Aeschynite-type fine crystals of YTiTaO 6 and Er 3+ -and Yb 3+ -co-doped YTiTaO 6 (YTiTaO 6 :Er 3+ /Yb 3+ ) were synthesized for the first time using hydrothermal method at 240°C. The effects of Yb 3+ and Er 3+ concentrations and heating temperature in air on their crystalline phases were investigated. The images of transmission electron microscope (TEM) and energy dispersive X-ray spectrometry (EDS) elemental mapping showed that their metal cations were dispersed homogeneously in the cube-like crystals in the range of 200300 nm. A single phase of aeschynite appeared in all of the as-prepared YTiTaO 6 and YTiTaO 6 :Er 3+ /Yb 3+ samples synthesized hydrothermally at 240°C and samples after heating at 1100 and 1200°C in air although YTiTaO 6 is known to possess euxenite-type structure. The lattice constants of the orthorhombic aeschynite phase decreased slightly according to the Vegard's law as the concentration of Yb 3+ was increased from y = 0 to 0.30 in the Er 0.10 Yb y Y 0.90¹y TiTaO 6 system. Under excitation at 270 nm the pure YTiTaO 6 showed light blue green and broadband photoluminescence centered at 520 nm. The aeschynite-to-euxenite phase transition occurred completely in the whole Yb 3+ concentration range, y = 00.30 in Er 0.10 Yb y Y 0.90¹y TiTaO 6 and pure YTiTaO 6 as a consequence of heating at 1400°C for 1 h in air.

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