Optical Properties of Zinc Aluminate, Zinc Gallate, and Zinc Aluminogallate Spinels

Abstract

The optical spectra of zinc aluminate (ZnAl 2 O 4 ), zinc gallate (ZnGa 2 O 4 ), and zinc aluminogallate (ZnAlGaO 4 ) spinel powders were studied at wavelengths in the range of 250‐900 nm using reflectance spectroscopy. The ZnAl 2 O 4 and ZnGa 2 O 4 powders were synthesized by using conventional ceramic processing techniques and had systematic variations in the molar ratio of ZnO to M 2 O 3 (M = Al or Ga). The cubic spinel crystal structure of each composition was confirmed via powder X‐ray diffractometry. The ZnAl 2 O 4 powders showed optical properties in the ultraviolet wavelength region and had combined characteristics that were similar to that of ZnO (wurtzite structure) and Al 2 O 3 (corundum structure), which result from the similar local environments of the zinc and aluminum cations within the cubic spinel crystal structure. A mechanically induced optical absorption (optomechanical effect) in the ultraviolet wavelength region was also observed in ZnAl 2 O 4 . The ZnGa 2 O 4 powder followed a similar behavior, with the exception that the optomechanical effect did not occur in the gallate. The ZnAlGaO 4 showed optical spectra that were intermediate to that of the endpoint compositions.