Plasmon-controlled, ultra-bright, excitation-polarization-independent photoluminescence from individual Ag nanoplates

Fanwei Zhang,Lijun Wu,Lizhen Yang,Hongjin Hu,Qiang Li,Jiepeng Wu,Tao Li

doi:10.1515/nanoph-2019-0555

Abstract

Abstract Fluorescent metallic nanoparticles with high quantum yield are highly desirable for optical imaging in the fields of biology and materials science. We investigate the photoluminescence (PL) properties of Ag nanoplates, particularly triangular ones, systematically at the single-particle level under different excitation conditions. We find that their emission is controlled by surface plasmon resonances (SPRs). Because of their high geometric symmetry, the shape and intensity of the PL spectrum from Ag triangular nanoplates are independent of the excitation polarization. Under excitation wavelengths of 473, 532 and 633 nm, the PL quantum yield (QY) of Ag triangular nanoplates is found to be twice that of Au nanorods at similar SPR wavelengths. It can be attributed to the stronger and broader SPR response, which can make the PL more intense not only in the spatial domain but also over a larger range in the frequency domain. Our investigations will extend the application of Ag nanoplates in imaging, labeling, and emitting, especially at the single-molecule level, due to their ultra-bright, stable, and polarization-independent PL. This method to enhance the PL signal, in both the spatial and frequency domains, can be easily expanded to other systems.

Highlights

Owing to their unique properties induced by the excitation of localized surface plasmon resonances (SPRs) [1, 2], noble metal nanoparticles (NPs) have attracted much attention in the fields of sensing [3], photovoltaics [4], catalysis [5], and surface-enhanced Raman spectroscopy (SERS) [6], to name but a few
With the change of the excitation polarization, the PL spectrum remains constant, which originates from the high degree (≥3-fold) of the geometric symmetry of the NPs
Under 473, 532, and 633 nm linearly polarized excitations, we found that the PL quantum yield (QY) of Ag triangular nanoplates (TNPs) was about twice as high as that of Au nanorods (Au NRs) with same effective sizes at similar SPR wavelengths

Summary

Introduction

Owing to their unique properties induced by the excitation of localized surface plasmon resonances (SPRs) [1, 2], noble metal nanoparticles (NPs) have attracted much attention in the fields of sensing [3], photovoltaics [4], catalysis [5], and surface-enhanced Raman spectroscopy (SERS) [6], to name but a few. Triangular Ag nanoplates are interesting since they can generate more hot spots and huge electric field enhancement around the tips and edges due to their special symmetric characteristics [27] Their unique optical properties can be tuned by controlling the aspect ratio. Based on the calculated field intensity over the volume surrounding individual Ag TNPs and Au NRs within the whole SPR spectrum range, the high QY of Ag TNPs can be attributed to their stronger and wider SPR response compared to Au NRs. The ultrabright, stable, and excitation-polarization-independent PL from Ag nanoplates means that they are promising candidates for applications in labeling, imaging, and emitting at the single-nanoparticle level, at which their special properties will greatly relax the constraints for wavelength and excitation-polarization alignments. Our investigations will be helpful to understand the PL and PL enhancement mechanisms of Ag NPs and other noble metal NPs more comprehensively

Experimental section

Results and discussion

Conclusion