Triangulating Dopant-Level Mn(II) Insertion in a Cs₂NaBiCl₆Double Perovskite Using Magnetic Resonance Spectroscopy

Abstract

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 Cs 2 NaBiCl 6 , 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 Cs 2 NaBiCl 6 . Multinuclear ( 23 Na, 35 Cl, 133 Cs, and 209 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 23 Na, 133 Cs, and 35 Cl. The absence of 209 Bi correlations suggests that Bi centers are replaced by Mn(II). Endogenous DNP NMR measurements from Mn(II) → 133 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.

Alkali Tin Halides: Exploring the Local Structure of A2SnX6 (A = K, Rb; X = Cl, Br, I) Compounds Using Solid-State NMR and DFT Computations

“…Finally, the 119 Sn NMR linewidths for all cation-substituted materials (K, Rb, and Cs) increase as the halogen atoms are exchanged from Cl → Br → I. This increase in linewidth is likely due to J -coupling between 119 Sn and the directly bonded halogens that has been reported in similar materials. − …”

“…4.5 kHz with a lineshape indicating the presence of CSA. Upon slow MAS ( v r = 5 kHz) (Figure b), a second-order quadrupolar lineshape emerges, which is indicative of perturbation of the local electric field gradient (EFG) about the A-site. , To extract the experimental quadrupolar and CSA parameters for 39 K in K 2 SnBr 6 , the nonspinning and MAS spectra were first fit using the parameters predicted by periodic DFT computations. The predicted quadrupole coupling constant ( C Q ) and asymmetry parameter (η) are 0.77 MHz and 0.54, respectively, while the CSA is predicted to have Ω = 26 ppm and κ = −0.02.…”

Effect of aliovalent bismuth substitution on structure and optical properties of CsSnBr3

“…Although challenging, 209 Bi NMR is gaining attention as a sensitive method to probe solids 71 , 72 . For example, in double perovskites, it has been used to examine ion substitution in Mn-Cs 2 NaBiCl 6 73 , Cs 2 (Bi 1– x In x )AgCl 6 74 , and Cs 2 AgBiBr 6 75 ; in these cases, the [BiX 6 ] 3− octahedra are rather symmetrical, which limits the broadening induced by quadrupolar coupling. The 15% Bi-substituted sample was chosen for study because it offers the highest sensitivity.…”

Room-temperature synthesis of Ag- and Mn-doped Cs2NaBiCl6 octahedrons for dye photodegradation

“…Karmakar et al realized Mn 2+ doping in CNBC in the presence of concentrated HCl solvent at 120 °C. 34 Yao et al have reported a colloidal synthetic approach for Ag-, Mn- and Er-doped CNBC nanocrystals by reacting the corresponding metal acetate precursors with trimethylsilyl chloride under a nitrogen atmosphere at 230 °C. 35 However, most of the previous synthetic approaches for ion-doped CNBC usually involved organic ligands, relatively complicated procedures, or harsh conditions ( e.g.…”