Silica based luminescent nanoparticles provide tremendous potential as biocompatible and robust inorganic materials in nanobiotechnology and nanomedicine. Sol-gel derived silica act as excellent host for covalently encapsulating organic fluorophores to enhance brightness while independently controlling the size of the nanoparticle. The first part of this dissertation describes the development of bright multicolor fluorescent silica probes in a layer by layer approach. Three spectrally distinct dyes (green, blue and red) were incorporated in three different levels or number of dyes per particle (0, 5, 20) to generate twenty-six spectrally distinguishable nanoparticles. Each particle was designed by precisely controlling the number of dyes per particles and each dye layer was spatially separated by blank silica shell to minimize energy transfer. These particles were used to demonstrate fluorescence multiplexing via cellular uptake. The second part of this thesis describes development of chemiluminescence based probes. Template based near-infrared dye was covalently incorporated into mesoporous silica nanoparticles seems to orient the dye such that the non-radiative pathway disappears resulting in brightness enhancement for chemiluminescence. These highly porous nanoparticles facilitated the diffusion of the reactive precursor resulting in chemiluminescence. These particles along with polybase additives were used to tune the kinetics of photon emission.