We synthesized (C6H5C2H4NH3)2Pb1−x Ni x Br4 single crystals with different concentrations of Ni (x = 0.05, 0.1, 0.25, and 0.5) by the poor-solvent diffusion method and evaluated their photoluminescence (PL) and scintillation properties. In the PL contour maps, exciton luminescence peaks appeared at 410 and 440 nm for all the samples. The obtained PL quantum yields of the x = 0.05, 0.1, 0.25, and 0.5 samples were 25.1, 31.8, 31.2, and 25.7% within ±2% errors, respectively, In the scintillation spectra, excitonic luminescence peak was observed at 440 nm for all the samples. The scintillation light yields of the x = 0.05, 0.1, 0.25, and 0.5 samples were estimated to be ∼16 000, ∼17 000, ∼16 000, and ∼15 000 photons MeV−1 within ±10% errors, respectively. When we investigated the correlations between the γ-ray energies and the corresponding photoabsorption peak channels, all the samples had a good linearity over a range of 22–662 keV.