A bulk sample of an organic–inorganic (OI) perovskite crystal of (C 6 H 5 C 2 H 4 NH 3 ) 2 PbBr 4 with a layered structure showing excellent luminescent properties was rapidly synthesised. The raw materials of OI crystal were impregnated into nanoporous glass having 4-nm pores and dried, obtaining a translucent sample of OI nanocrystals in glass (OIiG). An absorbance shoulder was observed at E = 3.04 eV for OIiG, which was attributed to exciton bands, and photoluminescence (PL) duration times of τ 1 = 2.8 ns and τ 2 = 8.6 ns were recorded for OIiG. In contrast, for a single-crystal sample, E = 2.94 eV, τ 1 = 4.1 ns, τ 2 = 11.0 ns. Compared to those of the single-crystal sample, the OIiG has a higher absorbance energy, and the duration time was shorter. The exciton activation energy was 195 meV for OIiG, in contrast with 121 meV for single crystal. We propose that these changes are due to the size effect because the particle size (3–4 nm in diameter) in the OIiG is close to the Bohr radius of layer-structured OI crystals.