Hydrothermal synthesis of luminescent niobate thin rods

抄録

Luminescent columbite-type CaNb₂O₆ crystals undoped and doped with Eu³⁺ (CaNb₂O₆:Eu³⁺) and Tb³⁺ (CaNb₂O₆:Tb³⁺) have been synthesized at 240 °C using hydrothermal method from precursor solutions of inorganic salts. Microscopic examinations reveal that the morphology of the columbite crystals is like thin rods or needles (width: 0.1–0.3 µm, length 5–10 µm). The red, green, and blue light-emitting CaNb₂O₆-based materials have been prepared. Under the UV light excitation, the as-prepared CaNb₂O₆ presents a broad and blue photoluminescence (PL) peaked at 452 nm, originated from the niobate octahedral group [NbO₆]⁷⁻. The columbite-type CaNb₂O₆ with 12 mol % Eu³⁺ synthesized hydrothermally at 240 °C shows the strongest PL: weak orange and strong red light, attributed to the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions of Eu³⁺, respectively. The intensities of blue–green and green PL bands originated from the ⁵D₄→⁷F₆ and ⁵D₄→⁷F₅ transitions of Tb³⁺, respectively for the as-prepared CaNb₂O₆:Tb³⁺ reach the maximum at 10 mol % Tb³⁺, and their PL intensities have been improved by heating at 1000 °C in air.