Influence of laser wavelength on surface enhanced Raman spectroscopy using Mn based nano-particles produced by laser ablation synthesis in 4,4′ Bipyridine solution (LASiS)

In this work surface Raman spectroscopy of Mn based nano-particles produced by laser ablation technique in 4,4′ Bipyridine (Bipy: C10H8N2) aqueous environment is studied using three Raman spectroscopes with different laser wavelengths of 532, 632.8 and 785 nm. Transmission electron microscopy (TEM), X-ray diffraction (XRD), UV–visible spectroscopy (UV-Vis), dynamic light scattering (DLS) and Fourier transformations infra-red spectroscopy (FTIR) produced the characteristics of the obtained samples. Results of TEM and DLS showed that spherical Mn based nano-particles with a diameter of 40 nm and nano-rods with different lengths were produced. A value of − 23.61 mV for zeta potential and a mobility of − 1.84 × 10−8 m2s−1V−1 showed the instability of the produced nano-particles in the solution which can be stabilized by ultrasonic treatment of the solution. The absorption spectra showed two peaks at 400 and 422 nanometer wavelengths that may be assigned as transverse and longitudinal plasmonic oscillations of the nano-rod particles, respectively. The most intense peak in the XRD pattern of nano-particles in Bipy solution was assigned as MnO2(131) and no Mn peak was observed. Raman and FTIR analyses should not result in similar data for molecules with center of symmetry. This is confirmed in the results of this work for Bipy as such molecule. High enhancement of the Raman peaks of Bipy was achieved using all three different laser wavelengths. The influence of laser wavelength on different main Raman shifts of Bipy is discussed and related to the correlation between the laser wavelength and size of the nano-particles. In particular, and consistent with this and previous results some combined Raman shifts are also observed using 632.8 nm laser wavelength.