited superior crystallization compared to Cs2AgInCl6-OA quantum dots， as evidenced by the 1 468cm-1peak for Cs₂AgInCl₆-OA and the 1 465 cm-1 peak for Cs₂AgInCl₆-DA， indicating tensile vibration characteristics of the—COO—group. Both types of quantum dots displayed a cubic structure， good dispersion， and high crystallinity of the perovskite. Fluorescence and stability analyses were conducted for Cs₂AgInCl₆ quantum dots. Cs₂AgInCl₆-DA quantum dots exhibited significantly higher luminescence intensity compared to Cs₂AgInCl₆-OA quantum dots， with a photoluminescence quantum yield of 4. 67%. After continuous storage at room temperature for 80 days， DA-modified Cs₂AgInCl₆ quantum dots retained 95. 43% of the initial luminescence，while Cs₂AgInCl₆-OA quantum dots exhibited a photoluminescence quantum yield of 2. 79%， with fluorescence intensity decreasing to 56. 27% after 80 days of continuous standing. The average lifetime of Cs₂AgInCl₆-OA and Cs₂AgInCl₆-DA quantum dots was determined to be 1. 236 9 ns and 3. 936 6 ns，respectively. The luminescence mechanism was discussed based on low-temperature fluorescence，power-dependent fluorescence，and circular polarization luminescence studies. Both types of quantum dots showed a decrease in emission intensity with increasing temperature，indicating inhibition of non-radiative recombination at lower temperatures. The exciton binding energy was calculated to be 64. 67 meV for Cs₂AgInCl₆-OA quantum dots and78. 88 meV for Cs₂AgInCl₆-DA. Photoluminescence peaks remained consistent for both types of quantum dots，but there were noticeable differences in luminous intensity. Additionally，a polarization value， defined as the ratio of the difference in left-handed and right-handed polarized photoluminescence intensities to their sum and normalized to the range ［-1，1］，was intro⁃duced as a measure of the degree of photoluminescence emission polarization. The polarization value，or DP value，was determined to be 5. 561% for Cs₂AgInCl₆-OA and5. 333% for Cs₂AgInCl₆-DA.

Conclusion Pure-phase Cs₂AgInCl₆-OA and Cs₂AgInCl₆-DA quantum dots were successfully synthesized via thermal injection.The hydroxyl group in the ligand binds to the surface of Cs₂AgInCl₆ quantum dots as—COO— groups，indicating uniform coverage of the long-branched OA ligand and short-branched DA ligand. Both Cs₂AgInCl₆-DA and Cs₂AgInCl₆-OA quantum dots exhibit a cubic structure with excellent dispersion and uniform size. Cs₂AgInCl₆-DA demonstrates superior performance compared to traditional Cs₂AgInCl₆-OA. When exposed to air for 80 days continuously，Cs₂AgInCl₆-DA maintains significant fluorescence，demonstrating remarkable stability. DA ligands effectively reduce surface defects of quantum dots and inhibit non-radiative recombination，resulting in longer fluorescence lifetimes and higher photoluminescence quantum yield. The longbranched OA and short-branched DA ligands control morphology and prevent agglomeration by modifying the surface of quantum dots. Free excitons transition from valence band maximum （VBM） to conduction band minimum （CBM）. Some free excitons undergo non-radiative recombination due to surface defects，while others are trapped by self-trapping states resulting from JahnTeller distortion of the ［AgCl₆］^5- octahedron under strong electron-phonon coupling. Radiative recombination of self-trapped excitons drives emission in the double perovskite Cs₂AgInCl₆. In summary，DA ligands contribute to maintaining the stability of Cs₂AgInCl₆ quantum dots and promoting effective radiation recombination，offering potential for the photoelectric application of emerging lead-free double perovskite Cs₂AgInCl₆ quantum dots.

Keywords：quantum dots； lead-free double perovskite； surface ligand； stability

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