Structural Study of Europium Doped Gadolinium Polyphosphates LiGd(PO(3))(4) and Its Effect on Their Spectroscopic, Thermal, Magnetic, and Optical Properties

Alkali metal-rare earth polyphosphates LiGd((1-x))Eu(x)(PO(3))(4) (LGP:Eu(3+)) (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, β=90.082°, V= 894.214Å3, and Z=4. The similarity between R(F)=4.21% and R(B)=4.31% indicated that the realized refinement is reliable. The crystal structure consists of infinite zig-zag chains of (PO(4))(3-) 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(2-) and Eu(3+) (CTB), the energy transfer from Gd(3+) to Eu(3+), and the intrinsic 4f-4f transitions of Eu(3+) where the electronic transitions were also identified. Moreover, LGP:Eu(3+) 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 (5)D(0) to ground states (7)F(1) and (7)F(2), respectively.