We show that both the morphology and the optoelectronic properties of SiGeislands growing in the pits of periodically pre-patterned Si(001) substrates aredetermined by the amount of Ge deposited per unit cell of the pattern. Pit-periods (p) ranging from 300 to 900 nm were investigated, and Ge growth wasperformed by molecular beam epitaxy (MBE) at temperatures of 690 and760 °C. The ordered SiGe islands show photoluminescence (PL) emission, whichbecomes almost completely quenched, once a critical island volume is exceeded.By atomic force and transmission electron microscope images we identifythe transition from pyramid-shaped to dome-shaped islands with increasingp. Eventually, the nucleation of dislocations in the islands leads to PL quenching. Below acritical Ge coverage a narrowing and a blue shift of the PL emission is observed,as compared to islands grown on a planar reference area of the same sample.