Zinc oxide nanoparticles smaller than about 7 nm in diameter exhibit the so-called quantum size effect, an enlargement of the band gap that is typically measured by the blue shift of light absorbance. This makes ZnO nanoparticles attractive in UV-protection films, chemical sensors and as stabilizer in polymers. The figure illustrates the optical absorbance spectra of as-prepared flame-made ZnO nanoparticles showing the blue shift associated with decreasing crystallite size. Co-precipitation with amorphous silica was used to control the crystallite size of d=3, 4, and 12 nm corresponding to molar ratios of X=0.80, 0.89, and 1, respectively.
Supported by Swiss National Science Foundation and Commission for Technology and Innovation (CTI).
Recent, relevant references:
- Mädler, L., Stark, W. J., and Pratsinis, S. E. "Rapid Synthesis of Stable ZnO Quantum Dots", J. Appl. Phys. 92, 6537-6540 (2002).
- Tani, T., Mädler, L., and Pratsinis, S. E. "Synthesis of Zinc Oxide/Silica Composite Nanoparticles by Flame Spray Pyrolysis", J. Mater. Sci., 37, 4627-4632 (2002).