Hydrothermal synthesis and photoluminescence properties of rare-earth niobate and tantalate nanophosphors

Rare-earth niobate and tantalate materials are of considerable interest for use as phosphors, photocatalysts and ionic conductors. We successfully synthesized Ln(3)MO(7) (Ln = Y, Ce, Er, Ho, Tm, Yb and Lu, M = Ta, Nb) nanophosphors by a hydrothermal method using the water-soluble Lindqvist ion polyoxometalates [HNb6O19](7-) and [Ta6O19](8-) as Nb and Ta sources. The Pawley refinements of these nanophosphors revealed that the Lu3TaO7 and Lu3NbO7 nanophosphors could be indexed in the cubic system with the space group Fm (3) over barm, and that Y3TaO7 crystallizes in orthorhombic symmetry with the space group of C2221. These three solid compounds are nanoparticles with average particle sizes of 7.5, 5.9 and 4.0 nm for Lu3TaO7, Lu3NbO7 and Y3TaO7, respectively. The photoluminescence properties of Eu3+ doped Lu3TaO7, Lu3NbO7 and Y3TaO7 were studied, and Eu3+/Sr2+ co-doped Ln(3)MO(7) (M = Ta, Nb) has an enhanced emission intensity compared to that of Ln(3)MO(7):Eu3+ (M = Ta, Nb).