High-Sensitivity and Wide-Linear-Range Thermoluminescence Dosimeter LiMgPO4:Tm,Tb,B for Detecting High-Dose Radiation

Manipulation of Shallow-Trap States in Halide Double Perovskite Enables Real-Time Radiation Dosimetry

Storage phosphors displaying defect emissions are indispensable in technologically advanced radiation dosimeters. The current dosimeter is limited to the passive detection mode, where ionizing radiation-induced deep-trap defects must be activated by external stimulation such as light or heat. Herein, we designed a new type of shallow-trap storage phosphor by controlling the dopant amounts of Ag+ and Bi3+ in the host lattice of Cs2NaInCl6. A distinct phenomenon of X-ray-induced emission (XIE) is observed for the first time in an intrinsically nonemissive perovskite. The intensity of XIE exhibits a quantitative relationship with the accumulated dose, enabling a real-time radiation dosimeter. Thermoluminescence and in situ X-ray photoelectron spectroscopy verify that the emission originates from the radiative recombination of electrons and holes associated with X-ray-induced traps. Theoretical calculations reveal the evolution process of Cl-Cl dimers serving as hole trap states. Analysis of temperature-dependent radioluminescence spectra provides evidence that the intrinsic electron-phonon interaction in 0.005 Ag+@ Cs2NaInCl6 is significantly reduced under X-ray irradiation. Moreover, 0.025 Bi3+@ Cs2NaInCl6 shows an elevated sensitivity to the accumulated dose with a broad response range from 0.08 to 45.05 Gy. This work discloses defect manipulation in halide double perovskites, giving rise to distinct shallow-trap storage phosphors that bridge traditional deep-trap storage phosphors and scintillators and enabling a brand-new type of material for real-time radiation dosimetry.

Exploring the role of vacancy defects in the optical properties of LiMgPO4

Linearity in dose response up to very high radiation doses and sufficient sensitivity to even low radiation doses are extremely important for the measurement of radiation dose in the field of radiation technology, ranging from medical to industrial applications. Olivine type LiMgPO4 has been shown immense interest as a phosphor material in the fields of thermoluminescence and optically stimulated luminescence dosimetry. In the present study, we have explored the role of different vacancy defects in the optical properties of LiMgPO4 aiming at enhancing its sensitivity for the measurement of radiation dose. For this purpose, we have systematically investigated the electronic structure of LiMgPO4 in the absence and presence of various vacancy defects using density functional theory as a tool. The present study considers all possible vacancy defects including neutral, charged and mixed lattice vacancy defects in LiMgPO4. To find the most energetically favourable vacancy defect, we have compared the defect formation energy of all the vacancy defects. We have also calculated vacancy formation energy in different chemical environments to investigate how the formation of different types of vacancy defect can be controlled by tuning the chemical environment. Finally, the origin of the different optical properties of LiMgPO4 has been explained by using a possible mechanism based on our detailed electronic structure calculations. Thus, the present study is believed to provide valuable insight for the development of materials with improved features for the measurement of radiation dose.

Unusual intrinsic thermoluminescence in LiMgPO4:Er

Enhancement of stimulated luminescence in LiMgPO₄ due to energy transfer from Er³⁺ to the optical matrix.

Photoenergy Conversion Behaviors of Photoluminescence and Photocatalysis in Silver-Coated LiBaPO4:Eu2

LiBaPO₄:Eu²⁺ phosphor and Ag-coated LiBaPO₄:Eu²⁺ composites (Ag/LiBaPO₄:Eu²⁺) were prepared via solid-state reaction and traditional photoreduction methods, respectively. The samples were characterized via XRD, SEM, and UV-vis optical absorption spectroscopy. Two photoenergy conversion processes, namely, photocatalysis and photoluminescence, were investigated in detail. In comparison with as-prepared LiBaPO₄:Eu²⁺ phosphor, Ag-modified composites exhibited the enhanced photocatalytic effects together with the quenched Eu²⁺ luminescence. A Schottky barrier was created on the interface between Ag nanoparticles and LiBaPO₄ host, thereby greatly delaying the recombination between the light-induced holes and electrons. A photoenergy conversion mechanism was suggested and discussed on the basis of the experiments. The Eu²⁺ ion luminescence centers directly participated in the photodegradation with the meditation of Ag nanoparticles on the surface. With the increase of the Ag coating level on the surfaces, some emission peaks corresponding to ⁵D₀ → ⁷F_0,1,2,3,4 transitions of Eu³⁺ ions were detected. Eu²⁺/Eu³⁺ couples also play an important role in improving photocatalysis. LiBaPO₄:Eu²⁺ phosphor is a good candidate for the investigation of multimodal photoenergies of photoluminescence and photocatalysis.