Multifunctional Ca₁₀(PO₄)₆F₂ as a host for radioactive waste immobilization: Am³⁺/Eu³⁺ ions distribution, phosphor...

Na⁺₂Eu³⁺₂:Ca₆(PO₄)₆F₂ is explored as a potential host for radioactive waste immobilization. Since Eu³⁺ ion is a surrogate of highly radioactive Am³⁺ ion, the photoluminescence (PL) characteristics of Eu³⁺ ion helped to investigate the possible distribution of hazardous and radioactive Am³⁺ ion among the two lattice sites in the matrix. It was observed that Am³⁺ will prefer to occupy the Ca2-site lattice which has a direct linkage to F atom. From DFT calculation we have found that both Eu³⁺ and Am³⁺ ions are following similar trend of distribution into the Ca2-site compared to Ca1-site which has no F atom linkage. The radiation stability of the compound was also investigated by PL study after irradiating it with a ⁶⁰Co gamma source with different doses starting from 2 kGy to as high as 1000 kGy. It was observed that radiation induced changes were more surrounding the Ca1-site than in Ca2-site.Considering all the experimental and theoretical observations it is concluded that from radioactive waste immobilization point of view it is more preferable to dope the Am³⁺ ion into the Ca2 site. The Eu³⁺ doped compound was also found to be red color emitting phosphor materials with color purity of 95.24%.