Time-resolved photoluminescence study of tris(8-hydroxyquinolinato) aluminium with surface plasmon resonance of Ag nanoparticles

Surface plasmon resonance (SPR) of Ag nanoparticles (NPs), and its emission enhancement properties are investigated by time-resolved photoluminescence spectroscopy using tris(8-hydroxyquinolinato)aluminium (Alq₃), which is generally applied in organic light-emitting diode, as the emitter. 5-nm-thick Ag island-films were fabricated, and annealed at various temperatures to vary the size of the Ag NPs. The peak position of the SPR band in the absorption spectra of Ag NPs blue-shifts with increasing annealing temperature, that is, the SPR frequency is controlled by the NP size. Comparison of the photoluminescence (PL) spectra of Alq₃ with and without Ag NPs annealed at 150 °C indicates 1.2-fold enhancement of PL for Alq₃ with Ag NPs compared to the reference Alq₃. From the temperature dependence of the PL intensity and lifetime of Alq₃ with Ag NPs, we evaluated the degree of enhancement of the radiative recombination rate in the presence of the localized surface plasmon of Ag NPs, in comparison with the competitive non-radiative quenching process.