Mechanistic insights into silver-doped gold clusters for advanced photonic and nonlinear optical response

Nonlinear optical (NLO) materials are crucial for the advancement of optoelectronic and photonic technologies because of their capacity to modify light-matter interactions. This paper conducts a thorough density functional theory analysis of the structural, electrical, and nonlinear optical characteristics of both pure and silver-doped gold (Au) clusters. This is the first theoretical investigation of the NLO behavior of this category of Ag-doped Au clusters. Our findings demonstrate that the addition of silver substantially reduces the HOMO-LUMO energy gap, decreasing from 5.65 eV in pure clusters to as low as 2.28 eV, signifying increased electronic polarizability and higher nonlinear optical sensitivity. To clarify the source of this augmentation, we conducted comprehensive investigations of the density of states, frontier molecular orbitals, molecular electrostatic potential, electron density difference, and non-covalent interaction analysis. This indicates significant charge redistribution, enhanced dipole moments, and the emergence of metallic bonding properties after silver doping. The dynamic NLO coefficients are calculated at the usual Nd:YAG laser wavelength of 1064 nm (ω = 0.0428 au). Notably, the first-order hyperpolarizability β _(-ω;ω,0) reached 1.65 × 10³ au. for Au₁Ag₄, while the frequency-dependent first hyperpolarizability β _(-2ω;ω,ω) peaked at 4.33 × 10⁴ au for Au₃Ag₂. Furthermore, the second hyperpolarizability γ _{(-2ω;ω,ω,0)} attained a remarkable value of 1.68 × 10⁷ au. These findings highlight the exceptional NLO performance of Ag-doped Au clusters and underscore their potential as promising candidates for next-generation photonic and optoelectronic device applications.