Solvent-dependent tuning of blue–green emission of chemically synthesized ZnO nanomaterials with high colour purity and electroluminescence efficiency

A series of nanomaterials of ZnO have been synthesized via chemical co-precipitation method with fixed proportions of precursors and varied solvents. X-ray diffraction confirms wurtzite crystalline structure with nanometric crystallites (< 23 nm). Texture coefficient of crystallographic orientations show remarkable change for switching the solvents from water to alcohol. Morphological study reveals nanomaterials resembling prolate, sphere and oblate shaped structures for the solvents water, methanol and ethanol, respectively, with increasing particle size. All the nanomaterials show a similar absorption band in the UV region; though, more absorption covering a wider region in visible range is observed for nanomaterials prepared in alcoholic solutions. Red shifting in band gap of nanomaterials is correlated with band-tail effect. Variation in Urbach energy indicates that the nature of solvent plays a vital role in creating defects in ZnO, justifying enhanced absorptions in visible region. Photoluminescence (PL) spectra show various emission bands consisting of blue, green and yellow emissions corresponding to different intrinsic defects in nanomaterials. PL displays a tuning trend for blue–green emission by changing solvent from water to alcohol. However, overall enhanced PL intensity and particularly intense blue emission have been achieved by replacing water with alcohol. Tunability in emission colours and high colour purity is observed in the CIE chromaticity analysis. Theoretically, estimated electroluminescence of ZnO prepared in alcohol shows superiority compared to ZnO prepared in water. The mechanism of solvent-mediated defect creation and emission in ZnO will be beneficial for future QD LED applications.