Sorption Studies of Eu³⁺ Ions Using YPO₄ and YPO₄:20% Ce Nanoparticles, Optical Properties, and in Conjunction with Instrumental Neutron Activation Analysis

The contamination of rare earth (RE) ions in an aqueous medium causes severe health hazards due to their toxicity. Hence, the removal of RE ions is necessary. In this work, we have used a concept of host-guest interaction which assists in the removal of RE ions by choosing the host as YPO₄ nanomaterial and the Eu³⁺ as foreign/guest ions. The YPO₄ host having two different phases like tetragonal (pure YPO₄) as well as hexagonal structure (20 at. % Ce³⁺-doped YPO₄) are used for comparative studies. A sorption study of Eu³⁺ was carried out with varying amounts of host (YPO₄ and/or YPO₄:20% Ce) at different pH values, i.e., 3 (acidic), 7 (neutral), and 12 (basic). The loading capacity of the host was studied via instrumental neutron activation analysis (INAA) and photoluminescence (PL) experiments. Here, the role of quenching is clearly explained in the PL. INAA is very sensitive to europium owing to its higher absorption cross-section (σ ∼ 9.2 × 10³ barn) and lower half-life (9.3 h). INAA using a short irradiation facility at PCF of the Dhruva reactor (1 min flux of neutrons at 5 × 10¹³ n/cm²/s) was effectively used to study the uptake of Eu³⁺ using its activation product ^152mEu (multi-γ-rays like 122, 344, and 842 keV). The order of uptake of Eu³⁺ ions over nanoparticles is acidic < neutral < basic medium. In the acidic medium (pH = 3), emission peaks at ∼590 and ∼615 nm could not be observed due to low sorption of Eu³⁺ over the host, whereas in the alkaline medium (pH = 12), their emission peaks are observed. It is interesting that at neutral pH, its uptake capacity is very good, and this has got a real case sample application for the removal of lanthanides.