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

• Ionic-liquid-based synthesis of fluorescent CaMoO4:RE3+ (RE = Tb, Sm, Eu) and Y2Mo4O15:Eu nanoparticles.
• Microwave heating used for fast crystallization at low degree of agglomeration.
• Full-color emission with CaMoO4 (blue), CaMoO4:Tb (green), CaMoO4:Sm (orange), CaMoO4:Eu (red) and Y2Mo4O15:Eu (red).
• High quantum yields achieved for CaMoO4:Tb (52%), CaMoO4:Eu (82%), and Y2Mo4O15:Eu (67%).

Fluorescent CaMoO4:RE3+ (RE = 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.

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