Surface optical phonon and multi - phonon transitions in YVO4: Eu3+ nanopowders

Abstract

In this paper two methods of preparation of yttrium orthovanadate nanopowders were presented: Solid State Reaction (top - down approach) and Solution Combustion Synthesis (bottom - up approach). For starting structural characterization, X - Ray Powder Diffraction (XPRD) and Field Emission Scanning Electron Microscopy (FESEM) were used. We report the change in reflection spectra in europium doped YVO4 nanopowders with comparison to its bulk analog. In UV-Vis reflection spectra we consider the change in values of band gap in these structures, after resizing it from bulk to nanomaterial. In Far - Infrared (FIR) reflection spectra, we registered the existence of Surface Optical Phonon (SOP) and different multi - phonon processes which alter the reflection spectra of bulk YVO4 . The influence of Eu ions is reflected through multi - phonon processes that occur and are connected with energy transfer from YVO4 lattice to Eu ions. All IR spectra were modeled using classical oscillator model with Drude part added which takes into account the free carrier contribution. Since our samples are distinctively inhomogeneous materials, we use Effective Medium theory in Maxwell Garnett approximation to model its effective dieletric function.