A physical method to develop a scintillator with both a large light output and a quick response is proposed and demonstrated. A direct-gap semiconductor often exhibits ultrafast scintillation components with subnanosecond decay time constants at very low temperatures. However, the exciton luminescence is significantly quenched at room temperature to lose the practical merits. The authors found that the thermal quenching was effectively prevented by constructing a low-dimensional quantum confinement system and a practical amount of light output was obtained at room temperature without losing the quickness of the radiative recombination of the exciton. Crystals of (C6H 13NH3)2PbI4 having a multiple quantum well structure exhibited three decay components of 390 ps, 3.8 ns and 16 ns with the ratios of 28%, 29% and 43%, respectively. The total light output at 300 K was 11% of that of NaI:Tl.