Ion beam mixing of silver-covered oxide films by 400 keV argon ions induces the formation of silver nanoparticles on the oxide surface. Using consecutive conformal dielectric deposition and ion beam mixing, multiple layers of the nanoparticles can be fabricated. By means of diffusive reflection and absorption spectroscopy, surface plasmon resonances of silver nanoparicles are investigated in SiO2, Al2O3 and TiO2 films containing single and double layers of the Ag nanoparticles. We show that, compared to the extinction spectra, the diffusive reflection spectra allow clear observation of the excited plasmon modes and their modifications due to the dielectric environment and the interaction between the particles.