Plasmon Enhancement Effect in Au Gold Nanorods@Cu2O Core–Shell Nanostructures and Their Use in ProbingDefect States.

Au@Cu2O core–shell nanostructures are fabricated to havea plasmon enhancement effect using Au nanorods (Au NRs) as a plasmon-tailorablecore. By varying the concentration of Au NRs, we can tune the shellthickness in the range of 10–25 nm. The shell is composed ofCu2O nanocrystallites. Because of the thin shells, theextinction spectra at wavelength >500 nm are dominated by the Aucore. However, the large dielectric constant of the shell causes anobvious red shift of the surface plasmon resonance (SPR) band of theAu nanorod. Besides, transverse octupolar SPR appears as a resultof the anisotropy of the core and the high dielectric constant ofthe shell. The anisotropic geometry of the Au NR is found to supportthe octupolar resonances at smaller sizes than for their sphericalcounterpart. Theoretical simulations indicate that the transverseSPR bands are divided into two resonances, which are dipolar- andoctupolar-dominant, respectively. The Cu2O shell degradesvia a defect-mediated oxidative pathway, which is aggravated uponlongitudinal SPR excitation. The SPR-mediated local field enhancementand resonance energy transfer are found to enhance the excitationof the defect states in the shell, thus providing a simple yet selectiveprobing strategy for defect states. [ABSTRACT FROM AUTHOR]