Efficient UV-emitting X-ray phosphors: octahedral Zr(PO4)6 luminescence centers in potassium hafnium–zirconium phosphates K2Hf1−xZrx(PO4)2 and KHf2(1−x)Zr2x(PO4)3

Potassium hafnium–zirconium phosphates, K₂Hf_1−xZr_x(PO₄)₂ and KHf_2(1−x)Zr_2x(PO₄)₃, are broad-band UV-emitting phosphors. At room temperature, they have emission peak maxima at approximately 322 and 305 nm, respectively, under 30 kV peak molybdenum X-ray excitation. Both phosphors demonstrate luminescence efficiencies that make them up to 60% as bright as commercially available CaWO₄ Hi-Plus. The solid-state and flux synthesis conditions, and X-ray excited UV luminescence of these two phosphors are discussed. Even though the two compounds have different atomic structures, they contain zirconium in the same active luminescence environment as that found in highly efficient UV-emitting BaHf_1−xZr_x(PO₄)₂. All the three materials have hafnium and zirconium in octahedral coordination via oxygen-atom corner sharing with six separate PO₄ tetrahedra. This octahedral Zr(PO₄)₆ moiety appears to be an important structural element for efficient X-ray excited luminescence, as are the edge-sharing octahedral TaO₆ chains for tantalate emission.