Three-dimensional SiGe nanostructures grown on Si using molecular beam epitaxy exhibit photoluminescence (PL) in the important spectral range of 1.3-1.6 μm. At a higher level of photo-excitation, thermal quenching of the PL intensity is suppressed and the previously accepted type II energy band alignment at Si/SiGe cluster hetero-interfaces no longer controls radiative carrier recombination. Instead, a dynamic type I energy band alignment governs the strong decrease in carrier radiative lifetime and further increase in the luminescence quantum efficiency. In contrast to the strongly temperature dependent and slow radiative carrier recombination found in bulk Si, Auger mediated PL emanating from the nanometer-thick Si layers is found to be nearly temperature independent with a radiative lifetime approaching 10-8 s, which is comparable to that found in direct band gap III-V semiconductors. Such nanostructures are thus potentially useful as CMOS compatible light emitters and in optical interconnects.