Novel tantalum phosphate Na13Sr2Ta2(PO4)9: synthesis, crystal structure, DFT calculations and Dy3+-activated fluorescence performance.

A new tantalum phosphate, tridecasodium distrontium ditantalum nonaphosphate, Na13Sr2Ta2(PO4)9, was prepared using the high-temperature flux method. The structure can be described as a three-dimensional open framework containing isolated [TaV2(PO4)9]17- units that are interlocked by Na and Sr ions. Band structure studies by the first-principles method revealed that Na13Sr2Ta2(PO4)9 is an insulator with an indirect band gap of 4.78 eV, which makes it suitable as a luminescent host matrix. A series of solid solutions, i.e. Na13Sr2-xTa2(PO4)9:xDy3+ (x = 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12 and 0.14), were prepared and their photoluminescence properties studied. Under 350 nm light excitation, these emit two typical emissions of the Dy3+ ion, i.e. the 4F9/2→6H15/2 transition centred at 476 nm and the 4F9/2→6H13/2 transition centred at 570 nm.