Facile synthesis, photoluminescence properties and microwave absorption enhancement of porous and hollow ZnO spheres

Three-dimensional (3D) porous ZnO nanostructures were synthesized via one-pot solvothermal treatment. The structural, morphological and spectral properties were investigated using X-ray diffraction (XRD), N₂ sorption measurement, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectroscopy. It was found that the minimum reflection loss value of ZnO calcined at 500°C reached -5.62dB at 16.24GHz with the thickness of 2.5mm, which had a superior performance of microwave absorption than those uncalcined and calcined at 600°C. The possible mechanism for the formation of porous ZnO hollow spheres was proposed. The relationship of the ZnO microstructure and the microwave absorption properties was revealed via studying the dielectric loss and interference multi-reflection absorption in this paper as well. In addition, the photoluminescence results show that the uncalcined ZnO and porous hollow ZnO calcined at 500°C and 600°C show a narrow and sharp UV emission at 355.8nm and a relatively broad visible spectra emission at around 423nm.