Electronic absorption and vibrational IR and Raman studies of binary phosphate β-K4Ce2P4O15

The binary phosphate K4Ce2P4O15 was prepared in the polycrystalline state in the solid state reaction of cerium oxide and potassium phosphate KPO3. The phosphate fragment of this compound appears in the form of two PO43- and one P2O74- anions occupying the sites of low symmetry. Electronic absorption, emission as well as infrared and Raman spectroscopic methods have been applied to characterise the properties and structure of the compound studied. Its electronic spectra agree with the Ce3+ ion spectroscopic characteristics. The 2F5/2→2F7/2 transition appears in the typical for this ion region: about 2000 cm-1. The multiplet structure of the spectrum suggests the existence of at least two crystallographic different sites of this ion in the unit cell. The absorption bands in the range 25000-45000 cm-1 have been assigned to the 4f1→5d1 transitions of the cerium ion and CT transition of the phosphate ligands. The vibrational spectra were discussed on the basis of correlation diagrams and factor group analysis. The radiation-less mechanism of the return from the excited state to the ground state via CT states in the system studied is proposed