Tuning photoluminescence properties of Au clusters by surface modification and doping: lessons from case studies of icosahedral Au

The photoluminescence (PL) properties of monolayer-protected gold nanoclusters (Au MPCs) have been extensively studied due to their wide range of potential applications, such as photocatalysis, photosensitization, bioimaging, and tumor therapy. The key factor that determines the PL properties of Au MPCs is the Au core size, but other parameters such as surface modifications and doping also significantly affect the PL properties. To understand and highlight the importance of these secondary parameters on the PL properties, this review article focuses on the ubiquitous icosahedral Au 13 core as a benchmark and addresses the question of how the PL properties are affected by surface modification with X-type (thiolates, alkynyls) and L-type (phosphines, N-heterocyclic carbenes) ligands and doping with heterometals (Ru, Rh, Ir, Ni, Pd, Pt, Ag, Cd). The PL emission energy of Au 13 MPC can be varied in the wide range of 1.1-2.1 eV and PL quantum yields up to 70% can be achieved by appropriate surface modification and doping. Based on the publications available until June 2024, the following empirical rules are derived to tune the PL emission energy and increase the PL quantum yield: (1) The PL emission energy and PL quantum yield can be increased by using L-type ligands and/or doping with small group elements such as Ir, Pt, Ru, and Rh. (2) The PL quantum yield can be enhanced by maximizing the interaction between the ligands through π π or C-H π interaction, chemical bonding, and steric packing. The first rule follows the energy gap law and can be understood qualitatively by simple schemes based on the jellium model. The last rule is due to the suppression of non-radiative decay by the stiffening of the Au core. We hope that this review will help the audience to establish rational guidelines for designed PL properties. This review article focuses on the ubiquitous icosahedral Au 13 core protected by organic ligands as a benchmark and derives empirical rules for tuning and enhancing photoluminescence properties through surface modification and heterometal doping.