Study of blue-light emission properties of WO3:Eu microstructures

Abstract

Structural, surface morphological, optical absorption and emission properties of 0–5% Eu doped WO3 samples are studied. The samples are synthesised by acidic precipitation method. The structural analysis reveals that the sample has ‘room-temperature monoclinic’ structure. The average crystallite size of the undoped sample is ∼58.57 nm and it decreases to 34.72 nm after doping of Eu at 5%. The undoped sample has hexagonal disc-like grain structures with average diameter of ∼0.84 μm. All the samples show a sharp absorption edge above 350 nm. The transmittance of the samples increases above 400 nm and reaches its maximum at ∼490 nm. The extinction coefficient of the undoped sample is minimum at 390 nm and it has a relatively smaller value than that of the doped samples. The optical bandgap of the undoped sample is found to be 3.56 eV and it decreases to 3.28 eV with the increase of concentration of Eu to 5%. Analyses of PL spectra show that the undoped sample under 355 nm UV excitation produces a broad blue emission band with five maxima at ∼403, 414, 435, 473 and 495 nm due to band-to-band transitions and transitions involving intrinsic defects. A blue emission band centred at ∼435 nm is increased by two-fold after doping of Eu at 1%. In addition, a secondary emission band is found at ∼505 nm due to formation of an aggregate defect (F2 centre). When the doping concentration is increased to 5%, another secondary band is observed at 610 nm due to interstitial Eu3+ centre. The enhancement of the blue emission band is attributed to formation of oxygen vacancies due to substitution of W6+ ions by Eu3+ ions. The enhanced blue light in the sample doped with 1% of Eu has potential application in WLED as well as other light emitting applications.