The development of efficient and robust scintillator materials is crucial for advancing radiation detection and imaging technologies. Existing scintillators often suffer from limitations such as low sensitivity, poor stability, or complex fabrication processes. This research aims to address these challenges by developing a novel class of scintillators based on copper(I)-iodide clusters. Copper(I) iodide-based materials have garnered attention due to their strong X-ray stopping power and exceptional X-ray conversion efficiency stemming from their photoluminescence and semiconducting properties. However, challenges remain in achieving uniform morphology and improving their resistance to moisture. This study focuses on synthesizing high-performance monodisperse microcube scintillators with enhanced stability and exploring their applications in X-ray imaging. The successful development of such materials could significantly impact various fields, including medical imaging, security screening, and nuclear physics research. The research question revolves around the optimization of synthesis to obtain highly efficient and stable copper(I)-iodide based scintillators.

The literature review highlights the existing challenges in scintillator materials, emphasizing the need for improved X-ray stopping power, conversion efficiency, and environmental stability. Previous studies have explored various materials, including perovskites and other metal halide compounds. However, these often suffer from limitations like sensitivity to moisture and limited tunability. The authors cite previous studies supporting the potential of copper(I)-iodide based materials, which offer high X-ray stopping power due to the presence of heavy elements like copper and iodine. Structure engineering is highlighted as a key approach to improve the lattice stability and water resistance of these materials. The existing literature sets the stage for the presented research, positioning the newly developed copper iodide-(1-propyl-1,4-diazabicyclo[2.2.2]octan-1-ium)₂ microcubes as a potential solution to overcome the shortcomings of currently available scintillators.

The synthesis of Cu₄I₆(pr-ted)₂ microcubes involved a hot-injection method, where 1-propyl-1,4-diazabicyclo[2.2.2]octan-1-ium (pr-ted) was injected into a mixture of KI-saturated CuI and polyvinylpyrrolidone (PVP) at 70 °C. The reaction was quenched using a water-ice bath, and the resulting product was annealed at 200 °C for 1.5 h under a nitrogen atmosphere. The crystal structure was confirmed through X-ray diffraction (XRD), while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the morphology and size distribution of the microcubes. Elemental mapping and X-ray photoelectron spectroscopy (XPS) verified the elemental composition. Density functional theory (DFT) calculations were employed to investigate the electronic band structure, band gap, and optical properties. Photoluminescence (PL) spectroscopy was used to study the optical properties, including photoluminescence quantum yield (PLQY) and temperature-dependent emission. Radioluminescence measurements were conducted to evaluate the X-ray detection efficiency and response. The stability of the microcubes was evaluated through water resistance tests and X-ray irradiation experiments. The performance was compared against other known scintillators.

The synthesized Cu₄I₆(pr-ted)₂ microcubes exhibited a uniform cubic morphology with an average size of 2.2 µm. DFT calculations revealed a bandgap of 2.93 eV, with the conduction band primarily composed of Cu 3d and I 5p orbitals. The microcubes displayed strong green radioluminescence at 535 nm, identical to phosphorescence under 365 nm excitation. Annealing significantly improved the PLQY from 40.7% to 97.1%. The microcubes showed remarkable water resistance, unlike other comparable materials such as CsPbBr₃ and Cs₃Cu₂I₅. The effective atomic number of Cu₄I₆(pr-ted)₂ (45.6) is comparable to other scintillators. Radioluminescence testing demonstrated that Cu₄I₆(pr-ted)₂ microcubes exhibit superior performance compared to several commercially available scintillators (YAIO₃:Ce, Bi₄Ge₃O₁₂, PbWO₄) and other reported materials (Cs₃Cu₂I₅, CsCu₂I₃, CsPbBr₃). The X-ray detection limit was determined to be 22 nGy_air s⁻¹. The microcubes also showed excellent resistance to continuous and repeated X-ray irradiation, maintaining their radioluminescence intensity over time.

The superior performance of the Cu₄I₆(pr-ted)₂ microcubes can be attributed to a combination of their structural properties and intrinsic optical characteristics. The high atomic number elements (Cu and I) contribute to strong X-ray stopping power, while the efficient energy migration from the host to the emission centers and strong emission from triplet cluster-centered (CC) excited states lead to high X-ray conversion efficiency. The uniform cubic morphology and structural robustness contribute to the high performance and water resistance. The results suggest that the coordination bonding between Cu and I, and between Cu and the organic ligand, contributes to the improved water resistance compared to ionic scintillators. The exceptional performance of these microcubes surpasses that of several commercially available and reported scintillators, validating their potential as advanced materials for X-ray detection and imaging. The findings open new avenues for the development of efficient and robust scintillators.

This study successfully synthesized high-performance monodisperse Cu₄I₆(pr-ted)₂ microcube scintillators with excellent X-ray detection capabilities and remarkable water resistance. Their superior performance compared to existing scintillators positions them as promising candidates for diverse applications in radiation detection and imaging. Future research could focus on exploring other organic ligands to further optimize the properties of these scintillators and investigate their scalability for large-scale production.

The study primarily focuses on the characterization and performance evaluation of the synthesized microcubes. Further investigation is required to fully explore their long-term stability under various environmental conditions and potential degradation mechanisms. The impact of particle size distribution on the overall performance could be explored further. Finally, a comprehensive in vivo study to validate the effectiveness of these scintillators in real-world applications is necessary.