Two-Dimensional Lead-Free Hybrid Nickel-Based Perovskites with Two-Color Emission and Their Scintillation Properties

Recently, two-dimensional (2D) organic−inorganic perovskites have attracted significant attention due to their unique optoelectronic properties, including a tunable bandgap and high photoluminescence quantum efficiency. However, many 2D perovskites remain underexplored and may prove to be excellent candidates for device fabrication. Hence, we investigate a family of Pb-free, Ni-based 2D perovskites with the general formula (A) 2 NiCl 4, where the organic cation A is varied among phenylmethylammonium (PMA), phenylethylammonium (PEA), and phenylpropylammonium (PPA). Photoacoustic spectroscopy and photoluminescence measurements reveal two distinct optical features: a 300 nm ligand-surface-related band and a 500 nm band assigned to Ni d -states, which is the bandgap in these crystals. Furthermore, radioluminescence experiments demonstrate a high light yield for (PPA) 2 NiCl 4, reaching 23,000 photons/MeV at 80 K, highlighting its potential as a promising low-temperature scintillator.