Structural, optical and EPR studies of NaCe(PO3)4 metaphosphate doped with Cr3+

- NaCe(PO3)4:Cr3+ crystalline powders were synthesized by the modified Pechini method.
- The optical and magnetic properties of the NaCe(PO3)4:Cr3+ crystalline powders were investigated.
- Cr3+ ions replacing Ce3+ ions in the unit cell are in the distorted octahedral environment.
- Cr3+ ions reveal ferromagnetic interactions, that strength depends on temperature.

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 4-293 K. In addition, the magnetic measurements were performed up to 305 K. The Cr3+ ions reveal negligible ferromagnetic interactions while the Ce3+ ions change their magnetic interactions from slightly antiferromagnetic to significantly ferromagnetic above 20 K.