Multi-functional GdEu _x Tb _{1− x} O ₃ ( x = 0 to 1) nanoparticles: colour tuning optical properties, water proton spin relaxivities, and X-ray attenuation properties

Multi-functional nanoparticles are useful for various applications, such as biomedical imaging, detection, and display technologies. Colour-tunable GdEu_xTb_1-xO₃ nanoparticles were synthesized with emission colour ranging from green (545 nm) to red (616 nm) by varying x (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1). These nanoparticles were surface-grafted with polyacrylic acid and a small quantity of 2,6-pyridinedicarboxylic acid. This modification aimed to ensure long-term colloidal stability (>1 year without precipitation) and high quantum yields (>30%) in aqueous media. Additionally, they exhibited long emission lifetimes (∼1 ms), high longitudinal water proton spin relaxivities (>30 s^-1mM^-1), and high X-ray attenuation efficiencies (∼10 HU mM^-1). These multiple exceptional properties within a single nanoparticle make them highly valuable for applications in biomedical imaging, noise-free signal detection, and colour display.