Study of active surface defects in Ti doped ZnO nanoparticles

The effects of surface defects (oxygen vacancies) on the electronic structure and photoluminance properties of titanium doped ZnO nanoparticles are reported. Nanoparticles of different sizes ranging from 6 to 25 nm are characterized by x-ray diffraction, Transmission electron microscopy, x-ray photoemission spectroscopy, and photoluminescence (PL) spectra. Structural analysis indicates that Ti ions are substituted at Zn sites in ZnO matrix. Surface defects are systemically increasing with decreasing the particles size, which is also confirmed by Raman scattering measurements. The intensity of the visible peak in the PL spectra exhibits an apparent nonmonotonic change over the entire range of the particle size. The intensity is shown to be decreasing with increasing the particle size but then increasing above a typical particle size of 15 nm. This nonmonotonic profile of visible intensity could be explained via two different mechanisms such as: (i) hole-trapped tunneling in smaller size particles and (ii) surface depletion region containing a rich amount of doubly charged oxygen vacancy (V-O(2+)) in the bigger size particle. (c) 2010 American Institute of Physics. [doi:10.1063/1.3432571]