Influence of Ag nanoparticles on the luminescence dynamics of Dy ³⁺ ions in glass: The "plasmonic diluent" effect

This work demonstrates that metallic nanoparticles (NPs) embedded in rare-earth (RE) co-doped dielectrics are able to produce an effect analogous to a reduction in the effective concentration of the luminescent RE ions in the matrix, herein coined the "plasmonic diluent" effect. This has been revealed explicitly for Dy³⁺ and Ag NP co-doped aluminophosphate glasses, which were investigated using optical absorption and photoluminescence (PL) spectroscopy with emphasis on the influence of plasmonic NPs on the luminescence decay dynamics of Dy³⁺ ions. The glasses were prepared using the melt-quenching technique, where the precipitation of Ag NPs was subsequently induced by heat treatment (HT). The development of the surface plasmon resonance (SPR) band of Ag NPs at around 410 nm resulted in the quenching of Dy³⁺ emission for the ⁴F_9/2 → ⁶H_15/2, ⁶H_13/2 transitions (484, 574 nm) under resonant excitation of ⁶H_15/2 → ⁴I_15/2 transition at 450 nm. The decay of the ⁴F_9/2 excited state was monitored at 574 nm (away from SPR) under excitation at 450 nm (within SPR), where the PL dynamics indicated the presence of two populations of Dy³⁺ ions in the glasses, in connection with slow (τ_s) and fast (τ_f) lifetime components. A tendency of the decay times to increase gradually with HT holding time was observed as the volume fraction of the plasmonic Ag particles increased. The data are interpreted in terms of an ion-to-particle excitation energy transfer operating via surface plasmons in the nanoscale metal. This produces a Dy³⁺ deactivation effect analogous to a lowering in the effective concentration of emitting Dy³⁺ ions in the matrix, i.e., the metal NPs play a role as a "plasmonic diluent" in the glass system with respect to the luminescent RE ions.