Modelling of the optical absorption spectra of PLAL prepared ZnO colloids

We analyze the UV-vis absorption spectra of zinc oxide water colloids, prepared by pulsed laser ablation in liquids (PLAL), through a theoretical approach based on the multipole expansion of the electromagnetic fields and the transition matrix method. We reproduce the optical behaviour of these colloidal solutions also at wavelengths shorter than the one at the absorption edge. We extend our analysis to estimate the particle concentration taking into account the size distribution of the colloidal dispersion of the ZnO spherical nanoparticles. Moreover, we study the pulsed laser irradiation effects on the UV-vis absorption spectra of ZnO nanocolloids. Laser irradiation changes the morphological rearrangement of the ZnO nanoparticles. We are able to discriminate whether the irradiated sample is characterized by nanostructures with large or small aspect ratio. In this way, information about particle size distribution, concentration, and morphology can be obtained without performing any morphological characterization.

► ZnO nanocolloids were synthesized by pulsed laser ablation. ► Structural and optical properties are investigated. ► The sample's morphology is sensitive to the post-preparation laser irradiation. ► Estimate of the zinc oxide nanoparticles concentration. ► Large and small aspect ratio nanostructure discrimination.