Spin Centers in Vanadium-Doped Cs<sub>2</sub>NaInCl<sub>6</sub> Halide Double Perovskites
Kunpot Mopoung, Anna Dávid, Xianjie Liu, Mats Fahlman, I. A. Buyanova, Weimin Chen, Yuttapoom Puttisong
Abstract
High Resolution Image Download MS PowerPoint Slide We provide direct evidence for a spin-active V 4+ defect center, likely in the form of a VO 2+ complex, predominantly introduced in single crystals of vanadium-doped Cs 2 NaInCl 6 halide double perovskites grown by the solution-processed hydrothermal method. The defect has C 4 v point group symmetry, exhibiting an electron paramagnetic resonance (EPR) spectrum arising from an effective electron spin of S = 1/2 and a nuclear spin of I = 7/2 (corresponding to 51 V with nearly 100% natural abundance). The determined electron g -factor and hyperfine parameter values are g ⊥ = 1.973, g ∥ = 1.945, A ⊥ = 180 MHz, and A ∥ = 504 MHz, with the principal axis z along a ⟨001⟩ crystallographic axis. The controlled growth of V-doped Cs 2 NaInCl 6 in an oxygen-free environment is shown to suppress the V 4+ EPR signal. The defect model is suggested to have a VOCl 5 octahedral coordination, where one of the nearest-neighbor Cl – of V is replaced by O 2–, with octahedral compression along the V–O axis. This VO complex formation competes with the isolated V 3+ substitution of In 3+, which in turn provides a means for the charge-state tuning of V ions. This finding calls for a better understanding and control of defect formation in solution-grown halide double perovskites, which is critical for optimizing and tailoring material design for solution-processable optoelectronics and spintronics.