We show that the fast blue (maximum at about 3.0-3.2 eV) photoluminescence from spark processed silicon originates from tungsten doping when the sample is processed with a tungsten counter-electrode. A similar effect is found also for molybdenum and chromium. If a silicon tip is used as counter-electrode, the photoluminescence is about a factor of 30 weaker and red shifted with a maximum at about 2.2-2.3 eV, Because of the limited sensitivity of the RES technique used, transition metal impurities, such as Zn, are suspected but cannot be definitively proven as the radiative centers in this case.