Arrays of 40 - 50 nm quantum dots were fabricated from Si- Si1-xGex single quantum well and superlattice structures grown by molecular beam epitaxy. The dots showing strong luminescence were studied by synchrotron source x-ray diffraction. Some of the dots were coated with SiNx films containing different build-in stresses. It was found that the luminescence intensity depends strongly on the amount of stress in the SiNx coating, being strongest when the stress was close to zero. A strain symmetrization process occurred in the bright dots. Although an exact physical origin is not yet available, it is exciting that these quantum dot diodes work at room temperature and that the whole fabrication procedure is compatible with Si- technology.