Microwave-assisted ionic-liquid-based synthesis of highly crystalline CaMoO₄: RE³⁺ (RE combining double low line Tb, Sm, Eu) and Y₂Mo₄O₁₅:Eu³⁺ nanoparticles

Fluorescent CaMoO₄:RE³⁺ (RE Combining double low line Tb, Sm, Eu) nanoparticles, 50-70 nm in diameter, were prepared via a microwave-assisted synthesis in ionic liquids. Herein, the ionic liquid allows heating to high temperatures in the liquid phase (200 °C), which guarantees for an optimal crystallization of the nanoparticles. All nanoparticles were indeed readily crystalline without the need of any additional powder sintering. Especially, CaMoO₄:Tb and CaMoO₄:Eu exhibit high quantum yields of 52% and 82% under UV-excitation (300-320 nm). All compounds were characterized by electron microscopy (SEM), dynamic light scattering (DLS), infrared spectroscopy (FT-IR), energy-dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and fluorescence spectroscopy (FL). In order to shift the excitation to even higher wavelengths, Y₂Mo₄O₁₅:Eu was firstly realized as a nanomaterial, again, using the microwave-assisted synthesis in ionic liquids. Y₂Mo₄O₁₅:Eu exhibits a particle size of 25-30 nm, and shows a high quantum yield of 67%, too. As this nanomaterial can be excited up to 400 nm, it represents one of the first efficient red-emitting, Eu³⁺-doped nanomaterials for near-UV excitation (>350 nm) with a simple, low-cost UV-LED. This can be relevant for all kinds of thin-film applications as well as for optical imaging.