Direct Formation of Luminescent Fine Crystals Based on (Y,Eu)TiNbO 6 Complete Solid Solution with High Crystallinity

Luminescent fine crystals of Y 1.00− x Eu x TiNbO 6 , x = 0–1.00 with high crystallinity were directly synthesized by mild hydrothermal method from weakly basic precursor solution mixtures of YCl 3 , EuCl 3 , TiOSO 4 , and NbCl 5 . Orthorhombic aeschynite‐type crystals in the range of 0.5–2.0 μm consisting of crystallites with 33–91 nm based on a complete solid solution in the YTiNbO 6 –EuTiNbO 6 system were hydrothermally formed at 240°C for 5 h. A single phase of as‐prepared aeschynite‐type structure was maintained in all the (Y,Eu)TiNbO 6 solid solution after heating at temperatures up to 1000°C for 1 h in air. In the range of composition x ≤ 0.6, the as‐prepared aeschynite‐type (Y,Eu)TiNbO 6 solid solutions transformed to a single phase of euxenite structure after heat treatment at temperatures higher than 1100°C–1200°C. The as‐prepared (Y,Eu)TiNbO 6 fine crystals in the range of composition x = 0.75–0.90 showed the strongest luminescence in the red spectral region: strong red ( 5 D 0 → 7 F 2 transition of Eu 3+ ) and weak orange light ( 5 D 0 → 7 F 1 ) line spectra among the as‐prepared and heat‐treated samples. Another wet chemical synthesis route confirmed the advantage in directly synthesizing the (Y,Eu)TiNbO 6 crystals through this hydrothermal method because heating at 1200°C for 1 h in air was necessary for obtaining crystalline (Y,Eu)TiNbO 6 with sufficient luminescence intensity in a composition Y 0.70 Eu 0.30 TiNbO 6 from amorphous powders that were formed via co‐precipitation method.