Structural, morphological and luminescence properties of hafnia nanoparticles obtained by hydrothermal synthesis

Hafnia is a novel material for optoelectronic applications, fabrication methods are focused to obtain hafnium oxide nanomaterials included thin films and nanoparticles. HfO2 nanoparticles synthesized and studied in this work are crystalline without subsequent heat treatment and were processed by hydrothermal method at 200 °C during 1.3, 2 and 4 h. SEM and TEM analysis revealed the presence of spherical and oval nanoparticles, with range size from 60 to 70 nm and 90–110 nm for spherical and oval nanoparticles, respectively. Raman spectroscopy and X-ray diffraction confirmed that nanoparticles exhibit a stable monoclinic phase. Crystal growth is typical with the presence of the characteristic monoclinic plane (1¯11) but for reaction times of 2 and 4 h and pH over 12 it turns in the plane (220) which is perpendicular to typical growth. Cathodoluminescence measurements revealed strong blue emission intensity showing a broadband in all visible range and a maximum peak at 460 nm. The presences of VO3 and VO4 in HfO2 crystalline structure are responsible for this inherent CL emission corroborated by photoluminescence studies.