The role of Yb doped ZnO in the charge transfer process and stabilization

This work aims to investigate the role of Yb dopant in the ZnO photoactivity. A new material based on ZnO doped with a small amount of Yb (1% molar) has been synthesized, characterized and tested respect to an enhancement of the photoactivity via Electron Paramagnetic Resonance spectroscopy. The prepared material has been characterized via X Ray diffraction, UV visible spectroscopy and in particular with the transmission electron microscopy. The morphological analysis with high resolution TEM allowed us to identify the formation of a new species not visible with XRD and assigned to isolated Yb2O3 nanoparticles supported on the surface of larger particles of the more abundant zinc oxide phase. The as obtained material exhibits a band gap corresponding to UV light (≈3.3 eV), but nevertheless it shows a relevant photo-activity under irradiation with photons with λ > 420 nm (visible light). This phenomenon has been investigated by means of several methods. A specific EPR-based approach allowed to monitor and quantify the charge separation following the formation of holes in the valence band (VB) of the two materials.