The electro-optic properties of highly structured polymer–liquid-crystal composites based on acrylate monomers and E7 liquid crystals doped with ${{\rm Y}_2}{{\rm O}_3}$Y2O3 nanoparticles are considered. The influence of nanoparticles on the diffraction efficiency, the driving voltage, the dielectric properties, and the dynamics of the formation of holographic and polarization holographic diffraction gratings inscribed in polymer–liquid-crystal composites is demonstrated. The diffraction efficiency of the doped holographic diffraction gratings decreases, and that of the polarization diffraction gratings increases. Doping with nanoparticles leads to a decrease in driving stresses and increases the formation time and dielectric constant of highly structured polymer–liquid-crystal composites.