The time evolution of the 1.54 µm Er3+ photoluminescence intensity of Er-doped silicon following a 30 µs excitation pulse in investigated. It is found that a 9 K, the 1.54 µm luminescence from Er3+ continues to increase up to 50 µs after the pulse is terminated, when excess photocarriers no longer exist. The provides the first direct experimental evidence that a state in the forbidden gap of silicon acts as the gateway to the excitation of Er3+. Further analysis indicates recombination of bound excitons to be the most likely excitation mechanism.