  We present an efficient photon-echo experiment based on atomic frequency
combs [Phys. Rev. A 79, 052329 (2009)]. Echoes containing an energy of up to
35% of that of the input pulse are observed in a Pr3+-doped Y2SiO5 crystal.
This material allows for the precise spectral holeburning needed to make a
sharp and highly absorbing comb structure. We compare our results with a simple
theoretical model with satisfactory agreement. Our results show that atomic
frequency combs has the potential for high-efficiency storage of single photons
as required in future long-distance communication based on quantum repeaters.
