Lead‐free organic–inorganic hybrid scintillators for X‐ray detection

Abstract

Scintillators, which can convert high‐energy particles (X‐rays) into detectable low‐energy ultraviolet–visible–near‐infrared photons, are essential components of X‐ray detectors and show extensive practical applications in nondestructive detection and medical imaging. Traditionally, inorganic scintillators represented by CsI:Tl have achieved definite progress. However, the harsh preparation conditions, high production cost, and poor mechanical properties impede their potential development in the high‐end X‐ray imaging field. Organic–inorganic hybrid metal complexes could be excellent alternatives, by virtue of their structural and spectral tunability, good solution processability, and excellent photophysical properties. This review mainly focuses on eco‐friendly lead‐free metal (Mn2+, Cu+, Sb3+, Sn2+, Ge2+, Ln3+, etc.) complex scintillators. The luminescence mechanisms are introduced and the scintillation performance, such as light yield, limit of detection, imaging resolution, etc., is highlighted. Moreover, the current challenges and perspectives in this emerging field are described. It is hoped to provide some theoretical guidance for the continuous development of the new scintillator systems.

Mn(II)-Based Metal Halide with Near-Unity Quantum Yield for White LEDs and High-Resolution X-ray Imaging

“…Then, the trapped electrons and holes escape upon thermal fluctuation and diffuse to conduction and valence bands to form excitons, which are then transported to the Mn 2+ luminescent centers. Moreover, the optical transition of the excited Mn 2+ ions relaxes from 4 T 1 to 6 A 1 , resulting in fast and narrow band X-ray radioluminescence. ,, Different RL intensities through the scintillator flexible screen can be detected, and the final image is captured by an optical camera. As shown in Figure d, the first object selected for X-ray imaging is a ball-point pen with an internal metal spring.…”

“…For instance, using quaternary phosphonium ions as organic counterions, Ma’s group first reported that the photoluminescence quantum yield (PLQY) of green-emitting (C 38 H 34 P 2 )­MnBr 4 can reach up to 95%, with excellent X-ray scintillation properties such as a high light yield of ∼80 000 photon MeV –1 , a low detection limit of 72.8 nGy/s, and notorious intrinsic water stability . This study opens the door to low-dimensional Mn­(II)-based metal halide application in the X-ray imaging field, followed by many novel Mn­(II)-based metal halides reported based on the bulky organic units. , These bulky protonated ligands efficiently separate Mn centers and enhance the adjacent Mn–Mn distance, which can reduce electron interaction and prevent nonradiative energy transfer to quenching sites, leading to an enhanced PLQY. , Therefore, considering eco-friendly and plentiful on the earth, low toxicity, and excellent optical performance, the exceptional stability and absence of self-absorption in Mn­(II)-based metal halide emitters provide infinite exploring room for practical medical radiative imaging and display …”

Multiphase Transformation in Hybrid Copper(I)-Based Halides Enable Improved X-ray Scintillation and Real-Time Imaging

“…X-ray scintillators have the capability to transform high-energy X-rays into low-energy ultraviolet or visible light. − The ability of X-ray imaging that based on scintillator devices to detect the internal structure of opaque objects under X-rays has significantly contributed to medical or industrial inspection. − Among them, zero-dimensional (0D) metal halides have emerged as a novel scintillator material, because of their exceptional luminescence properties and ease of solution processing. − Given their excellent solution processability, 0D metal halides are used to prepare scintillation films suitable for imaging applications. − However, particle aggregation within the scintillation film ultimately reduces transparency, thereby causing luminescence bursts that limit the practical use of such films in X-ray scintillation imaging.…”

Zero-Dimensional Copper(I) Halide Microcrystals as Highly Efficient Scintillators for Flexible X-ray Imaging

“…X-ray scintillators, which can convert high-energy X-ray into visible light, have been widely applied in the fields of radiation exposure monitoring, safety inspection, nondestructive inspection, medical imaging, and so on. − Several key factors determine the practical application value of a scintillator, such as high light yield, low cost, high response rate, and high stability. − At present, a variety of inorganic crystal scintillators, such as LuAG:Ce, CsI:Tl, YAlO 3: Ce, Bi 4 Ge 3 O 12 crystals, have been widely developed and commercially utilized due to the advantages of high light yields and stabilities. − Nevertheless, these inorganic scintillators are synthesized through the harsh Czochralski method under extremely high temperatures and pressures, leading to high energy consumption and costs. , In addition, the large crystal size and grain boundaries prevent the fabrication of high-quality scintillation film in flexible X-ray imaging. , To address these issues, some organic scintillators have been developed but still suffer from the drawback of blocking X-rays due to their low absorption coefficients. , Considering the significance of dynamic X-ray flexible imaging for real-time monitoring of the internal curving structure of complex devices, it is still urgent and challenging to develop high-performance X-ray scintillators with high X-ray absorption coefficients, facile synthesis process, controllable crystal size, and excellent processability.…”