Pressure‐Induced Emission (PIE) and Phase Transition of a Two‐dimensional Halide Double Perovskite (BA)₄AgBiBr₈ (BA=CH₃(CH₂)₃NH₃⁺)

Abstract

Two‐dimensional (2D) halide perovskites have attracted significant attention due to their compositional flexibility and electronic diversity. Understanding the structure–property relationships in 2D double perovskites is essential for their development for optoelectronic applications. In this work, we observed the emergence of pressure‐induced emission (PIE) at 2.5 GPa with a broad emission band and large Stokes shift from initially nonfluorescent (BA)4AgBiBr8 (BA=CH3(CH2)3NH3+). The emission intensity increased significantly upon further compression up to 8.2 GPa. Moreover, the band gap narrowed from the starting 2.61 eV to 2.19 eV at 25.0 GPa accompanied by a color change from light yellow to dark yellow. Analysis of combined in situ high‐pressure photoluminescence, absorption, and angle‐dispersive X‐ray diffraction data indicates that the observed PIE can be attributed to the emission from self‐trapped excitons. This coincides with [AgBr6]5− and [BiBr6]3− inter‐octahedral tilting which cause a structural phase transition. High‐pressure study on (BA)4AgBiBr8 sheds light on the relationship between the structure and optical properties that may improve the material's potential applications in the fields of pressure sensing, information storage and trademark security.

Lead‐Free Halide Double Perovskites: Structure, Luminescence, and Applications

“…This PIE evolution is modulated by a synergistic effect of phase transition and structure distortion. [ 159,160 ] Pressure‐dependent XRD reveals a phase transition from cubic to tetragonal at ≈5.6 GPa. The phase transition allows coherent rotation of BiCl 6 and AgCl 6 octahedra with an opposite direction along the c ‐axis in the ab plane.…”

“…However, an obvious orange PIE occurs and enhances with a blueshifted PIE peak and narrowed FWHM after compression. [ 159 ] The PIE reaches maximum at 8.2 GPa and then quenches gradually. Pressure‐dependent XRD indicates a phase transition starting at 0.6 GPa.…”

Recent Advances and Optoelectronic Applications of Lead‐Free Halide Double Perovskites

“…Additionally, under a high pressure of 25 GPa, the band gap of (BA) 4 AgBiBr 8 is narrowed from 2.61 to 2.19 eV (Figure 4). [67] Similarly, the cubic structure of Cs 2 AgBiBr 6 NCs also transforms to a tetragonal system at 2.3 GPa, and the pressure‐dependent absorption demonstrates that the band gap changes from red‐ to blueshifts [68] …”

Pressure‐Suppressed Carrier Trapping Leads to Enhanced Emission in Two‐Dimensional Perovskite (HA)2(GA)Pb2I7

“…[8] Theo rganic-inorganic hybrid nature and soft lattices of halide perovskites make the pressure effects much more profound, especially for the variation of carrier trapping that is critical for optoelectronic properties. Recently,p ressure-induced emission in halide perovskites was proposed by Zou et al, [9] which is due to the notable changes in structures under pressure.S tudies on pressureinduced behaviors of 2D perovskites have recently begun and photoluminescence (PL) performance can be effectively adjusted by pressure, [10] but the relationship between carrier trapping and PL intensity has not been well understood. Furthermore,t he property evolution during decompression has rarely been examined, which is very important for ambient-pressure applications.I nt his work, we employ pressure to modulate the highly distorted 2D GA-based perovskite (HA) 2 (GA)Pb 2 I 7 .T he variations of optical and structural properties under high pressure were systematically investigated using in situ PL, UV/Vis absorption, Raman spectroscopy,a nd synchrotron X-ray diffraction (XRD), as well as first-principles calculations.N otably,w ef ound significantly enhanced emission and reduced carrier trapping in (HA) 2 (GA)Pb 2 I 7 under pressure.Wealso pay attention to the property changes during decompression as well as the difference of the sample before and after high-pressure treatments.…”