Tunable emission properties of star-shaped ZnO-ZnS-SiO₂ composites synthesized by ultrasound-assisted Stöber method

ZnO-ZnS-SiO₂ composites were synthesized by an ultrasound-assisted Stöber method. The incorporation of blue-emitting ZnS on the surface of ZnO particles allowed the fabrication of a composite material with tunable emission. SEM pictures revealed star-shaped ZnO structures with a size about of 1 µm in length with multiple spindles. The composition of the materials was confirmed by EDS, FT-IR, and Raman spectroscopies. X-ray diffraction pattern analysis revealed that ZnO and ZnS have hexagonal wurtzite and cubic sphalerite crystal structures, respectively. The estimated band gap values of ZnS, ZnO, as well as the composites were 3.61, 3.13 and 3.21 eV, respectively. The emission spectrum of star-shaped ZnO exhibits a weak excitonic signal and a second intense and broad band centered around 620 nm. Photoluminescence analysis of the composites revealed a very broad emission band covering almost entirely the visible region of the spectrum and whose emission color ranges from orange to blue region of the CIE1931 chromaticity space, as the content of ZnS in the composite increases. Moreover, this tuning of the luminescence allows the generation of white light.