Luminescence enhancement in nanocrystalline Eu2O3 nanorods - Microwave hydrothermal crystallization and thermal degradation of cubic phase

Thermally induced crystallization of cubic Eu2O3 obtained with the microwave hydrothermal method has been investigated. The starting material crystallized in the form of needle-shaped agglomerates of nanocrystalline hexagonal Eu(OH)3. Thermal treatment up to 800 °C induced the crystallization of cubic Eu2O3, after further calcination at 1200 °C in the air a monoclinic phase appeared. The phase transformation caused abnormal reduction of Eu3+ ions, related to the oxygen vacancy creation during sintering of the oxide crystallites. The crystallization process of cubic Eu2O3 occurred within the agglomerates without change of their shapes. The cubic form exhibited bright emission of Eu3+ related luminescence with intensity increasing with the size of crystallites.