Effect of Eu ³⁺ ion concentration on optical and magnetic properties of oriented Gd ₂ O ₃ /CTAB nanoparticles as multifunctional optical-magnetic probes in biomedicine

The Gd₂O₃:Eu³⁺ nanoparticles were synthesized using a multi-step chemical method with urea as a reactant to control the ratio of different Eu³⁺ activation centers: 2, 4, 6, 8, 10, and 12 mol% combined with CTAB surfactant to improve surface quality. The study aimed to determine the optimal concentration of Eu³⁺ in the presence of CTAB to increase biocompatibility and achieve the best fluorescence. The structure, surface morphology, optical properties, and magnetic properties of the materials were analyzed through FSEM, XRD, HRTEM, XPS, UV-vis, fluorescence, fluorescence excitation, time-resolved fluorescence, vibrating sample magnetometry (VSM), and magnetic heating measurements. The obtained material had a diameter of 180-280 nm, and it emitted red light with characteristic shifts from ⁵D₀ to ⁷F _<i>J</i> (<i>J</i> = 0-4). The strongest emission peak occurred at the transition of ⁵D₀ to ⁷F₂, corresponding to a wavelength of 611 nm. The crystal is in the cubic phase. The highest lifetime of the samples is 2.1 ms, and the highest calculated quantum efficiency is 91% for the Gd₂O₃:8% Eu³⁺ sample. The M-H hysteresis curve revealed that the highest magnetic field obtained was 1.83 emu g^-1. Experimental induction heating of samples reached temperatures in the range of 44-49 °C, which is an appropriate temperature range for destroying cancer cells without affecting healthy cells. These findings demonstrate that the material has great potential in cancer diagnosis and treatment.