Study of Structural Phase Transition and Optical Properties in a Series of New 0D Hybrid Metal Halides: (3,5-DMP)2Bi1-xSbxCl5

Abstract

Low-dimensional organic-inorganic metal halides (OIMHs) have garnered immense attention and extensive research in the field of solid-state lighting materials owing to their outstanding self-trapped exciton (STE)-induced luminescence properties. [1] Though there has been significant research activity in the field of lead-based hybrid metal halides, these compounds suffer from environmental toxicity and atmospheric instability. [2,3] Thus, it is significant to explore new and promising materials, containing non-toxic elements with excellent atmospheric stability and superior luminescence properties. This has led to the dawn of Bi/Sb-based OIMHs as potential substitutes for lead-based OIMHs with very good thermal and ambient stability and containing relatively less toxic and earth-abundant elements, which are crucial for large-scale commercial use. [4,5] Further, it has been observed that reduction in the dimensionality of the Bi/Sb-based OIMHs enhances their photoluminescence (PL) properties for applications in solid-state lighting devices. Moreover, understanding the relationship between the structure and luminescence properties of these materials is of utmost importance for tuning the PL properties for various practical applications. To further explore the 0D lead-free hybrid metal halides, herein we report two novel organic ammonium-based 0D lead-free metal halides, (3,5-DMP)2BiCl5 and (3,5-DMP)2SbCl5 (3,5-DMP = 3,5- dimethylpiperidine) that crystallize in the triclinic system with P space group and monoclinic system with P21/c space group, respectively. The crystal structure consists of discrete isolated [M2Cl10] 4− (M = Bi, Sb) inorganic units encased by (3,5-DMP)+ organic cations as confirmed by single crystal study. The structural phase transition from triclinic to monoclinic phase is further studied through the synthesis of solid solution, (3,5-DMP)2Bi1−xSbxCl5, by the substitution of Sb at Bi crystallographic site in the pristine Bi compound. The effect of the structural phase transition on the optical properties like optical band gap, PL characteristics is also studied. The compounds are further studied by various characterization techniques. [6]