Tailoring the Emission Behavior of WO(3) Thin Films by Eu(3+) Ions for Light-Emitting Applications

The article reports the successful fabrication of Eu(3+)-doped WO(3) 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(3):Eu(3+) thin film system using RFMS. X-ray diffractograms revealed that the crystalline nature of these thin films increased upto 3 wt% of the Eu(3+) concentration. The diffraction peaks in the crystalline films are matched well with the monoclinic crystalline phase of WO(3), but for all the films’, micro-Raman spectra detected bands related to WO(3) monoclinic phase. Vibrational and surface studies reveal the amorphous/semi-crystalline behavior of the 10 wt% Eu(3+)-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(3+)-doping content. The doped films, except the one at a higher doping concentration (10 wt%), show unique emissions of Eu(3+) ions, besides the band edge emission of WO(3). With an enhancement of the Eu(3+) content, the concentration quenching process of the Eu(3+) 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(3+) ion concentration.