White light phosphorescence from ZnO nanoparticles for white LED applications†
Abstract
White light emission from a pristine, solid material is currently the biggest challenge in the lighting industry. In this paper we report for the first time highly reproducible, stable, and intense white phosphorescence (∼4–32 μs) from phase-pure zinc oxide (ZnO) nanopowder synthesized by a simple, low temperature process. The structure and morphology were studied by XRD, FESEM, and TEM. The white light consisted of narrow blue (centered at ∼425 nm) and broad yellow-orange (centered at ∼625 nm) photoluminescence and the best result was observed at (0.36,0.33) in the CIE plot. The presence of zinc interstitial (Zni) and oxygen interstitial (Oi) defects responsible for such white phosphorescence was confirmed by EDX, XPS, and Raman studies. The visibly bright white emission has appreciable quantum yield (∼12–14%) and cool/near cool correlated color temperature, rendering it suitable for W-LED applications. Further, a defect chemistry-based thermodynamic interpretation was invoked to adequately explain the white emission.