The effects of organic moieties on the luminescence properties of organic−inorganic layered perovskite-type compounds were investigated. Three single crystals were fabricated, namely, (C 4 H 9 NH 3 ) 2 PbBr 4 {C4}, (C 6 H 5 CH 2 NH 3 ) 2 PbBr 4 {Ben}, and (C 6 H 5 C 2 H 4 NH 3 ) 2 PbBr 4 {Phe}. Among the single crystals, the exciton emission of Phe showed the highest quantum efficiencies. The quantum efficiencies of C4 and Ben only were 0.02 and 0.17 times that of Phe, respectively. The radiative and nonradiative decay rates were calculated from the quantum efficiencies and luminescence lifetimes. The relative values of the quantum efficiencies were in accordance with the values of the radiative decay rates. The results indicate that the luminescence properties of the organic−inorganic hybrid compounds may be governed by the excitonic properties of the inorganic layer and not by the concentration of any structural defects. Focusing on the geometry of the inorganic layers, the Pb−Br−Pb bond angles between the adjoining PbBr 6 2− octahedra of each compound were 150°(Ben), 152°(Phe), and 155°(C4). In addition, only Phe showed structural distortion inside the PbBr 6 2− octahedron with Br−Pb−Br bond angles of 171°. The increase in the radiative decay rate can be attributed to the increase in the reduced mass of the excitons from these structural distortions that lead to a decrease in the Bohr radius of the excitons. The results indicate that the luminescence properties of the organic−inorganic hybrid compounds are governed by the structural geometry of the inorganic layer.

We investigated scintillation properties of organic–inorganic layered perovskite-type compounds under gamma-ray and X-ray irradiation. A crystal of the hybrid compounds with phenethyl amine (17 × 23 × 4 mm) was successfully fabricated by the poor-solvent diffusion method. The bulk sample showed superior scintillation properties with notably high light yield (14,000 photons per MeV) under gamma-rays and very fast decay time (11 ns). The light yield was about 1.4 time higher than that of common inorganic material (GSO:Ce) confirmed under 137Cs and 57Co gamma-rays. In fact, the scintillation light yield was the highest among the organic–inorganic hybrid scintillators. Moreover, it is suggested that the light yield of the crystal was proportional with the gamma-ray energy across 122–662 keV. In addition, the scintillation from the crystal had a lifetime of 11 ns which was much faster than that of GSO:Ce (48 ns) under X-ray irradiation. These results suggest that organic–inorganic layered perovskite-type compounds are promising scintillator for gamma-ray detection.

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The photoluminescence and scintillation properties of Cs2HfCl6 and Cs2ZrCl6 crystals were investigated. Two emission bands in the photoluminescence spectra were observed at 375 and 435 nm for the Cs2HfCl6 crystal and at 440 and 479 nm for the Cs2ZrCl6 crystal. Similar spectra were observed for radioluminescence. The decay time constants were found to be about 2.2 and 8.4 µs for Cs2HfCl6 and 1.5 and 7.5 µs for Cs2ZrCl6. The scintillation light yields were estimated to be 27,500 and 25,100 photons/MeV for Cs2HfCl6 and Cs2ZrCl6, respectively.

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