Modulation of Third-Order Nonlinear Optical Response in Copper-Induced Gold Nanoclusters.

Nonlinear optical (NLO) materials play a pivotal role in controlling laser characteristics, including phase and frequency, making them essential for optoelectronic applications. This study presents a quantum chemical investigation into the effects of copper doping on the NLO properties of small gold clusters. Using density functional theory with the CAM-B3LYP/LanL2DZ level of theory, we examined both pure (Aum, where 8 ≤ m ≤ 10) and copper-doped (Aum-xCux) gold clusters. To the best of our knowledge, no theoretical studies have been reported on the nonlinear optical properties of pure and Cu-doped clusters. Copper incorporation leads to a marked reduction in the HOMO-LUMO energy gap from 4.77 eV down to 1.59 indicating enhanced NLO response. The dynamic NLO properties were computed at a standard Nd:YAG laser wavelength (1064 nm; ω = 0.0428 au). Among the doped clusters, Au1Cu8 exhibited the highest first hyperpolarizability β(-ω,ω,0), reaching 5.27 × 106 au. The second hyperpolarizability γ(-ω;ω,0,0) peaked at 3.89 × 107 au for Au4Cu5, while the third-order response γ(-ω;ω,0,0) was highest for Au2Cu8 at 1.03 × 1010 au. These results highlight copper-doped gold clusters as promising candidates for the development of high-performance NLO materials, with potential applications in next-generation electronic and photonic devices.