Optical coherent transients are reported here for the first time in a pure, optically concentrated material (EuP5O14). Qualitatively new behavior is found in the form of a systematic variation of the homogeneous dephasing time T2 (20 sec) across the inhomogenously broadened line. This is interpreted as evidence for delocalization of the excitation. In contrast, the dilute impurity system Eu3+: YAlO3 shows narrower lines and no frequency dependence of T2. © 1980 The American Physical Society.