Silicon (Si\label{Si}) is a material of paramount importance in both microelectronics and photonics.  The semiconducting properties of silicon are behind the fundamental concepts of  most of the electronic devices as diodes and transistors. The concept of integration has allowed processing very small devices, reaching the nano metric size. The high refractive index of silicon allows confining light in structures whose size  is in the micrometric range. This is the case of photonic devices such as waveguides and cavities. Normally both electronic and photonic devices are based on planar technology, i.e.: they have a flat topology, being this a source of losses. It is well known that spherical cavities confine light much stronger than planar cavities. This PhD thesis reports on the development of a new type of spherical microparticles we call as Silicon Colloids. Because of their spherical shape, high refractive index and smooth surface, they work as optical microcavities with well defined resonating modes in the near infrared range. This thesis will report on the synthesis, structural and optical properties of silicon colloids with diameter from 0.5 to 3.5 mu. Silicon colloids may facilitate development of high quality factor optical microcavities with strong light confinement effects, allowing integration of electronic and photonic devices such as a p-n junction into a single colloidal particle. This thesis will report also on silicon colloids as building blocks of Photonic Sponges formed by disordered networks of silicon microspheres of different sizes that scatter light strongly in a wide range of wavelengths.