We report the synthesis and characterization of transparent nanocomposites consisting of YVO₄ : Eu nanoparticles in polymer matrices. The composite materials are made by in situ polymerization of particle dispersions in methyl methacrylate (MMA) and lauryl acrylate (LA). Two different pathways for the preparation of these dispersions and their polymerization are presented. The first method, based on reverse microemulsions, yields a dispersion of YVO₄ : Eu nanoparticles in MMA. The microemulsion droplets function as space-confined containers for the precipitation reaction of YVO₄ : Eu and their hydrodynamic diameter can be controlled in the range of 6-90 nm as measured by dynamic light scattering (DLS). When a microemulsion with a droplet size of 7 nm is used, nanoparticles with a crystallite size of 5.8 nm are obtained as determined from X-ray diffraction patterns. Crystalline particles are identified by transmission electron microscopy (TEM) in samples taken directly from the microemulsion. A phase transfer of YVO₄ : Eu nanoparticles from an aqueous dispersion into nonpolar solvents is the key step for the second preparation method. A crystallite diameter of 5 nm was determined by XRD, while crystalline particles in the size range of 3-18 nm could be identified with TEM. The modified particles were dispersed in LA to give a clear dispersion. No aggregation or particle growth takes place during the steps of phase transfer, isolation and redispersion of the nanoparticles as confirmed by DLS and powder X-ray diffraction. Both particle dispersions in MMA and in LA were polymerized using an in situ polymerization approach resulting in solid nanocomposites with excellent optical properties. The obtained materials are highly transparent (transmission >90% at 600 nm), possess a low haze (0.7-1.4%) and show red photoluminescence upon UV excitation, due to the integration of luminescent YVO₄ : Eu nanoparticles.