Both nanocrystalline and nanoporous silicon shows interesting optical and light emissionrnproperties. As the system size goes to nanoscale the optical band gap, radiative transitions,rnoscillator strength, absorption coefficient and dielectric function increases. The nanosiliconrnshows unusual optical properties which have tremendous importance for nanophotonics andrnoptoelectronic applications. The purpose of the thesis is to study the light emission and opticalrnbehavior of nanoporous silicon cluster (quantum dot) with varying porosity and oxygen as wellrnas hydrogen at the surface. We examine these properties combining k.p perturbation method andrnsurface state model. In order to clarify the morphological effects such as size, surface passivationrnand porosity level of a nanoporous silicon cluster on its optical properties, calculation of opticalrnabsorption coefficient, dielectric function and oscillator strength of porous silicon nanoclusters asrna function of size (diameter) through energy gap is discussed using k.p method. The effects ofrnnanoparticles size along with surface passivation and porosity level on optical band gap havernalso been investigated and compared with experiment. The porosity and surface effects arernincorporated through some empirical parameters c and Î± in our model. Furthermore, we examinernthe main factors that causes photoluminescence peak to shift towards left or to the smallerrnwavelength of visible spectrum (blue shifted). Our results are in conformity with some otherrnexperimental and theoretical findings. We also present some of the important applications ofrnsilicon nanostructures and provide a control mechanism for light emission through ourrninvestigation