Structural Study of Europium Doped Gadolinium Polyphosphates LiGd(PO) and Its Effect on Their Spectroscopic, Thermal, Magnetic, and Optical Properties.

Alkali metal-rare earth polyphosphates LiGdEu(PO) (LGP:Eu) (where x= 0, 0.02 and 0.04) were synthesized by solid-state reaction. The Rietveld refinement showed the following cell parameters: I 2/a space group, a=9.635(3) Å, b=7.035(3) Å, c=13.191(3) Å, =90.082°, V= 894.214Å3, and Z=4. The similarity between R=4.21% and R=4.31% indicated that the realized refinement is reliable. The crystal structure consists of infinite zig-zag chains of (PO) tetrahedra, linked by bridging oxygen. The acyclic structure of polyphosphates is confirmed by infrared and Raman (IR) spectroscopies. A good thermal stability up to 940°C and paramagnetic behavior of these compounds were also proved by thermal analyses and magnetic susceptibility measurements, respectively. Excitation spectra revealed the charge transfer phenomenon between O and Eu (CTB), the energy transfer from Gd to Eu, and the intrinsic 4f-4f transitions of Eu where the electronic transitions were also identified. Moreover, LGP:Eu can emit intense reddish orange light under excitation at 394 nm. The strongest tow at 578 and 601 nm can be attributed to the transitions from excited state D to ground states F and F, respectively.