We have studied the luminescence properties of chemically synthesized Si8 clusters and Si-based polymers with different backbone structures. The optical properties of Si8 clusters depend strongly on the shape of clusters. The luminescence properties of the cubic Si8 cluster are different from those of the chain and ladder Si8 clusters. Moreover, the ladder and network Si polymers whose backbones are constructed by the organosilicon units with three Si-Si bonds exhibit broad photoluminescence spectra in the visible region. These luminescence properties are entirely different from those of the chain structure constructed by the organosilicon units having two Si-Si bonds. The unique optical properties of silicon clusters and polymers are discussed.