We investigated mixed-crystal effects on the luminescence and scintillation properties of organic-inorganic layered perovskite-type compounds. The luminescence and scintillation decay accelerated as the iodine content increased. The radiative and non-radiative decay rates under both ultraviolet and X-ray radiation were calculated; quantum efficiency was used under ultraviolet radiation. The radiative decay rate was almost constant with increasing iodine content under both types of radiation; however, the non-radiative decay rate increased with increasing iodine content. These results indicate that the mixed-crystal effects on the luminescence and scintillation properties are governed by non-radiative processes. Besides, the scintillation decay time was longer than the luminescence decay time although the rise times for both profiles were similar, suggesting that the energy transfer from the organic to the inorganic layer had no effect on the scintillation properties. Moreover, these time profiles became similar with increasing iodine content in the inorganic layer. These results suggest that the difference between the two types of decay can be associated with the scintillation process in the inorganic layer.