We find that in SiGe clusters grown on Si using the Stranski-Krastanov (S-K) growth mode, (i) photoluminescence (PL) spectra, (ii) PL lifetime and (iii) PL thermal quench activation energies all exhibit a strong dependence on the excitation intensity. Under PL excitation intensity increasing from 1 to 104 W/cm2, the PL spectra exhibit a blue shift from below the Ge bandgap up to ∼970 meV. The PL lifetime shows a strong dependence on the detection wavelength, decreasing from 20 us at ∼0.8 eV to 200 ns at ∼ 0.9 eV. The process of PL thermal quenching has two clearly distinguished activation energies. At low temperature, a small (∼15 meV) and excitation-independent activation energy is attributed to exciton thermal dissociation. At higher temperature, an excitation-dependent PL thermal quenching activation energy (increasing from ∼ 120 to 340 meV as the excitation intensity increases) is found, and it is attributed to hole redistribution via tunneling and/or thermal ionization over the Si/SiGe valence band energy barrier.