Pressure-Induced Free Exciton Emission in a Quasi-Zero-Dimensional Hybrid Lead Halide.

Abstract

Structural dimensionality and electronic dimensionality play a crucial role in determining the type of excitonic emission in hybrid metal halides (HMHs). It is important but challenging to achieve free exciton (FE) emission in zero-dimensional (0D) HMHs based on the control over the electronic dimensionality. In this work, a quasi-0D HMH (C7 H15 N2 Br)2 PbBr4 with localized electronic dimensionality is prepared as a prototype model. With increasing pressure onto (C7 H15 N2 Br)2 PbBr4 , the broad and weak self-trapped exciton (STE) emission at ambient conditions is considerably enhanced before 3.6 GPa, which originates from more distorted [PbBr4 ]2- seesaw units upon compression. Notably, a narrow FE emission in (C7 H15 N2 Br)2 PbBr4 appears at 3.6 GPa, and then this FE emission is gradually strengthened up to 8.4 GPa. High pressure structural characterizations reveal that anisotropic contraction of (C7 H15 N2 Br)2 PbBr4 results in a noticeable reduction in the distance between adjacent [PbBr4 ]2- seesaw units, as well as an obvious enhancement of crystal stiffness. Consequently, the electronic connectivity in (C7 H15 N2 Br)2 PbBr4 is sufficiently promoted above 3.6 GPa, which is also supported with theoretical calculations. The elevation of electronic connectivity and enhanced stiffness together lead to pressure-induced FE emission and subsequent emission enhancement in quasi-0D (C7 H15 N2 Br)2 PbBr4 .