We investigate the heavy atom effect on difluoroboron(iii) β-diketonate (BF2bdk) luminescent compounds. The iodine-substituted BF2bdk powders with 38 wt% iodine substituents show insignificant afterglow at 77 K. Unexpectedly, when doped into phenyl benzoate matrices, the iodine-substituted BF2bdk exhibits bright room-temperature phosphorescence with lifetimes of up to 1.0 s under ambient conditions.