Glycothermal synthesis and characterization of scheelite-type NaEuW ₂ O₈ nanophosphors

Scheelite-type NaEuW₂ O⁸ (NEW) nanophosphors were synthesized from a tungsten source and acetates of sodium and europium(III) in 1,4-butylene glycol by a glycothermal reaction. When dodecatungstophosphoric acid hexahydrate (DPA) was chosen as a tungsten source, a glycothermal reaction at temperatures ranging from 200 to 300°C produced crystalline NEW nanophosphors in a single phase. The tetrahedral PO₄ unit derived from DPA plays a significant role in the formation of crystalline NEW. The photoluminescence intensity due to the 4f-4f transitions of Eu3+ for the sample prepared at 200°C was over 80 times higher than that of the sample prepared at 300°C. The amount of organic species, determined by thermogravimetry, for the former was three times larger than that of the latter. We therefore conclude that the effect of surface passivation predominantly enhances the photoluminescence intensity of the scheelite-type NEW nanophosphor.