Origin of luminescence properties and synthetic methods for gold- and bimetallic gold-based nanomaterials

Abstract

Organic emissive dyes, which were first synthesized in the mid-19th century, have played a major role in the field of sensing and biological imaging for several decades. The extensive use of π conjugation in organic dyes has shown their red-shifted emission from the ultraviolet (UV) to near infrared (NIR) region. The emission property modulation is not only restricted to π conjugation, but also affects the rotation of their bonds, functional group modification and intermolecular interactions. The photobleaching property of organic dyes makes it necessary to develop alternative emissive molecules and materials. Among the alternative emissive sources, gold-based nanomaterials showed 10⁻⁴ to 10⁻⁵ quantum efficiency for the first time in 1998. The quantum yields of these systems are mostly low except for a few exceptional cases in comparison to organic dyes. However, the high extinction coefficient values of these gold-based nanomaterials overcome the issue of overall brightness. The high stability of gold-based nanomaterials has gained attention in sensing and biological applications. The origin of the emission in these gold-based nanomaterials varies significantly among bimetallic nanoclusters (BMNCs) and metal oxide nanoparticles (NPs). In this review article, we deliberate on the foundation of luminescence properties among gold-based nanomaterials and compare their synthetic methods in detail.