Synthesis of blue-luminescent CaNb₂O₆ by using a biphasic liquid method at low temperatures

We investigated a novel simple method to synthesize CaNb₂O ₆ from precursors formed in immiscible liquid-liquid biphasic systems. Niobium pentaethoxide and calcium acetate monohydrate were used as starting materials, which were dissolved separately in hexane and water, respectively. After putting the hexane solution on the aqueous solution, they started to react at the interface of the two liquid phases and then a mixture of calcium acetate and amorphous niobate gels was precipitated in the aqueous solution at room temperature. The precipitates could be transformed to CaNb ₂O₆ by heating at 700°C for 30min. The morphology of the CaNb₂O₆ sample was characterized as rough and dimpled spheres 400-500nm in size. The sample exhibited a blue emission upon excitation with ultraviolet light. A comparative study using a one-phase liquid method or a solid-state reaction method has strongly suggested that the biphasic liquid method is advantageous for obtaining highly luminescent CaNb₂O ₆ at the lower processing temperatures.