LAUSR

Abstract In this paper we report the synthesis of reduced graphene oxide doped with silver nanoparticles using aqueous extract of Psidium guajava. The dependence of photoluminescence (PL) quenching efficiency of reduced graphene oxide with variable dosage of silver nanoparticles using methylene blue as a model dye is investigated. The effect of excitation energies on the PL quenching efficiency of as-synthesized samples is also systematically studied. At 420 nm excitation, the plasmonic field of silver nanoparticles accelerates charge transfer from methylene blue to reduced graphene oxide resulting in efficient PL quenching as compared to pristine reduced graphene oxide. However at 650 nm excitation, the PL quenching efficiency of reduced graphene oxide surpasses silver nanoparticles doped reduced graphene oxide. This is attributed to strong interaction between reduced graphene oxide and methylene blue in absence of plasmonic fields at lower excitation energies. In order to enhance the quenching efficiency of silver nanoparticle doped reduced graphene oxide at 650 nm excitation, the concentration of silver nanoparticles over graphene surface is increased. This leads to increase in inhomogeneously sized and shaped nanoparticles over graphene surface which not only broadens the plasmonic absorption band but also improves the quenching efficiency at 650 nm. The schematics of charge transfer states via which the PL quenching occurs at different excitation energies are also presented.