Efficient no-phonon (NP) luminescence was observed from a pair of pure-Ge/pure-Si on relaxed Si0.82Ge0.18 which separately confines electrons and holes in neighboring quantum wells. Anomalous broadening of the photoluminescence linewidth from the wetting layer occurred at around critical Ge coverage of Ge island formation, indicating that the microscopic interface roughness becomes significant at the initial stage of the island formation. At around the critical coverage, the enhanced NP feature was clearly observed at 77 K owing to the realization of rigorous confinement potential for exciton localization.