Factors influencing self-trapped exciton emission of low-dimensional metal halides

Organic-inorganic hybrid metal halides (MHs) are widely used in the field of photoelectricity due to their excellent structure and photoelectric tunability. When separating inorganic metal halides by larger organic cations in crystals, multiple low-dimensional MHs (LDMHs) at the molecular level can be constructed, including two-dimensional (2D) layers, one-dimensional (1D) chains, and zero-dimensional (0D) clusters assembled by octahedral metal halide units. These LDMHPs exhibit significantly different luminescence properties from 3D MHs, which stem from the radiative recombination of self-trapped excitons (STEs) or the defect states. Along with the structure dimensions, the degree of intrinsic and instantaneous structure distortions greatly affects the STE broadband emission of LDMHs. Furthermore, molecular engineering such as the choice of organic cations, electron-phonon coupling effect, external temperature and pressure, and metal ion doping can greatly change the luminescence properties of LDMHs. Herein, we summarize and discuss the factors influencing the STE emission of LDMHs for a better understanding and to prospect the development of LDMHs in future.