Silver NPs oxidize easily on the surface. Even though the plasmonic properties are influenced, it can be still used for any plasmonic application.
For more info see https://www.researchgate.net/publication/235949878_Influence_of_surface_oxidation_on_plasmon_resonance_in_monolayer_of_gold_and_silver_nanoparticles_Influence_of_surface_oxidation_on_plasmon_resonance_in_monolayer_of_gold_and_silver_nanoparticles?ev=prf_pub
Data Influence of surface oxidation on plasmon resonance in monol...