Synthesis of scheelite-type nanocolloidal particles by pulsed laser ablation in liquid and their size distribution analysis

Abstract

A novel pulsed laser ablation process in liquid was investigated to prepare scheelite-type ceramic [calciumtungstate (CaWO4) and calcium molybdate (CaMoO4)] nanocolloidal particles. The crystalline phase, particle morphology,particle size distribution, absorbance and optical band-gap were investigated. Stable colloidal suspensions consisting of welldispersedCaWO4 and CaMoO4 nanoparticles with narrow size distribution could be obtained without any surfactant.Particle tracking analysis using optical microscope combined with image analysis was applied for a fast determination ofparticle size distribution in the prepared nanocolloidal suspensions. The mean nanoparticle size of CaWO4 and CaMoO4colloidal nanoparticles were 16 nm and 30 nm, with the standard deviations of 2.1 and 5.2 nm, respectively. The opticalabsorption edges showed blue-shifted values about 60~70 nm than those of reported in bulk crystals. And also, theestimated optical energy band-gaps of CaWO4 and CaMoO4 colloidal particles were 5.2 and 4.7 eV. The observed band-gapwidening and blue-shift of the optical absorbance could be ascribed to the quantum confinement effect due to the verysmall size of the CaWO4 and CaMoO4 nanocolloidal particles prepared by pulsed laser ablation in liquid.