Crystal structure, vibrational spectra and optical properties of praseodymium cyclotriphosphate PrP3O9·3H2O

Single crystals of the trihydrated praseodymium cyclotriphosphate PrP3O9·3H2O were grown for the first time, using a classical method of aqueous chemistry and characterized by single crystal X-ray diffraction. PrP3O9·3H2O is isostructural with LnP3O9·3H2O (Ln = La, Ce and Nd). It crystallizes in the hexagonal system with space group P 6 ¯ ( C 3 h 1 ) , with lattice parameters: a = 6.7677(4) Å, b = 6.7677(4) Å, c = 6.0501(4) Å, V = 239.98(3) Å3, Z = 1 and Dx = 2.988 g cm−3. The crystal structure is resolved for the first time, with final R(F2) = 0.0175 and Rw(F2) = 0.0417 for 396 independent reflections ( F 0 2 ≥ 2 σ ( F 0 2 ) ) . The P3O93− cyclic anions have a plane configuration with C3h symmetry. The nearest neighbours of the rare earth ion are six oxygen atoms belonging to the P3O93− anions. Pr3+ ions occupy sites with C3h symmetry. The energies of the crystal vibrational modes are obtained from infrared (IR) and Raman spectra. Optical absorption measurements and emission spectra under selective excitation in the Pr3+ (4f2) 3PJ (J = 0, 1, 2) levels, at room and liquid-helium temperatures, are reported. The observed fluorescence originates mainly from 3P0 with a decay time on the order of 10 ns, regardless of temperature.