Role of the surface polarity in governing the luminescence properties of ZnO nanoparticles synthesized by Sol–gel route

ZnO nanoparticle samples, which are synthesized by a sol–gel route and collected after various stages of a washing procedure, are systematically investigated using a variety of experimental techniques. The study shows that while the surface charge polarity is positive for the as-grown (unwashed) particles, the surface turns negatively charged when the particles are sufficiently washed. This dissimilar surface charge polarity has been found to result in markedly different luminescence characteristics for the two cases (washed and unwashed). Our study of the luminescence properties under different surrounding conditions furthermore reveals that the major source for the GL emission for these nanoparticles is the hydroxyl groups, which are physisorbed on the surface.