Hi Parinaz,

Check out the link below.

Regards.

http://www.sigmaaldrich.com/materials-science/nanomaterials/gold-nanoparticles.html

Dear Parinaz,

From my experiments on gold nanofluids, maximum absorption is at ~530 nm light wavelength.

Dear Abdullah and Aimen,

Thank you for your responses, but I think I need to make my question more clear:

Is the frequency at which extinction peak appears different from the frequency at which the nanoparticle has its maximum field enhancement?

Thanks,

Maximum field enhancement is provided at the frequency of the plasmon peak. This can shift from 518 to 590 nm depending on size and aggregation state of the particles. In the case of nanorods there are two plasmon peaks, the transversal and the longitudinal plasmon resonance. Both can give field enhancement. The longitudinal peak can be shifted into the near IR. In summary, for optimal field enhancement it makes sense to chose a laser wavelength that is as close as possible to the plasmon absorption peaks of the system.

The wavelengths of highest extinction and of highest field enhancement are related but not exactly the same. I recommend the supplementary information of this article: Khatua, S., Paulo, P. M. R., Yuan, H., Gupta, A., Zijlstra, P., & Orrit, M. (2014). Resonant Plasmonic Enhancement of Single-Molecule Fluorescence by Individual Gold Nanorods. ACS Nano, 8(5), 4440-4449. From Figure S3 you can see the difference.