Mild Hydrothermal Crystal Growth of Two Luminescing Uranyl Phosphates Exhibiting an Autunite-Type Sheet Structure

Two new layered uranyl phosphate compounds, K(UO2)PO4(H2O)3 and Na(UO2)PO4(H2O)1.52, crystallizing in an autunite-type sheet structure, were successfully synthesized as both single-crystals and polycrystalline powders under mild hydrothermal conditions. The compound K(UO2)PO4(H2O)3 crystallizes in the tetragonal crystal system with the space group P4/ncc, exhibiting lattice parameters of a = b = 6.99320(7) Å and c = 17.8389(3) Å. Similarly, Na(UO2)PO4(H2O)1.52 also crystallizes in the tetragonal crystal system, however, in the space group P4/nmm and exhibits lattice parameters of a = b = 6.9787 Å and c = 8.6303(17) Å. Both compounds adopt layered structures, a characteristic feature of uranyl phosphates, and exhibit intense green fluorescence typical for uranyl-containing materials. The infrared spectroscopy, photoluminescence, and scintillation properties of these compounds were investigated.