Tailoring the Emission Behavior of WO Thin Films by Eu Ions for Light-Emitting Applications.

The article reports the successful fabrication of Eu-doped WO thin films via the radio-frequency magnetron sputtering (RFMS) technique. To our knowledge, this is the first study showing the tunable visible emission (blue to bluish red) from a WO:Eu thin film system using RFMS. X-ray diffractograms revealed that the crystalline nature of these thin films increased upto 3 wt% of the Eu concentration. The diffraction peaks in the crystalline films are matched well with the monoclinic crystalline phase of WO, but for all the films', micro-Raman spectra detected bands related to WO monoclinic phase. Vibrational and surface studies reveal the amorphous/semi-crystalline behavior of the 10 wt% Eu-doped sample. Valence state determination shows the trivalent state of Eu ions in doped films. In the 400-900 nm regions, the fabricated thin films show an average optical transparency of ~51-85%. Moreover, the band gap energy gradually reduces from 2.95 to 2.49 eV, with an enhancement of the Eu-doping content. The doped films, except the one at a higher doping concentration (10 wt%), show unique emissions of Eu ions, besides the band edge emission of WO. With an enhancement of the Eu content, the concentration quenching process of the Eu ions' emission intensities is visible. The variation in CIE chromaticity coordinates suggest that the overall emission color can be altered from blue to bluish red by changing the Eu ion concentration.