Hydrothermal formation and characteristics of rare-earth niobate phosphors and solid solutions between YNbO4 and TbNbO4

• Niobate:YNbO4:Tb3+ nanocrystals were directly formed via hydrothermal route.
• The complete solid solutions between YNbO4 and TbNbO4 were directly formed.
• The optical band gap decreased from 3.6 to 2.9 eV with increased Tb content.
• The nanocrystals doped with Tb3+ emitted blue (490 nm) and green (545 nm) light.
• The highest PL intensity was obtained (Y0.9Tb0.1NbO4, via heating at 1300 °C).

Monoclinic fergusonite-type niobate, YNbO4:Tb3+ and complete solid solutions with luminescent properties in the YNbO4–TbNbO4 system were directly formed as nanocrystals from the precursor solutions of NbCl5, TbCl3, and YCl3 under hydrothermal conditions at 240 °C. The niobate nanocrystals possessed distinguishing feature of ellipsoidal morphology. The optical band gap of the as-prepared samples, Y1−xTbxNbO4, x = 0–1.0, decreased from 3.7 to 2.9 eV as the terbium concentration increased from x = 0 to 1.0. The photoluminescence spectra of the as-prepared nanocrystals containing terbium are responsible for the characteristic blue (490 nm) and green (545 nm) luminescence, associated with 5D4 → 7F6 and 5D4 → 7F5 transitions, respectively. The strongest emission bands in the green spectral domain corresponding to 5D4 → 7F5 transition of Tb3+ are located at 545 and 550 nm under excitation at 240 nm Xe lamp. By heat treatment at 1300 °C, the luminescence intensity of the as-prepared solid solution x = 0.10 that presented the highest photoluminescence intensity increased more than 8 times as high as that before heat treatment.

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