Effect of annealing and impurity concentration on the TL characteristics of nanocrystalline Mn-doped CaF2

• Nanocrystalline material CaF2:Mn is prepared by simple coprecipitation method.
• The material is studied by XRD, TEM, ESR, TL and PL techniques.
• High impurity concentrations give rise to clusters causing material instability.
• Changes in ESR and PL and glow curve structures are studied and explained.
• Better characteristics than the bulk make the nanophosphor useful for dosimetry.

Nanocrystalline samples of Mn-doped CaF2 were synthesized by chemical coprecipitation method. The impurity concentration was varied in the range of 0.5–4.0 mol%. The structure of the synthesized material was confirmed using powder XRD analysis. TEM images of the nanoparticles show their size occurring mostly in the range of 35–40 nm, with clusters of some impurity phases formed on annealing of the material at higher temperatures. Detailed studies on TL showed that the structures of glow curves depend on Mn concentrations and annealing temperatures. Optimization of the concentration and annealing temperature showed that the sample (doped with 3.0 mol% and annealed at 673 K) has almost a single dosimetric glow peak appearing at around 492 K. EPR and PL spectra were further studied to understand the reasons for changes in the glow curve structures. All detailed studies on TL, PL and EPR showed that the changes in glow curve structures are caused not only by the stress connected with the difference in ionic radii of host Ca2+ and the guest impurity Mn3+/Mn2+, but are also governed by other reasons, like diffusion of atmospheric oxygen and formation of impurity aggregates, such as, MnO2, Mn3O4, etc. This is true not only for nanocrystalline CaF2:Mn but could also be so for the bulk CaF2:Mn (TLD-400) and would thus help in understanding complex glow curve structure, high fading and the loss of reusability on annealing beyond 673 K.