Structural, optical and EPR studies of NaCe(PO 3 ) 4 metaphosphate doped with Cr 3+

The undoped and Cr3+-doped NaCe(PO3)4 metaphosphates were synthesized by the modified Pechini method and obtained as the crystalline powders. They were characterized by means of X-ray diffraction, vibrational and optical spectroscopy to clarify the structure and mechanism of Cr3+ emission in NaCe(PO3)4. This phosphor crystallizes in the monoclinic P121/n1 structure with an infinite (PO3)n chain. The Cr3+ ions can substitute the C1 symmetry site occupied by cerium ions. They can also occupy the tunnels formed in the anionic layer. Spectroscopic properties of the Cr3+ and Ce3+ ions were discussed in terms of structure of the studied crystalline powders. IR and Raman data confirm the predicted structure and indicate C1 site symmetry of the Cr3+ active ions. The Cr3+ ions appear in the distorted octahedral environment of the weak crystal field. Optical studies were confirmed by EPR results carried out in the temperature range of 4–293K. In addition, the magnetic measurements were performed up to 305K. The Cr3+ ions reveal negligible ferromagnetic interactions while the Ce3+ ions change their magnetic interactions from slightly antiferromagnetic to significantly ferromagnetic above 20K.