Enhanced visible-light absorption from PdO nanoparticles in nitrogen-doped titanium oxide thin films

Composite films were made by embedding nanoparticles of p-type PdO semiconductor in a n-type titanium oxide matrix. With the assistance of nitrogen ion beam, these PdO nanoparticles were confined to less than a couple of nanometers. The resulting nanocomposite films demonstrated an unusual “redshift” in the optical absorption spectrum, contrary to the well-known quantum size effect from semiconductor nanoparticles. The absorption in the visible-light range is shown to result from absorption by metallic-like nanoparticles as palladium changed its valence state from Pd2+ to Pd in nitrogen-doped titanium oxide matrix under visible-light illumination.