Enhanced near-infrared luminescence in zinc aluminate bestowed by fuel-blended combustion approach

Fuel-blend combustion method using urea and monoethanolamine (MEA) fuels, is employed to tune the defect states and hence luminescence properties of nanocrystalline ZnAl2O4. Prepared nanocrystals flaunt a ravishing blue and intensified near-infrared (NIR) emission with varying intensities. Sample prepared using 80% MEA blended with 20% urea exhibits highest NIR emission, seven-fold intense than that prepared by 100% MEA, attributed to larger amount of deep band gap defects. Presence of multiple defects viz. vacancies of zinc, aluminium and oxygen is probed by means of Rietveld refinement, X-ray absorption near edge spectroscopy and photoluminescence spectroscopy. Band tailing and presence of shallow defect states are indicated by optical band gap and Urbach energy values. Broad range visible to NIR emission envisages application of ZnAl2O4 nanocrystals for bioimaging purposes. Radiative transitions among various defect levels contributing toward the emission have been depicted through a band model diagram. (C) 2019 Elsevier B.V. All rights reserved.