JOURNAL of the Tunisian Chemical Society

A new alkali metal-rare earth polyphosphates NaGd_(1-x)Eu_x(PO₃)₄ (x= 0, 0.05, 0.10, 0.15) were prepared by solid state reaction. The obtained powders are identified by X-ray diffraction, Raman and Infrared spectroscopies. These polyphosphates crystallize in the monoclinic system with P 21/n space group and with cell parameters a= 7.174(1)Å, b= 13.033(2)Å, c= 9.781(1)Å, β= 90.65(2)°, V= 914.47(20)ų and Z= 4. The structure of NaGd(PO₃)₄ is both (PO₄)^3- zig-zag chains and an infinite chains formed by the alternate connection of GdO₈ polyhedra and LiO4 tetrahedra. The compound has good thermal stability to 920°C. Magnetic susceptibilities of single crystals were measured in the temperature range of 5-300 K. The compounds were paramagnetic, and obeyed the Curie-Weiss law in the entire temperature interval, without magnetic phase transitions. Optical properties of the Eu³⁺ doped NaGd(PO₃)₄ were investigated under λ_ex= 394 nm and λ_em= 591 nm at 300K. The excitation spectra have revealed from 200 to 350 nm the presence of Gd³⁺ 4f-5d interconfiguration transitions, Gd³⁺– O^2- and Eu³⁺– O^2- charge transfer states (CTS) in addition to intraconfiguration transitions of Gd³⁺ ions. Eu³⁺ doped phosphors can emit intense reddish orange light. The strongest two at 590 and 613 nm can be attributed to the transitions from excited state ⁵D₀ to ground states ⁷F₁ and ⁷F₂, respectively.

S. Hammami, N. Chniba Boudjada, A. Megriche

NGP polyphosphates, Infrared spectroscopy, magnetic properties, Optical materials, Raman spectroscopy

Pages 343-350