Synthesis, characterization and luminescence study of Na⁺ and Sm³⁺ substituted fluorapatite matrix

Molten salt reactor wastes are not suitable to immobilize in borosilicate glass matrixes due to the fact that boron and silicon containing glasses are highly unstable in presence of fluoride ion sources, which lead to the formation of highly stable compounds like boron tri-fluoride (BF₃) and silicon tetra fluoride (SiF₄). The presence of highly reactive fluorides of the fission products and spent uranium can make the borosilicate glasses less durable which results in contamination of high amount of radiation in the surrounding environment. Thus an alternative to glass matrix for radioactive waste immobilization is required on an urgent base before the startup of next generation molten salt reactors. Fluorapatite with the chemical formula Ca₁₀(PO₄)₆F₂, is the most abundant and stable naturally occurring fluoride based apatite mineral due to highly stable Ca-F bonds and it can retains significant actinides and fission products. So the fission products incorporated matrix should be artificially developed and a detail study on their structural and physical properties is very much needed before certifying them as an alternate candidate for the radioactive waste forms for generated nuclear waste from molten salt reactor. It is well known that the luminescence properties of lanthanides (such as Eu³⁺ and Sm³⁺) are widely used as photoluminescence probe for structural studies and cationic site occupancy in the matrix besides their application in solid state lighting and bioimaging etc. The phosphate based lanthanides are highly stable and can be used as cost effective luminescent material for various applications. In present work our main focus is on synthesis and characterization of Na⁺ and Sm³⁺ doped Fluorapatite compound and the distribution of dopant ion using Photoluminescence spectroscopy. The chosen monovalent and trivalent cations are Na⁺ and Sm³⁺ respectively. Here Sm³⁺ is used as surrogates of Np³⁺ ions in the high level waste. Thus this study has significance in view of its application in the development of ceramic based nuclear waste immobilization technology