Preparation of monodisperse ZnO/SiO₂ composite particles using spray drying with an anionic surfactant template and their photoluminescence characteristics

The photoluminescence (PL) characteristics of ZnO/SiO₂ composite particles were investigated. ZnO/SiO₂ composite particles were synthesized utilizing the consecutive sol–gel spray drying method by incorporating sodium lauryl sulfate (SLS) as a particle morphology control agent. The effect of SLS concentration and ZnO ratio on precursors was studied further on the composite particle morphology and PL performance. Elevating the SLS concentration exhibited a reduction in the particle diameter and an increase in particle uniformity. The particle diameter without SLS was 6.18 µm and reduced to 2.6 µm with the addition of SLS at 3 critical micelle concentrations (CMC). The decrease in ZnO concentration also reduced the particle diameter of the ZnO/SiO₂ composite to 1.74 µm at a ZnO concentration of 25% mol. In addition, the increase in the excitation wavelength from 230 nm to 320 nm indicates a shift in the peak emission intensity at higher wavelengths from 467 nm to 645 nm. The excitation wavelength-dependent photoluminescence phenomenon was exhibited by incorporating silica into the ZnO precursor pre- and post-drying to deliver composite particles. The addition of silica to the composite particles can augment the PL emission intensity without causing a shift in the PL emission peaks when excited at the same wavelength. The 25% mol ZnO composite particles with the addition of SLS 3 CMC had the highest PL emission intensity. The amount of silica nanoparticles sufficient to trap the ZnO nanoparticles in the droplet is an important factor besides the size and uniformity of the particles, which causes the high intensity of PL emission.