Pressure response of decylammonium-containing 2D iodide perovskites

Manipulation by external pressure of the optical response of 2D Metal Halide Perovskites (MHPs) is a fascinating route to tune their properties and promote the emergence of novel features. We investigate here DA2PbI4 and DA2GeI4 (DA = decylammonium) perovskites in the pressure range up to ~12 GPa by X-ray powder diffraction, absorption, and photoluminescence spectroscopy. Although the two systems share a similar structural evolution with pressure, the optical properties are rather different and influenced by Pb or Ge. DA2PbI4 shows a progressive red shift from 2.28 eV (P = 0 GPa) to 1.64 eV at 11.5 GPa, with a narrow PL emission, whereas DA2GeI4, changes from a non-PL system at ambient pressure to a clear broadband emitter centered around 730 nm with an intensity maximum at about 3.7 GPa. These results unveil the role of the central atom on the nature of emission under pressure in 2D MHPs containing a long alkyl chain.