Large scale light source facilities such as synchrotrons and X-ray free electron lasers (XFELs) are used across the breadth of scientific applications from helping to develop new energy storage materials to understanding viruses and aiding the development of vaccines. The demands of making faster measurements with high fluxes of X-rays has driven the development of new readout electronics and supported the adoption of direct detection materials. Driven by the upgrade to “3rd generation” synchrotrons, Si based photon counting detectors have been used on synchrotrons since the mid-2000s [1] with high-Z semiconductor options, such as CdTe, following over the next decade. In parallel, similar technologies were in development for medical-CT, but the certification requirements and barriers to entry in the medial field meant it was not until the 2020s that the first photon-counting detector CT systems reached the clinic [2].

Whereas the requirement of medical CT detectors to measure hard X-rays up to a flux of 109 photon/mm2/s at a resolution of 0.3-0.5mm is unlike to change, the synchrotron detector technology is being pushed further. Spatial resolutions less than 0.1mm are already commonplace and the advent of 4th generation synchrotrons is pushing the flux requirements up to 1012 photons/mm2/s. In parallel, XFELs which deliver very intense femto-second X-ray pulse are moving to continuous repetition rates in the MHz range which will require X-ray detectors to operate at similarly high fluxes and small pixel sizes.

Currently, the best candidate detector material for these applications is CdZnTe. It has the benefit of high X-ray stopping power, low leakage current, good electron charge transport properties, is available with fine pixelation and is compatible with some standard interconnection techniques [3]. However, CdZnTe is melt grown in 3-inch boules that limit the single die size and has limited hole transport properties that may ultimately limit the operating flux. The rapid development of Perovskite and similar detector materials have demonstrated the potential of these materials as hard X-ray detectors [4]. The challenges and opportunities that these new materials may bring to the scientific X-ray detector community will be discussed.

Whilst the ~70 light source facilities around the world may not represent the largest volume detector market, they have the benefit of being research facilities that can support the development and advancement of new detectors materials and readout technology to push the boundaries of X-ray detection.

Currently, there is a significant need to increase the spatial resolution of medical X-ray imaging while maintaining high detection efficiency to provide high-quality images at low radiation doses [1]. This pushes research for the development of novel detector materials and architectures. Besides diverse state-of-the-art detector materials such as Si a-Se, and CdTe, recently, a novel class of semiconductors - metal halide perovskites - emerged as promising materials for radiography and computed tomography applications. However, existing studies lack persuasive examples of fully integrated perovskite detectors that would combine a high spatial resolution of multi-pixel detectors together with high detection efficiency (DE) [2], for which direct integration of single crystals on the readout substrates would be required. Here we show a method of fabricating high-quality, thick large-grain polycrystalline CsPbBr₃ films by melt growth directly on pixelated glass interposers. The obtained detector arrays show a remarkable 20 lp mm^-1 spatial resolution with a DE of 75.4% and low noise equivalent dose (NED) of ca. 46 photons for 22 keV X-rays under a low reverse bias voltage. The combination of these characteristics results in unprecedently, for charge-integrating mode, high values of 20% for detective quantum efficiency (DQE) at the Nyquist frequency. Single-pixel devices demonstrate single-photon counting performance for γ-radiation with an energy-resolved peak of ²⁴¹Am. Melt-grown CsPbBr₃ films, featuring a unique combination of detection efficiency, scalable fabrication, and cost-effectiveness, are promising for the development of high spatial resolution, low-dose X-ray imaging systems.

Hybrid metal halide perovskites have emerged as promising materials for X-ray detection due to their scalable, cost-effective, and robust solution growth, combined with their ability to detect single gamma-photons under high applied bias voltages. Despite these advantages, their rapid degradation under high electric fields, a result of mixed electronic-ionic conduction, has hindered the development of stable and efficient perovskite-based X-ray detectors.

To address this limitation, we previously demonstrated a photovoltaic mode of operation at zero-voltage bias, using thick methylammonium lead iodide (MAPbI₃) single-crystal films (up to 300 µm) grown directly on hole-transporting electrodes via the space-confined inverse temperature crystallization (ITC) method [1].  These devices exhibited near-to-ideal performance, long-term stability, 88% detection efficiency, and a noise equivalent dose of 90 pGyair with 18 keV X-rays. However, we observed experimentally that the performance of MAPbI₃ devices degrades significantly beyond thicknesses of 200 µm, presenting a challenge for their application in scenarios requiring thicker crystals for higher sensitivity.

Building upon this foundation, we now present [2] advances in compositional engineering that enable up to 100% charge extraction in perovskite single crystals with thicknesses reaching 900 µm. These high-quality crystals exhibit extended charge carrier lifetimes, enabling efficient absorption of X-rays at energies of both 18 keV and 45 keV and complete charge collection. This marks a significant step forward in perovskite detector technology, as the thicker crystals allow for higher detection sensitivity while maintaining excellent material stability. Uniquely, these devices operate with no external bias, a breakthrough in X-ray detection technology. Unlike other semiconductor direct X-ray detectors, which require extremely high electric fields generated by hundreds of volts to achieve efficient charge collection, our perovskite detectors achieve 100% charge extraction under zero-voltage bias. This sets a new standard for X-ray detectors, combining superior performance with simplicity in operation.

In conclusion, this study introduces a novel approach to perovskite X-ray detectors by combining compositional engineering with advanced solution growth techniques. This results in devices with enhanced charge extraction efficiency, superior carrier lifetimes, and robust long-term stability, paving the way for cost-effective, high-performance X-ray imaging technologies.

[1] Sakhatskyi, K.† Turedi, B.†, Bakr, O. M, Kovalenko, M. V. et al. Nature Photonics 2023, 17(6), 510-517.

†equal first-authors

[2] unpublished

Fast and highly emissive plastic scintillators, usually made of a polymeric scintillating matrix that host a fluorescent dye, are requested for many advanced applications where high signal-to-noise ratio is required in a short time window. For example, to detect high rate events avoiding pile up in high energy physics experiments at the energy and intensity frontiers to face the challenges of unprecedented event rate and severe radiation environment, or to quickly acquire high quality image at low dose in medical applications as in the time-of-flight positron emission tomography (TOF-PET) imaging technique, where coincidence time resolution (CTR) of tents of picoseconds time is desired. Unfortunately, their low density results into a low stopping power of the high energy radiation and their scintillation light yield 𝜙𝐿𝑌, defined as the ratio between the number of emitted photons and the energy deposited in the system, is lower than the one of best inorganic scintillators. This detrimentally reduces the emitted light output and consequently the detector sensitivity.
A common strategy to improve the 𝜙𝐿𝑌 is the loading of polymeric scintillators with high Z elements or dense nanoparticles (NPs) to enhance the stopping power of liquid and polymeric conjugated scintillators [1-3]. Otherwise, to still keep the good emissive properties of conjugated systems, a possible solution is to use scintillating metal-Organic Framework (MOF) crystalline s hybrid system composed of conjugated ligands connected by heavy-element containing linking nodes [4-7].
I will present the most recent results on the development of these system highlighting the main peculiar photophysical of the scintillation process in these materials and the perspectives for their future uses.

Proton therapy is a cutting-edge cancer treatment that uses high-energy proton beams to target tumors with remarkable precision. Unlike conventional radiation therapy based on high energy photons, proton therapy allows for a more localized deposition of energy, delivering a high dose to the tumor while minimizing damage to surrounding healthy tissues. This precision is especially crucial in treating cancers located near critical organs or in pediatric patients, where sparing healthy tissue is essential to reducing long-term side effects.

The success of proton therapy relies heavily on accurate dose delivery. Even small deviations in the proton beam’s range or energy due to misalignment issues can lead to under-dosing the tumor or over-dosing healthy tissues. Therefore, during proton therapy is even more important the monitoring in real-time of the dose delivered to the patients to ensure treatment safety and effectiveness. In fact, real-time and in-situ dose monitoring systems can detect discrepancies during treatment, enabling immediate corrections and improving patient outcomes.

Organic semiconductors and lead halide perovskites recently demonstrated their potentiality for the detection and spatial mapping of MeV protons^1–4. These two classes of materials in the form of thin films fully benefit from solution-based fabrication processes that allow fast and easy large-area coverage over flexible thin plastic substrates with low-cost procedures.

Here, we report about the employment of organic and perovskite thin films as the active layer of proton direct and indirect detectors for the real-time and in-situ monitoring of the dose delivered to the patients during proton therapy treatments.

1.         Fratelli, I. et al. Real-Time Radiation Beam Monitoring by Flexible Perovskite Thin Film Arrays. Advanced Science (2024).

2.         Fratelli, I. et al. Direct detection of 5-MeV protons by flexible organic thin-film devices. Sci Adv 7, eabf4462 (2021).

3.         Basiricò, L. et al. Mixed 3D – 2D Perovskite Flexible Films for the Direct Detection of 5 MeV Protons. Advanced Science 2204815, 1–8 (2022).

4.         Calvi, S. et al. Flexible fully organic indirect detector for megaelectronvolts proton beams. npj Flexible Electronics 1–11 (2023).

Recently, near-infrared (NIR) photodetectors are gaining increasing attention due to the significant development of automotive vehicles, smart phones, machine vision, augmented reality, and so on. Particularly, some high-throughput applications such as optical communication and computed axial tomography also require NIR photodetectors to response fast. In the wavelength region between 850 and 1100 nm, where LiDAR (light detection and ranging) technology is operated, silicon photodetectors dominate the current market owing to their low cost and easy integration with fabrication procedures in industry. However, silicon photodetectors are usually bulky and require high-temperature purification processes, making them less attractive for wearable devices. In this respect, emerging absorbers including organic materials, lead-halide perovskites, and chalcogenide quantum dots are perfect alternatives to silicon because they can be synthesized using low-temperature solution-processing methods. Nevertheless, these emerging absorbers are also facing different challenges. For instance, organic materials have poor carrier transport, and lead-halide perovskites are not stable in air. Moreover, almost all the efficient NIR photodetectors based on lead-halide perovskites and chalcogenide quantum dots contain Pb or Cd, which raises great concerns on toxicity as well as environmental pollutions. It is also worth noting that only a handful of NIR photodetectors based on organic materials or PbS have reported a cut-off frequency exceeding 300 kHz, indicating that a fast photo-response is still challenging to achieve in these solution-processed photodetectors, especially in the NIR region.

In this work, we aim to develop fast NIR photodetector using a perovskite-inspired material – AgBiS₂, which has an ideal bandgap (~1.2 eV) along with strong absorption coefficients (> 10⁵ cm^-1 in the visible and UV region), and is only composed of RoHS-compliant (low toxicity) elements. We found that AgBiS₂ photodetectors could exhibit high cut-off frequencies either under white light (> 1 MHz) and NIR light (approaching 500 kHz) illumination, which correspond to rise/fall times of only a few microseconds. Such fast photo-response is attributed to the short transit distances of photo-excited charge-carriers in the ultrathin AgBiS₂ layer, where drift transport could dominate. Temperature-dependent transient current measurements also revealed ion migration to play a crucial role in limiting the photo-response speed and increasing the dark currents of AgBiS₂ photodetectors, while its detrimental impacts can be effectively suppressed by carefully tuning the thickness of the AgBiS₂ layer. These outstanding characteristics enable an air-stable, real-time, and solution-processable heartbeat sensor to be realized based on our AgBiS₂ NIR photodetector, demonstrating the great potential of AgBiS₂ devices in high-throughput systems.

Title: Project MULANS: Multi-layered Nano Scintillators

Author(s), Abigail Seddon, Guillaume Bertrand, Ludovic Tortech

Affiliation, Commissariat à l’énergie atomique et aux énergies alternatives, Saclay, France

E-mail: abigail.seddon@cea.fr

Scintillators are materials that emit light when bombarded with high-energy particles (β, γ) or X-rays; they convert incoming X-ray radiation into visible light that can then be captured using film or photosensors. For each application wihtin radiodetection, there is an appropriate organic or inorganic scintillator exhibiting the requirements of the desired measurements. However, for all scintillators two phenomena are an ongoing challenge to master. (1) The scintillation light emission is isotropic, hindering efficient light collection. (2) Ultra-fast decay cannot be achieved without a drastic loss of light production. Herein, a multi-layered scintillation device is reported, exhibiting high light collection and ultra-fast decay (low afterglow) achievable via the Purcell effect. The Purcell effect is the enhancement of a quantum system's spontaneous emission rate by its environment.² By using a substrate of either a layer of metal or alternating layers of metal and dielectric material, it was found that the light conversion efficiency can be increased by 250 percent for a scintillation device (Figure 1) compared to a conventional homogeneous scintillator.¹

A proof-of-concept of a novel bilayer Purcell device is reported, consisting of an organic scintillation molecule, such as POPOP or 1,9-diphenylanthracene, with an inorganic dielectric such as CuBr. The devices are fully characterised strcuturally, including by SEM-EDX, XPS, and AFM. The difference in optical properties between each layer enables the angular enhancement observed by photophysics and radiphysics. Moving forwards, devices may provide better light yield and reduced decay times, inhibiting afterglow with adequate spectral shaping via the Purcell effect. Real-world results include enabling faster and better resolution scans. This is the first report of a device of this kind.

A multilayer luminescent design concept is presented to develop energy sensitive radiation-beam monitors on the basis of colorimetric analysis. Each luminescent layer within the stack consists of rare-earth-doped transparent oxide of optical quality and a characteristic luminescent emission under excitation with electron or ion radiation. For a given type of particle beam (electron, protons, α particles, etc.), the penetration depth and the energy loss at a particular buried layer within the multilayer stack vary with the initial energy of the beam. The intensity of the luminescent response of each layer depends on the energy deposited by the radiation beam within the layer, so characteristic colour emission will be achieved if different phosphors are included in the layers of the luminescent stack. Phosphor doping, emission efficiency, layer thickness, and multilayer design are key parameters relevant to achieving a broad colorimetric response. Case examples are designed and fabricated to illustrate the capabilities of these new type of detector to evaluate the kinetic energy of either e- beams of a few keV or α particles of a few MeVs.

Chemically synthesised semiconductor nanocrystals are gaining momentum as ultrafast nanoscintillators for radiation detection. In particular, quantum-confined lead halide perovsite (LHP) nanocrystals in polymeric matrices combine the high density of Pb-based scintillators with high production scalability, extreme radiation hardness, and unique scintillation properties governed by a multiexciton generation and decay process. This results in competitive efficiencies with Pb-enriched commercial plastic scintillators, improved stability to radiation damage and ultrafast emission lifetimes, largely below 0.5 ns, which promise important advances in fast timing applications from medical tomography to high energy physics. In this talk, I will review the fundamental mechanisms of nanoscale scintillators, highlighting the impact of multi-exciton generation processes and showing how carrier dynamics optical experiments can effectively anticipate particle size effects on both scintillation timing and efficiency. The potential of single nanocrystals is further extended by demonstrating collective scintillation processes made possible by the unique electronic structure of LHP nanocrystals. In addition to isolated nanocrystals, innovative ways to improve performance in high-density plastic matrices and supermolecular nanocrystal architectures will be presented and discussed.  

Lead-Halide hybrid Perovskites are recently emerging as promising materials for high energy radiation detection thanks to the combination of high absorption coefficient, excellent transport properties, even in polycrystalline films, and their solution processability. Here we present Perovskite based X-ray detectors employing a perovskite-polymer composite thin film as active layer. The use of polymeric template for the perovskite growth allows a precise control of the active layer thickness and compactness, and confers to the device unconventional resistance to moisture and performances.[1] The performances of the active perovskite layer, inserted in a photodiode architecture, were studied under 40kV X-ray radiation. Remarkably, a top sensitivity of 5.5±0.2 μC Gy-1 cm-2 was measured for the device operating in passive mode (0V), coupled with exceptional stability. The samples were stored in air for 629 days tracking the performance degradation retaining 97% of the initial sensitivity. [2] A general overview of the potential of polymeric perovskite-based composites for x-ray detection in given.[3,4] 

References
[1] A Giuri, S Masi, A Listorti, G Gigli, S Colella, CE Corcione, A Rizzo, 'Polymeric rheology modifier allows single-step coating of perovskite ink for highly efficient and stable solar cells', 2018, Nano Energy 54, 400-408
[2] M. Verdi, A. Giuri, A. Ciavatti, A. Rizzo, L. Basiricò, S. Colella, B. Fraboni, 'Record stability for perovskite-based X-ray detectors through the use of polymeric template', under submission, 2023, Advanced Materials Interfaces 10 (18), 2300044.

[3] Incorporation of Functional Polymers into Metal Halide Perovskites thin-films: from interactions in solution to crystallization, 2023 Materials Advances.

[4] Implication of polymeric template agent on the formation process of hybrid halide perovskite films, Antonella Giuri, Rahim Munir, Andrea Listorti, Carola Esposito Corcione, Giuseppe Gigli, Aurora Rizzo, Aram Amassian, Silvia Colella, 2021, Nanotechnology.

Metal halide perovskites (MHPs) are emerging as promising materials for next-generation radiation detectors due to their high atomic number, efficient X-ray absorption, low exciton binding energy, and unique electronic structure, which enhances charge carrier mobility and collection efficiency [1-3]. Furthermore, their solution processability and mechanical flexibility make them ideal for integration into lightweight, flexible X-ray detector designs. In this work, we report the fabrication and characterization of lightweight perovskite-embedded membranes (PEMs) by spin-coating triple-cation perovskite onto hydrophilic membranes. The detectors were tested under continuous X-ray irradiation using a laboratory X-ray source and pulsed X-ray conditions at the KMC-3 XPP beamline of BESSY II, enabling comprehensive performance evaluation in diverse radiation environments. Pulsed X-ray testing was conducted with energies ranging from 7 keV to 16 keV and at different voltages.

With this approach, a sensitivity of 0.97 × 10⁵ μC/Gy_air.cm² under continuous 8 keV irradiation at a dose rate of 0.094 µGy_air/s at 100 V was achieved. Additionally, we investigated the impact of polymer treatment on the X-ray detection performance. By adding polymers, we further increased the sensitivity to 2.38 × 10⁵ μC/Gy_air.cm² for the polymer-treated devices under the same conditions.

Our results show that polymer treatment improves the photoluminescence quantum yield (PLQY) and increases the crystallinity of the perovskite at the 100 planes, indicating enhanced material quality. These improvements correlate with a notable increase in X-ray sensitivity in the polymer-treated devices.

Notably, the detectors demonstrated X-ray response even at 0 V, with polymer-treated device showing a sensitivity of 0.93 × 10² μC/Gy_air.cm², while the control devices showed a sensitivity of 0.42 × 10² μC/Gy_air.cm² under continuous 8 keV irradiation at a dose rate of 184.7 µGy_air/s. Under both continuous and pulsed X-ray conditions, polymer-treated devices consistently outperformed untreated controls, underscoring their superior performance and robustness.

The polymer additives act as passivation agents, reducing defect states and improving charge transport properties, which contribute to the enhanced X-ray detection performance. These findings position polymer treatment as a key strategy for optimizing the performance of flexible perovskite X-ray detectors.

In conclusion, this study demonstrates the feasibility of developing high-performance, flexible perovskite X-ray detectors with enhanced sensitivity. These advancements open the path towards lightweight, portable, and wearable radiation monitoring systems, creating new opportunities for advanced radiation detection.