Thermoluminescence in Eu doped NaLi2PO4TLD nanophosphor: Effect of particle size on TL characteristics

Highlights: • NaLi₂PO₄:Eu microcrystalline and nanocrystalline materials prepared by ball milling. • Characterization of materials by XRD show stress/strain developed. • TL intensity firstly increases up to particle size ~90 μm and decreases further with particle size. • Widening of the dose response is clearly seen in case of the nanophosphors. • NaLi₂PO₄:Eu nanophosphor found to be a good TLD for estimation of very high doses of γ-radiation. We report the thermoluminescence of Eu-doped NaLi₂PO₄ synthesized by solid state diffusion method. Formation of the material was confirmed by powder X-ray diffraction (PXRD) technique. Broadening of the PXRD peaks and field emission scanning microscope (FESEM) images were used for determining its particle size(s). Thermoluminescence (TL) characteristics were studied to see the effect of particle size after irradiating with $\gamma$ -rays from ⁶⁰Co source for wide-range (10 Gy-100 kGy) of doses. It was observed that not only TL sensitivity but also glow curve structure depends on particle size of the material. Glow curves were further deconvoluted using computerized glow curve deconvolution (CGCD) technique (after confirming the number of peaks using T_m-T_stop method) to study trapping parameters. TL glow curves mainly consist of four peaks appearing in the temperature ranges of 378–385, 426–435, 447–458 and 497–506 K. The shifts in the TL glow peak temperatures and the changes in glow curve structures can be attributed to the reorganization of local impurity levels (electron traps/luminescence centers) on widening of the band gap with reducing particle size. There can also be the effect of stress on glow curves developed due to crushing. Widening of the dose response with reducing particle size, easy method of synthesis, high sensitivity, low fading, good chemical stability, etc. make this TLD nanophosphor a good candidate for radiation dosimetry using TL.