Magnetic properties of rare earth doped ZnO nanoparticles: A comprehensive study via Magnetization and EPR

Abstract

This study presents the synthesis and characterization of rare earth (RE)-doped zinc oxide (ZnO) nanoparticles with an average particle size in the 10 nm range. The resulting nanostructures exhibit the wurtzite phase of ZnO, attributed to their preferential anisotropic growth along the polar c-axis. Upon excitation of the ZnO host within the bandgap region, visible luminescence intensity increases with rising RE³⁺ concentrations. This emission is primarily attributed to various intrinsic and extrinsic defect states within the host lattice. Energy transfer from these defect centers to RE³⁺ dopant sites facilitates characteristic luminescence. Specifically, efficient intra-4f orbital transitions (⁵D₄ → ⁷Fⱼ) of Tb³⁺ ions result in distinctive green and red emissions. Furthermore, modulation of defect states and decay rates of RE³⁺ transitions enables temporal control over the emission profile, allowing for selective generation of red or pure green light. This work highlights the potential of defect engineering via bottom-up synthesis methods to tailor energy transfer dynamics, offering promising avenues for the development of multicolor emission displays and ZnO-based optoelectronic phosphor devices. In addition to their optical applications, RE-doped ZnO nanoparticles exhibit unique physicochemical and biological properties that contribute to sustainable agricultural practices. These nanoparticles enhance plant tolerance to abiotic stresses such as drought, salinity, and heavy metal contamination by boosting antioxidant enzyme activity and immobilizing toxic metals. From a sustainability perspective, their use promotes reduced environmental contamination, improved nutrient use efficiency, and lower dependence on chemical inputs, thereby supporting eco-friendly and resource-efficient agriculture.