Karmakar Abhoy, Bernard Guy M, Pominov Arkadii, Tabassum Tarnuma, Chaklashiya Raj, Han Songi, Jain Sheetal K, Michaelis Vladimir K
Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
Department of Chemistry and Biochemistry, University of California─Santa Barbara, Santa Barbara, California 93106, United States.
J Am Chem Soc. 2023 Mar 1;145(8):4485-4499. doi: 10.1021/jacs.2c10915. Epub 2023 Feb 14.
Lead-free metal halide double perovskites are gaining increasing attention for optoelectronic applications. Specifically, doping metal halide double perovskites using transition metals enables broadband tailorability of the optical bandgap for these emerging semiconducting materials. One candidate material is Mn(II)-doped CsNaBiCl, but the nature of Mn(II) insertion on chemical structure is poorly understood due to low Mn loading. It is critical to determine the atomic-level structure at the site of Mn(II) incorporation in doped perovskites to better understand the structure-property relationships in these materials and thus to advance their applicability to optoelectronic applications. Magnetic resonance spectroscopy is uniquely qualified to address this, and thus a comprehensive three-pronged strategy, involving solid-state nuclear magnetic resonance (NMR), high-field dynamic nuclear polarization (DNP), and electron paramagnetic resonance (EPR) spectroscopies, is used to identify the location of Mn(II) insertion in CsNaBiCl. Multinuclear (Na, Cl, Cs, and Bi) one-dimensional (1D) magnetic resonance spectra reveal a low level of Mn(II) incorporation, with select spins affected by paramagnetic relaxation enhancement (PRE) induced by Mn(II) neighbors. EPR measurements confirm the oxidation state, octahedral symmetry, and low doping levels of the Mn(II) centers. Complementary EPR and NMR measurements confirm that the cubic structure is maintained with Mn(II) incorporation at room temperature, but the structure deviates slightly from cubic symmetry at low temperatures (<30 K). HYperfine Sublevel CORrelation (HYSCORE) EPR spectroscopy explores the electron-nuclear correlations of Mn(II) with Na, Cs, and Cl. The absence of Bi correlations suggests that Bi centers are replaced by Mn(II). Endogenous DNP NMR measurements from Mn(II) → Cs (<30 K) reveal that the solid effect is the dominant mechanism for DNP transfer and supports that Mn(II) is homogeneously distributed within the double-perovskite structure.
无铅金属卤化物双钙钛矿在光电子应用中越来越受到关注。具体而言，使用过渡金属对金属卤化物双钙钛矿进行掺杂能够实现这些新兴半导体材料光学带隙的宽带可定制性。一种候选材料是锰（II）掺杂的CsNaBiCl，但由于锰负载量低，人们对锰（II）在化学结构上的插入性质了解甚少。确定掺杂钙钛矿中锰（II）掺入位点的原子级结构对于更好地理解这些材料的结构-性能关系从而推动其在光电子应用中的适用性至关重要。磁共振光谱法特别适合解决这一问题，因此采用了一种全面的三管齐下策略，包括固态核磁共振（NMR）、高场动态核极化（DNP）和电子顺磁共振（EPR）光谱法，以确定锰（II）在CsNaBiCl中的插入位置。多核（钠、氯、铯和铋）一维（1D）磁共振光谱揭示了锰（II）的掺入水平较低，部分自旋受到锰（II）相邻原子引起的顺磁弛豫增强（PRE）的影响。EPR测量证实了锰（II）中心的氧化态、八面体对称性和低掺杂水平。互补的EPR和NMR测量证实，在室温下掺入锰（II）时立方结构得以保持，但在低温（<30 K）下结构略微偏离立方对称性。超精细子能级相关（HYSCORE）EPR光谱法探究了锰（II）与钠、铯和氯之间的电子-核相关性。未发现铋的相关性表明铋中心被锰（II）取代。从锰（II）→铯（<30 K）的内源性DNP NMR测量表明，固体效应是DNP转移的主要机制，并支持锰（II）在双钙钛矿结构中均匀分布。
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