Self-assembly and photoluminescence of molybdenum oxide nanoparticles

We report on the synthesis of self-assembled hillock shaped MoO3 nanoparticles on thin films exhibiting intense photoluminescence (PL) by RF magnetron sputtering and subsequent oxidation. MoO3 nanocrystals of size ∝29 nm are self-assembled into uniform nanoparticles with diameter ∝174 nm. The mechanism of the intense PL behaviour from MoO3 nanoparticles is investigated and systematically discussed. The films exhibit two bands; a near-band-edge UV emission and a defect related deep level visible emission. The enhancement in PL intensity with annealing is not only by the improvement in crystallinity and grain size but also by the increase in the rms surface roughness and porosity of the films. The PL intensity is thermally activated with activation energy 1.07 and 0.87 eV respectively for the UV and visible emissions. The UV band exhibits a blue shift according to the band gap with increasing post-annealing temperatures, which suggests the possibility to tune the UV photoluminescence band by varying the oxidation temperature. (orig.)