Scientists are constantly searching for new processing techniques which are capable of modifying the properties of materials. This could yield alternative characteristics that may lead eventually to new consumer products or, more importantly, provide a better understanding of nature. Such a new technique is spark-processing, which has been shown to change remarkably the optical properties of silicon (and other materials). Specifically, spark processing (sp) creates a substance which transforms Si into a strongly photo-luminescing and cathodoluminescing material (in contrast to ordinary Si which is not light emitting). The resulting material is extremely stable against high temperature annealings, HF etching, and laser irradiation. The emission wavelengths range from violet to green to red, depending on the processing parameters. Further, sp-Si is ferromagnetic (compared to conventional Si which is diamagnetic). A new photoresitive device has been created from sp-Si which, upon impingement of light, increases or decreases its resistivity depending on geometric variables. Sp-Si is produced by high frequency, high voltage, low current electric pulses which are applied for a short time between a Si substrate and a counter electrode.