||Light from porous silicon (Si) has been an intensive research topic since the report by Canham in 1990. Recently, visible photo-luminescence (PL) has also been reported from porous Si layers formed from polycrystalline Si (poly-Si). The new luminescent porous poly-Si (PPS) film can be formed on Si or non-Si substrates, hence bring numerous novel applications in future Si-based opto-electronic devices. As poly-Si films with various crystallinity and grain sizes can be prepared, study of PPS films can also help to understand and control the mechanisms for light emission from Si. However, due to the difficulty in sample preparation and characterization, there are so far very few reports on luminescent PPS films. In this thesis, we present our systematic study and new results obtained on this important material. PPS submicron thin films have been prepared from anodized and stain-etched LPCVD poly-Si films deposited on Si, oxide and nitride surfaces and doped with post-CVD phosphorus diffusion. The films have been studied by high resolution scanning and transmission electron microscopy, atomic force microscopy, x-ray diffraction and photoluminescence spectroscopy, and Raman studies. New PPS nanostructures and formation mechanisms have been found. A coral-ball formation analogy model is proposed to describe the etching process of porous Si and the formation of PPS films. PPS films are found to have orange-red PL and the PL spectrum is highly comparable to that of porous Si formed from crystalline Si. Intensity of PL is closely related to the anodization and stain etching conditions, crystallinity, and atomic composition of PPS films. A new PL emission model is proposed to relate the PL of PPS films to the presence of carbon and oxygen-rich amorphous Si material, Si nano-crystals in <200> orientation, and oxide in the PPS layers. Fabrication of PPS devices have also been attempted and encouraging results on luminescent PPS micron-size patterns, gas and photo-sensors are also presented and discussed.