Metal nano particles has higher extinction (scattering +absorption) than conventional organic dye molecules, and obviously better than nano semiconductors,
Absorption in metals and semiconductors nanoparticles can be comparable. Semiconductor nanoparticles absorbs photons due excitation of electrons to high energy levels, metal nanoparticles absorbs photons due excitation of plasmon at resonance frequency. Plasmon nanoparticles inappreciable emission because they don't have energy gap. Only very little metal nanoparticles, such as clusters has emission.