Bulky Counterions: Enhancing the Two-Photon Excited Fluorescence of Gold Nanoclusters

TL;DR

This paper demonstrates that using bulky counterions and suitable solvents can significantly enhance the two-photon excited fluorescence of gold nanoclusters, achieving a 30-fold increase in signal.

Contribution

It extends the use of bulky counterions from linear fluorescence to nonlinear optical regimes, specifically enhancing two-photon excited fluorescence in gold nanoclusters.

Findings

30-fold increase in TPEF signal at ~600 nm

TPEF cross section estimated between 0.1 to 1 GM

Effective strategy for nonlinear optical enhancement

Abstract

Increasing fluorescence quantum yields of ligand-protected gold nanoclusters has attracted wide research interest. The strategy consisting in using bulky counterions has been found to dramatically enhance the fluorescence. In this communication, we push forward this concept to the nonlinear optical regime. We show that by an appropriate choice of bulky counterions and of solvent, a 30-fold increase in two-photon excited fluorescence (TPEF) signal at ~600 nm for gold nanoclusters can be obtained. This would correspond to a TPEF cross section in the range of 0.1 to 1 GM.