Exciton-mediated surface-enhanced Raman studies of Aluminum doped platinum nano colloids

Abstract

In this article, we report the fabrication of Aluminum doped Platinum bimetallic nanoparticles (NPs) by ultrafast laser ablation (using femtosecond laser pulses of duration ∼50 fs, central maximum 800 nm) of Aluminum (Al) target immersed in Platinum (Pt) colloidal solutions in Isopropanol. Colloidal solutions of Pt NPs at a concentration of 0.5 mM, 1 mM, 3 mM, and 7 mM were prepared in Isopropyl alcohol and exhibited localized surface plasmon resonances (LSPR) at ∼292 nm. However, the LSPRs of Al-doped Pt colloids were modified to ∼283 nm (0.5 mM Pt), ∼226 nm (1 mM Pt) ∼226 nm (3 mM Pt) ∼228 (7 mM Pt). Average sizes of Al-doped Pt colloidal NPs synthesized by the ablation of Al metal targets immersed in 0.5 mM Pt, 1 mM Pt, 3 mM Pt, and 7 mM Pt colloids were estimated to be ∼19.5 nm, ∼11 nm, ∼12 nm, and ∼13.5 nm, respectively. These Al-doped Pt NPs are employed in surface-enhanced Raman scattering (SERS) studies of Methylene Blue (MB) dissolved in IPA at 0.5 μM, 5 μM, and 50 μM concentrations. Although the SPR strength of Pt and Al are moderate, the annihilation of the excitons created in Al-doped Pt NPs might lead to the formation of the charge carriers, enhancing the population in the conduction band and strengthening the SPR, finally leading to a significant SERS enhancement. The estimated enhancement factors for the mode 1623 cm−1 correspond to MB's highly elevated vibrational mode are ∼105. This article is the first report of its kind on SERS of Al-doped Pt NPs to the best of our knowledge.