Hafnium oxide powders were synthesized using the sol–gel method and further subjected to microwave treatment (MT) or conventional heat treatment (CT). The HfO2 powders were transformed into a monoclinic phase with a small crystallite size when using MT at 350 °C and CT at 450 °C. Both methods gave products possessing photoluminescence (PL) emission bands at approximately 415 and 523 nm. Furthermore, the intensity of the PL was found correlate to the treatment temperature and to the concentration of oxygen vacancies in the powders.
