Microstructure and light-induced observable-light emission of porous Si are studied by the use of scanning electronic microscope,atomic force microscope,and photoluminescent Spcetrums.It is shown that there is a close relation between mechanism of light emission and microstructure of porous Si.The results obtained in this paper agree with those predicted by the model in which porous Si consists of much amount of cylindric or ballic crystal structures,and exhibits a kind of ordering structure,efficient emmission of light of porous Si originates from some nanostructures-quantum wires and quantum...