Surprising Eutectics: Enhanced Properties of ZnO-ZnWO4 from Visible to MIR

Abstract

Zinc oxide-zinc tungstate (ZnO-ZnWO₄ ) is a self-organized eutectic composite consisting of parallel ZnO thin layers (lamellae) embedded in a dielectric ZnWO₄ matrix. The electromagnetic behavior of composite materials is affected not only by the properties of single constituent materials but also by their reciprocal geometrical micro-/nano-structurization, as in the case of ZnO-ZnWO₄ . The light interacting with microscopic structural features in the composite material provides new optical properties, which overcome the possibilities offered by the constituent materials. Here remarkable active and passive polarization control of this composite over various wavelength ranges are shown; these properties are based on the crystal orientation of ZnO with respect to the biaxiality of the ZnWO4 matrix. In the visible range, polarization-dependent polarized luminescence occurs for blue light emitted by ZnO. Moreover, it is reported on the enhancement of the second harmonic generation of the composite with respect to its constituents, due to the phase matching condition. Finally, in the medium infrared spectral region, the composite behaves as a metamaterial with strong polarization dependence.

Keywords: ZnO; ZnWO 4; eutectics; metamaterials; optical luminescence; second harmonic generation.