- Electronic structure and magnetic properties for Mn-, Fe-, Co-, and C-doped cerium dioxide (AxCe1-xO2, A=Mn, Fe, Co, C) with homogeneously oxygen vacancies have been investigated by means of the first principle calculations based on local density approximation (LDA) and LDA+U scheme, packaged in the ABINIT code. The calculation was performed using self-consistent pseudo-potential plane wave and projected augmented plane wave (PAW). The results indicate that CeO2 has energy band-gap about 2.72 eV and the transition doped and oxygen vacancies seem to be crucial for the appearance of a ferromagnetic. Furthermore, the band structure of Si(1-x-y)GexSny grown on CeO2 substrate (Si(1-x-y)GexSny/CeO2) with x and y varying in the range 0 to 0.4 was calculated by empirical-pseudopotential method. It shows possibility of achieving of direct band-gab semiconductor (0 to 0.8 eV) by using appropriate silicon germanium and tin composition. Therefore, the (Si(1-x-y)GexSny/CeO2) alloy can be useful for a number of optoelectronic applications, such as laser and solar cell, and spintronic applications.