Metastable polymorphs and luminescence of boehmite-derived alumina doped with divalent europium ions

The control of polymorphism transition of Eu2+ ion-doped gamma-, delta-, theta- and alpha-metastable alumina derived from boehmite is demonstrated by the sol-gel method through controlling the doping amount and firing temperature and the resultant luminescent properties are investigated. Nanosized boehmite (gamma-AlOOH) particulates in boehmite sol effectively prevent the formation of impurity phases of EuAlO2 and Eu2O3. The polymorphic structures of the induction-fired xerogel samples in weak reductive atmosphere can be held to the room temperature upon cooling down naturally. The luminescence properties of Eu2+ ions verify the polymorphic transitions from gamma-, delta-, theta- to alpha-Al2O3 that are featured with their broad emission peaks positions at 410, 450, 480 and 500 nm, respectively. It is believed that boehmite sol-gel by taking the nanosized gamma-AlOOH particulates as seeds assisted the dispersion of precursor constituents and is effective to adjust the onset of polymorphic transition temperatures and luminescence properties.