Defect induced broadband visible to near-infrared luminescence in ZnAl2O4 nanocrystals

Materials emitting over a broad range of wavelengths have been gaining attention consistently owing to their potential applications. ZnAl2O4 has been an attractive material due to its robust luminescence properties. Herein, we report white and intense near-infrared emission, simultaneously, in undoped ZnAl2O4 nanocrystals at a relatively lower temperature (550 degrees C) than reported earlier. Emission is accompanied by various types of shallow and deep donor/acceptor defects, for instance, ionic vacancies and antisite defects existing in the crystal lattice. Switching of white to blue color is observed with annealing owing to rearrangement of defects. Rietveld refinement of X-ray diffraction patterns confirm the presence of multiple defects in the crystal lattice. Transmission electron microscopic analysis has revealed the change in morphology from spherical to polyhedron and increase in crystallite size on annealing. Suitable values of illuminating engineering society colorimetric parameters such as fidelity index, luminous efficiency of radiation, color gamut etc. predict its potential applications in lighting and bioimaging.