Fig. 1. In situ emission measurements of (bmpy)₆[Pb₃Br₁₂] under high pressure. (a) PL spectra at selected pressures. The insets show the pressure-induced emission at 1.6 GPa and the robust emission at 80 GPa. The small kinks at around 2.25 eV are caused by the dichroic beam splitter (FF376-Di01, Semrock) in our measurement system. (b) Integrated PL intensity as a function of pressure. (c) Fluorescent images at selected pressures.

Fig. 2. Bandgap evolution of (bmpy)₆[Pb₃Br₁₂] under high pressure. (a) UV-vis absorption spectra at high pressures. (b) Bandgap as a function of pressure. The insets show optical micrographs at selected pressures. (c) Bandgap evolution of (bmpy)₆[Pb₃Br₁₂] compared with other hybrid metal halides, where the data are collected from the literature.^29–36

Fig. 3. In situ structural characterizations of (bmpy)₆[Pb₃Br₁₂] under high pressure. (a) Schematic crystal structure of (bmpy)₆[Pb₃Br₁₂] along different crystallographic axes and the [Pb₃Br₁₂]⁶⁻ trimer cluster. (b) XRD patterns at selected pressures. (c) Lattice constants and a/c ratio as a function of pressure. (d) Evolution of unit-cell volumes.

Fig. 4. (a) PL emerging and quenching pressures of (bmpy)₆[Pb₃Br₁₂] in comparison with those of other 0D and 1D metal halides. (b) Stokes shift and phonon energy as functions of pressure. (c) Schematic of pressure-induced emission from excitons. GS and ES indicate the ground state and excited state, respectively.

Table 1. Summary of PL emerging and quenching pressures for various metal halides.