H₂O-NH₄⁺-Induced Emission Modulation in Sb³⁺-Doped (NH₄)₂InCl₅·H₂O

Lead-based metal halide perovskites have received widespread attention for their promising application prospects in the field of lighting and display due to their excellent optical properties. However, the toxicity of lead may hinder their further commercial application. Herein, a zero-dimensional (0D) metal halide (NH₄)₂InCl₅·H₂O with an orthorhombic structure and the Pnma space group was produced. With doping with Sb³⁺, these products exhibit one highly efficient and wide yellow emission band (∼450-850 nm) in their photoluminescence (PL) spectra, which covers almost the entire visible spectral range at room temperature; however, they give two emission bands with long decay lifetimes (microseconds) at low temperature. Temperature-dependent steady-state PL, transient PL spectroscopy, temperature-dependent Raman spectra characterization, and theoretical band structure calculations confirm that the dual-band emission at low temperature originates from the dual vibronic levels of the self-trapped exciton (STE) in the hole-vibration state, whose vibration energy is related to the H₂O-NH₄⁺ connection in the valence band. This result proves that the vibronic state in STE formation involves both electrons and holes in the excited states, the opposite of this happens in the electron-vibration band in most perovskite halides. These results provide new insight into the luminescent mechanism of Sb³⁺ in halide perovskites, especially used for emission color modulation by the temperature-dependent electron- or hole-vibration processes.