Biocompatible reagent-free ZnO nanoparticles with controlled luminescence for anti-counterfeit inks

Abstract

ZnO nanoparticles exhibit remarkable versatility due to their broad spectrum of physical and chemical properties, enabling their use in diverse fields ranging from device fabrication to biomedical applications. To harness their luminescent properties, methods such as doping and chemical synthesis are commonly employed. In this study, we present a novel approach for controlled defect engineering in pristine ZnO nanoparticles via the femtosecond laser ablation technique. Enhanced photoluminescence and cathodoluminescence were achieved in nanoparticles with a similar size distribution as the pulse power was increased from 0.25 W to 1.5 W. Raman spectroscopy confirmed a clear signature of increase in oxygen vacancies correlating with increasing ablation power. Additionally, a mechanism is proposed to explain the change in the deep-level emission observed in the photoluminescence and cathodoluminescence spectra, elucidating the effect of electron beam excitation. Specifically, we demonstrated the photoluminescence emission of ZnO nanoparticles on paper, exhibiting fluorescence in the visible range upon excitation within 270–360 nm. The tunable photoluminescence emission of similarly sized nanoparticles under UV light makes them highly suitable for anticounterfeiting applications.