Perovskite Scintillators for Improved X-ray Detection and Imaging

Halide perovskites (HPs) recently have emerged as one class of competitive scintillators for X-ray detection and imaging owing to its high quantum efficiency, short decay time, superior X-ray absorption capacity, low cost, and ease of crystal growth. The tunable structure and versatile chemical compositions of halide perovskites provide distinguishable advantages over traditional inorganic scintillators for optimizing scintillation performance. Since the first observation of the scintillation phenomenon in HPs, substantial efforts have been devoted to expanding the inventory of HP scintillators and regulating material properties. Understanding the relationship between the structure and scintillation properties of HP scintillators is essential for developing materials with improved X-ray detection and imaging capacities. This review summarizes strategies for improving the light yield of HP scintillators and provides a roadmap for improving the X-ray imaging performance. Additionally, methods for controlling the light propagation direction in HP scintillators are highlighted for improving X-ray imaging resolution. Finally, we highlight the current challenge in HP scintillators and provide a perspective on the future development of this emerging scintillator.

Highly Effective Hybrid Copper(I) Iodide Cluster Emitter with Negative Thermal Quenched Phosphorescence for X-Ray Imaging

The low efficiency triplet emission of hybrid copper(I) iodide clusters is a critical obstacle to their further practical optoelectronic application. Herein, we present an efficient hybrid copper(I) iodide cluster emitter (DBA)₄ Cu₄ I₄ , where the cooperation of excited state structure reorganization and the metallophilicity interaction enables ultra-bright triplet yellow-orange emission with a photoluminescence quantum yield over 94.9 %, and the phonon-assisted de-trapping process of exciton induces the negative thermal quenching effect at 80-300 K. We also investigate the potential of this emitter for X-ray imaging. The (DBA)₄ Cu₄ I₄ wafer demonstrates a light yield higher than 10⁴  photons MeV^-1 and a high spatial resolution of ≈5.0 lp mm^-1 , showing great potential in practical X-ray imaging applications. Our new copper(I) iodide cluster emitter can serve as a model for investigating the thermodynamic mechanism of photoluminescence in hybrid copper(I) halide phosphorescence materials.

Pseudo-2D Layered Organic-Inorganic Manganese Bromide with a Near-Unity Photoluminescence Quantum Yield for White Light-Emitting Diode and X-Ray Scintillator

Eco-friendly lead-free organic-inorganic manganese halides (OIMHs) have attracted considerable attention in various optoelectronic applications because of their superior optical properties and flexible solution processibility. Herein, we report a novel pseudo-2D layered OIMH (MTP)2 MnBr4 (MTP: methyltriphenylphosphonium), which exhibits intense green emission under UV/blue or X-ray excitation, with a near-unity photoluminescence quantum yield, high resistance to thermal quenching (I150 °C =84.1 %) and good photochemical stability. These features enable (MTP)2 MnBr4 as an efficient green phosphor for blue-converted white light-emitting diodes, demonstrating a commercial-level luminous efficiency of 101 lm W-1 and a wide color gamut of 116 % NTSC. Moreover, these (MTP)2 MnBr4 crystals showcase outstanding X-ray scintillation properties, delivering a light yield of 67000 photon MeV-1 , a detection limit of 82.4 nGy s-1 , and a competitive spatial resolution of 6.2 lp mm-1 for X-ray imaging. This work presents a new avenue for the exploration of eco-friendly luminescent OIMHs towards multifunctional light-emitting applications.

Wide-Range Color-Tunable Organic Scintillators for X-Ray Imaging Through Host-Guest Doping

With the increasing demands of X-ray detection and medical diagnosis, organic scintillators with intense and tunable X-ray excited emission have been becoming important. To guarantee the X-ray absorption, heavy atoms were widely added in reported organic scintillators, which led to emission quenching. In this work, we propose a new strategy to realize organic scintillators through the host-guest doping strategy. Then the X-ray absorption centers (host) and emission centers (guest) are separated. Under X-ray excitation, these materials displayed intense and readily tunable emissions ranging from green (520 nm) to near infrared (NIR) regions (682 nm). Besides, the relationship between the X-ray absorption and spatial arrangement of the heavy atoms in the host matrix was also revealed. The potential application of these wide-range color tunable organic host-guest scintillators in X-ray imaging were demonstrated. This work provides a new feasible strategy for constructing high-performance organic scintillators with tunable luminescence properties.

Dimensional and Optoelectronic Tuning of Lead-free Perovskite Cs3 Bi2 I9-n Brn Single Crystals for Enhanced Hard X-ray Detection

Inorganic Bi-based perovskites have shown great potential in X-ray detection for their large absorption to X-rays, diverse low-dimensional structures, and eco-friendliness without toxic metals. However, they suffer from poor carrier transport properties compared to Pb-based perovskites. Here, we propose a mixed-halogen strategy to tune the structural dimensions and optoelectronic properties of Cs3 Bi2 I9-n Brn (0≤n≤9). Ten centimeter-sized single crystals are successfully grown by the Bridgman technique. Upon doping bromine to zero-dimensional Cs3 Bi2 I9 , the crystal transforms into a two-dimensional structure as the bromine content reaches Cs3 Bi2 I8 Br. Correspondingly, the optoelectronic properties are adjusted. Among these crystals, Cs3 Bi2 I8 Br exhibits negligible ion migration, moderate resistivity, and the best carrier transport capability. The sensitivities in 100 keV hard X-ray detection are 1.33×104 and 1.74×104  μC Gyair -1  cm-2 at room temperature and 75 °C, respectively, which are the highest among all reported bismuth perovskites. Moreover, the lowest detection limit of 28.6 nGyair  s-1 and ultralow dark current drift of 9.12×10-9  nA cm-1  s-1  V-1 are obtained owing to the high ionic activation energy. Our work demonstrates that Br incorporation is an effective strategy to enhance the X-ray detection performance by tuning the dimensional and optoelectronic properties.

Analysis of Volume Overestimation Artifacts in the Breast Outline Segmentation in Tomosynthesis

In digital breast tomosynthesis (DBT), the reconstruction is calculated from x-ray projection images acquired over a small range of angles. One step in the reconstruction process is to identify the pixels that fall outside the shadow of the breast, to segment the breast from the background (air). In each projection, rays are back-projected from these pixels to the focal spot. All voxels along these rays are identified as air. By combining these results over all projections, a breast outline can be determined for the reconstruction. This paper quantifies the accuracy of this breast segmentation strategy in DBT. In this study, a physical phantom modeling a breast under compression was analyzed with a prototype next-generation tomosynthesis (NGT) system described in previous work. Multiple wires were wrapped around the phantom. Since the wires are thin and high contrast, their exact location can be determined from the reconstruction. Breast parenchyma was portrayed outside the outline defined by the wires. Specifically, the size of the phantom was overestimated along the posteroanterior (PA) direction; i.e., perpendicular to the plane of conventional source motion. To analyze how the acquisition geometry affects the accuracy of the breast outline segmentation, a computational phantom was also simulated. The simulation identified two ways to improve the segmentation accuracy; either by increasing the angular range of source motion laterally or by increasing the range in the PA direction. The latter approach is a unique feature of the NGT design; the advantage of this approach was validated with our prototype system.

Personalization of X-Ray Tube Motion in Digital Breast Tomosynthesis Using Virtual Defrise Phantoms

In digital breast tomosynthesis (DBT), projection images are acquired as the x-ray tube rotates in the plane of the chest wall. We constructed a prototype next-generation tomosynthesis (NGT) system that has an additional component of tube motion in the perpendicular direction (i.e., posteroanterior motion). Our previous work demonstrated the advantages of the NGT system using the Defrise phantom. The reconstruction shows higher contrast and fewer blurring artifacts. To expand upon that work, this paper analyzes how image quality can be further improved by customizing the motion path of the x-ray tube based on the object being imaged. In simulations, phantoms are created with realistic 3D breast outlines based on an established model of the breast under compression. The phantoms are given an internal structure similar to a Defrise phantom. Two tissue types (fibroglandular and adipose) are arranged in a square-wave pattern. The reconstruction is analyzed as a binary classification task using thresholding to segment the two tissue types. At various thresholds, the classification of each voxel in the reconstruction is compared against the phantom, and receiver operating characteristic (ROC) curves are calculated. It is shown that the area under the ROC curve (AUC) is dependent on the x-ray tube trajectory. The trajectory that maximizes AUC differs between phantoms. In conclusion, this paper demonstrates that the acquisition geometry in DBT should be personalized to the object being imaged in order to optimize the image quality.

Thermally Activated Delayed Fluorescence (TADF)-active Coinage-metal Sulfide Clusters for High-resolution X-ray Imaging

The study of facile-synthesis and low-cost X-ray scintillators with high light yield, low detection limit and high X-ray imaging resolution plays a vital role in medical and industrial imaging fields. However, the optimal balance between X-ray absorption, decay lifetime and excitonic utilization efficiency of scintillators to achieve high-resolution imaging is extremely difficult due to the inherent contradiction. Here two thermally activated delayed fluorescence (TADF)-actived coinage-metal clusters M6 S6 L6 (M=Ag or Cu) were synthesized by simple solvothermal reaction, where the cooperation of heavy atom-rich character and TADF mechanism supports strong X-ray absorption and rapid luminescent collection of excitons. Excitingly, Ag6 S6 L6 (SC-Ag) displays a high photoluminescence quantum yield of 91.6 % and scintillating light yield of 17420 photons MeV-1 , as well as a low detection limit of 208.65 nGy s-1 that is 26 times lower than the medical standard (5.5 μGy s-1 ). More importantly, a high X-ray imaging resolution of 16 lp/mm based on SC-Ag screen is demonstrated. Besides, rigid core skeleton reinforced by metallophilicity endows clusters M6 S6 L6 strong resistance to humidity and radiation. This work provides a new view for the design of efficient scintillators and opens the research door for silver clusters in scintillation application.

Copper(I) Halide Complex Featuring Blue Thermally Activated Delayed Fluorescence and Aggregate Induced Emission for Efficient X-ray Scintillation and Imaging

Developing solution-processable and stable scintillators with high light yields, low detection limits and high imaging resolutions holds great significance for flexible X-ray imaging. However, attaining an optimal equilibrium among X-ray absorption capacity, exciton utilization efficiency, and decay lifetime of scintillators remains a substantial challenge. Here, a new Cu(I) halide complex was synthesized in a mild condition. It exhibits intense blue thermally activated delayed fluorescence (TADF), remarkable aggregation-induced emission (AIE) characteristic, as well as good water-oxygen stability and photochemical stability. Notably, the complex shows excellent radiation resistance and efficient radioluminescence (RL) with an ultra-low detection limit of 42.5 nGyairs-1. This superior scintillation performance can be attributed to the synergistic effect of effective X-ray absorption by the heavy Cu2I2 core, the high radiation-induced exciton utilization rate in TADF process, and the remarkable suppression of non-radiative transitions by the restriction of intramolecular motions in solid state. Furthermore, the favourable solution processability of the complex facilitates the successful fabrication of a flexible film, achieving high-quality X-ray imaging with a resolution of 17.3 lp mm-1. This work highlights the potential of hybrid Cu(I) halides with AIE-TADF effects for high-energy radiation detection and imaging, opening up new avenues for the exploration of cost-effective and high-performance scintillators.