Spectral Selectivity of Plasmonic Interactions between Individual Up-Converting Nanocrystals and Spherical Gold Nanoparticles.

Dawid Piątkowski,Magdalena Twardowska,Mikołaj K Schmidt,Javier Aizpurua,Marcin Nyk,Sebastian Maćkowski

doi:10.3390/ma10080905

Abstract

We experimentally demonstrate strong spectral selectivity of plasmonic interaction that occurs between α-NaYF4:Er3+/Yb3+ nanocrystals, which feature two emission bands, and spherical gold nanoparticles, with plasmon frequency resonant with one of the emission bands. Spatially–resolved luminescence intensity maps acquired for individual nanocrystals, together with microsecond luminescence lifetime images, show two qualitatively different effects that result from the coupling between plasmon excitations in metallic nanoparticles and emitting states of the nanocrystals. On the one hand, we observe nanocrystals, whose emission intensity is strongly enhanced for both resonant and non-resonant bands with respect to the plasmon resonance. Importantly, this increase is accompanied with shortening of luminescence decays times. In contrast, a significant number of nanocrystals exhibits almost complete quenching of the emission resonant with the plasmon resonance of gold nanoparticles. Theoretical analysis indicates that such an effect can occur for emitters placed at distances of about 5 nm from gold nanoparticles. While under these conditions, both transitions experience significant increases of the radiative emission rates due to the Purcell effect, the non-radiative energy transfer between resonant bands results in strong quenching, which in that situation nullifies the enhancement.

Highlights

An emitter localized close to a metallic nanoparticle can experience modification of its absorption, emission and non-radiative transition rates
Non-radiative energy transfer between the emitter and metallic nanoparticle starts to dominate, which leads to strong quenching of the emission
In this paper we investigate the optical properties of a hybrid structure composed of spherical gold nanoparticles and nanocrystals with bimodal emission: one emission band centered at 540 nm which is resonant with the plasmon resonance of gold nanoparticles, and another emission band centered at 650 nm which is strongly red-shifted with respect to the plasmon resonance

Summary

Introduction

An emitter localized close to a metallic nanoparticle can experience modification of its absorption (γabs ), emission (γr ) and non-radiative (γnr ) transition rates. Non-radiative energy transfer between the emitter and metallic nanoparticle starts to dominate, which leads to strong quenching of the emission. In such geometries, the spectral properties of the gold tip cannot be tuned in order to ensure optimal spectral matching with absorption or emission bands of the studied emitters. Previous investigations demonstrated a general rule that the largest values of the luminescence enhancement factors are typically observed in configurations where emission is spectrally red-shifted with respect to the plasmon resonance, i.e., where the absorption of the metallic nanoparticle is significantly smaller [14]. The green emission, shows strong decrease of the luminescence intensity due to nonradiative energy transfer to the nearby metallic nanoparticles

Materials and Methods

Results

Photoluminescence

Findings

Conclusions