Eu-Doped YPO4 Luminescent Nanopowders for Anticounterfeiting Applications: Tuning Morphology and Optical Properties by a Rapid Microwave-Assisted Hydrothermal Method

In this work, a rapid microwave-assisted hydrothermal method under mild conditions is investigated for the preparation of the Eu3+:YPO4 (5 mol % Eu) luminescent material, which belongs to a large family of phosphates that, when doped with lanthanide ions, acquire specific luminescence properties used primarily as phosphors for modern light sources and as optical markers. Crystalline Eu3+:YPO4 nanopowders are obtained in very short times (as little as 5 min) compared to conventional methods without the need for additional calcination treatment. Moreover, varying the reaction time (up to 30 min) and temperature (up to 240 °C) results in different nanocrystal morphologies and sizes, which can be tuned by controlling the reaction parameters, thus potentially tuning the optical properties of the nanoparticles. The resulting nanopowders exhibit intense emission at an excitation wavelength of 396 nm, and their optical properties, studied by measuring both excitation and emission spectra, luminescence lifetimes, and quantum yields, are comparable to those obtained by conventional heating. These results suggest that the MW-assisted hydrothermal process optimized in this work is a powerful strategy to produce single-phase Eu3+:YPO4 (5 mol % Eu) luminescent nanopowders with a low degree of hydration, monodisperse tuned morphology and narrow particle size distribution in much shorter times than previously reported (5-30 min). So we have developed a faster and more energy-efficient way of producing these materials, which could potentially be used for security purposes.