Synthesis and characterization of K2Pr2O(BO3)2: structural, spectroscopic and thermogravimetric investigations of a novel potassium praseodymium oxoborate structure-type

Abstract

Single crystal and polycrystalline powder samples of a new potassium praseodymium oxoborate K2Pr2O(BO3)2 were prepared by high-temperature solid-state methods. The crystal structure obtained from single-crystal X-ray diffraction data was confirmed by powder X-ray data Rietveld refinement (P21/c, a = 1135.00(3) pm, b = 660.64(2) pm, c = 1072.03(3) pm, β = 117.128(2)°, V = 715.41(3) × 106 pm3). The bond-valence sum of the central cation for KO6/7, PrO9 and BO3 coordination lies close to the respective empirical value. Both Fourier-transform infrared and Raman spectroscopy demonstrated the vibrational features of the isolated BO3 planar group. The diffuse UV/Vis reflectance spectra showed fundamental absorption edge at 4.49(1) eV obtained from the combined approach using Tauc and derivation of absorption spectrum fitting methods. The greenish color of the sample was identified originating from 4f–4f-electron transitions. The thermal stability was investigated by using simultaneous thermogravimetric analysis and differential scanning calorimetry. The decomposed products Pr26O27(BO3)8 (90(2) wt%) and Pr6O11 (10(2) wt%) were confirmed by powder X-ray diffraction data analysis, complementary to the weight-loss during the heating process. Since Pr3+ cation is known to show interesting photoluminescence property, this novel compound may be a prospective candidate as phosphor.