Optical influence of annealing in nano- and submicron-scale ZrO2 powders

Nano- and submicron-scale crystalline ZrO2 powders with a monoclinic phase were comparatively investigated as a function of annealing temperature. The energies of defect states may change upon annealing, leading to the variations in crystallite size as revealed in X-ray diffraction and forming the excessive nano-crystallites aggregation as revealed in scanning electron microscopic images. The concomitant electronic energy states are identified by measuring photoluminescence excitation and photoluminescence spectra in UV and visible range and related with abundant oxygen vacancies as a function of annealing temperatures. The crystallites aggregation upon annealing was further manifested by the size-dependent extinction coefficients at 0.2–1.6 THz.