Hexagonal Halide Perovskite Cs 2 LiInCl 6 : Cation Ordering, Face-Shared Octahedral Trimers and Mn 2+ Luminescence.

The In-based double perovskite halides have been widely studied for promising optical-electric applications. The halide hexagonal perovskite Cs 2 LiInCl 6 was isolated using solid-state reactions and investigated using X-ray diffraction and solid-state NMR spectra. The material adopts a 12-layered hexagonal structure (12R) consisting of layered cationic orders driven by the cationic charge difference and has Li + cations in the terminal site and In 3+ in the central site of face-shared octahedron trimers. Such a cationic ordering pattern is stabilized by electrostatic repulsions between the next-nearest neighboring cations in the trimers. The LiCl 6 octahedron displays large distortion and is confirmed by 7 Li SS NMR in the Cs 2 LiInCl 6 . The Cs 2 LiInCl 6 material has a direct bandgap of ~4.98 eV. The Cs 2 LiInCl 6 : Mn 2+ displays redshift luminescence (centered at ~610-622 nm) from the substituted Mn 2+ emission in octahedron with larger PLQY (17.8 %-48 %) compared with that of Cs 2 NaInCl 6 : Mn 2+ . The Mn-doped materials show luminescent concentration quenching and thermal quenching. The composition Cs 2 Li 0.99 In 0.99 Mn 0.02 Cl 6 exhibits the highest PL intensity, a maximum PLQY of 48 %, and high luminescent retention rate of ~86 % below 400 K and is suitable for application for pc-LED. These findings contribute to our understanding of the chloride perovskites and hold potential for widespread optical applications.