Highly transparent bulk PMMA/ZnO nanocomposites with bright visible luminescence and efficient UV-shielding capability

We demonstrate a valuable two-step in situ polymerization process to address the four key issues on preparation of the bulk PMMA/ZnO nanocomposites, that is, transparency, luminescence, UV shielding capability, and homogeneity, since in all previous reports it is hard to give attention to four, or any three and even two of the above properties. Step 1 is the in situ sol-gel polymerization process, involving the nucleation and growth of ZnO quantum dots (QDs) in ethanol solutions. In this step, the ZnO QDs were formed along with the copolymerization of MMA monomers and zinc methacrylate (Zn(MAA) ₂). The obtained PMMA/ZnO precursors emit bright blue and yellow luminescence. Then in Step 2, the precursors are further polymerized into PMMA matrices to get the final bulk PMMA/ZnO nanocomposites that show high transparency, bright visible luminescence, efficient UV-shielding capability, and good homogeneity. The quantum yields of the ZnO QDs could reach as high as 60% for the blue light emitting samples and 30% for the yellow light emitting ones. Finally, the careful spectral characterization indicates that the oxygen vacancies that are the main existing defects states in the quantum sized ZnO particles are probably responsible for the visible luminescence of our ZnO QD samples.