  We study the time behavior of entanglement between two noninteracting qubits
each immersed in its own environment for two different non-Markovian
conditions: a high-$Q$ cavity slightly off-resonant with the qubit transition
frequency and a nonperfect photonic band-gap, respectively. We find that
revivals and retardation of entanglement loss may occur by adjusting the
cavity-qubit detuning, in the first case, while partial entanglement trapping
occurs in non-ideal photonic-band gap.
