Enhanced room temperature excitonic luminescence in ZnO/polymethyl methacrylate nanocomposites prepared by bulk polymerization

Homogeneous ZnO/polymethyl methacrylate (PMMA) nanocomposites were prepared by incorporating ZnO nanoparticles synthesized in various diols into a PMMA matrix by the free-radical bulk polymerization. Room temperature photoluminescence spectra of the as-grown and PMMA-embedded ZnO nanoparticles exhibit an excitonic band-gap emission at 3.3 eV, a near band-gap emission at ∼3.1 eV and a broad defect band centered at ∼2.4 eV. Relative intensity of the defect versus band-gap luminescence depends on the parameters of ZnO preparation as well as the average particle size. However, PMMA-embedded particles produce a much stronger excitonic luminescence, whereas the ratio of the 3.1 to 2.4 eV remains approximately constant. There is no indication of random lasing threshold pointing to the ZnO/PMMA interfacial origin of the enhanced band-gap emission.