Solid State Synthesis and Material Characterizations of Heat-Sensitive Nanocrystalline Sm3+ Doped NaLi2PO4 for Thermoluminescent Dosimetric Investigations

Abstract

Nanocrystalline NaLi₂PO₄:Sm³⁺ (0.1 mol %) powder phosphor material was synthesized via solid-state reaction method in air atmosphere. The material was characterized by XRD, FESEM, EDS, FTIR, Raman and UV-Visible spectroscopy. Furthermore, the thermoluminescence (TL) dosimetric response of the nanocrystalline powder samples was also examined. XRD analysis revealed the highly crystalline orthorhombic structure of the primary phase with an average crystallite size of 31 nm, alongside the presence of an additional secondary phase indicative of a distinct material. FESEM revealed significant agglomeration, containing non-uniform, irregular, self-oriented clusters having average particle size of 0.37 μm. EDS verified the substantial weight percentages of Samarium in the NaLi₂PO₄:Sm³⁺ composition. FTIR spectroscopy provided prominent absorption bands at 1060 and 1019 cm⁻¹ corresponding to the stretching vibrations of the (PO₄)³⁻ group. Raman spectroscopy further corroborated the presence of distinct vibrational modes of the (PO₄)³⁻ group, associated with the nanoparticle surface. UV-Visible spectroscopy revealed characteristic charge transfer transition of PO and multiple sharp f–f transitions, including a prominent absorption band at 401 nm attributed to the ⁶H_5/2 →⁶P_3/2 transition of Sm³⁺ ions. The influence of various annealing conditions on the TL response of NaLi₂PO₄:Sm³⁺ was investigated. Samples were irradiated at various doses from ⁶⁰Co γ-source. Phosphor showed a prominent TL peak at 207 °C. TL glow curve of this phosphor, irradiated by ⁶⁰Co γ-rays at 40 Gy dose, measured at heating rate of 10 K/s has 8 deconvoluted glow peaks leading to highly dense trap at 478 K. Moreover, material showed the linear dose response against gamma radiations ranging 0–40 Gy. Based on these results, NaLi₂PO₄:Sm³⁺ (0.1 mol %) is a promising material and has good potential for TL dosimetry.