On the origin of white photoluminescence from ZnO nanocones/porous silicon heterostructures at room temperature

• ZnO nanocones have been deposited on porous silicon without metallic nanocatalysts.
• The ZnO nanocones/porous silicon heterostructures emit white photoluminescence.
• The yellow and green emissions are related to oxygen and zinc vacancies.
• Surface traps in nanocones lead to weak UV emission and no g = 1.96 resonance.
• The g = 1.96 electron resonance is not related to visible emission from ZnO.

ZnO nanocones were grown on porous silicon (PS) by vapor transport at different temperatures and O2 flow rates without metal nanocatalysts. The ZnO/PS heterostructures were studied by electron microscopy, and by photoluminescence and electron resonance (EPR) spectroscopies. Samples emitted strong white PL, opening potential application for white light illumination. The photoluminescence spectra were found to include five main components centered at 1.84, 2.06, 2.30, 2.48 and 3.31 eV. The components at 2.48 and 2.06 eV were related to oxygen vacancies in ZnO, that at 2.3 eV to Zn vacancies and the one at 1.84 eV to the PS substrate. The low excitonic emission intensity at 3.31 eV and the observed rough ZnO nanocone morphology suggest the presence of surface trap states. EPR shows a g ∼ 2.006 line attributed to Zn divacancies. The absence of the g = 1.96 line, attributed to conduction band electrons, suggests strong carrier depletion.