ZnO nanoparticles are recently attracting a lot of interest due to their novel optical, electrical, mechanical, and chemical properties, due to surface and quantum confinement effects. A stable dispersion of ZnO nanoparticles with a uniform particle diameter of 5 nm has been synthesized via chemical precipitation. The surface of the particles has been functionalized with dodecanethiol for enhanced compatibility and dispersion in polymethylmethacrylate (PMMA). Transparent luminescent nanocomposite powders were obtained using solution mixing and solvent casting of ZnO nanoparticles in PMMA. This powder was used to produce injection-molded luminescent nanocomposites plaques. The effect of the ZnO nanoparticles on the polymer structure has been investigated by employing thermomechanical and dielectric spectroscopy analyses.