A metal nanoparticle system has been prepared by 200 KevAg+ion implantation into perfect single crystalSiO2at room temperature to dose:6.7×1016/cm2.The system presents quasidual-layer structure: the shallower implanted layer containing noninteracting small Ag nanoparticles and the deeper layer containing interacting large nanoparticles, in which great red shift, about 1 eV, comparing with the plasmon resonance frequency of the noninteracting nanoparticle, can be clearly observed. The red shift is attributed to the multipoles interaction among the high density nanoparticles at external electric field. Moreover, the magnitude of red shift increases with implanted dose. ©1998 American Institute of Physics.