Lithium-Doped Two-Dimensional Perovskite Scintillator for Wide-Range Radiation Detection

Two-dimensional lead halide perovskites have demonstrated their potential as high-performance scintillators for X- and gamma-ray detection, while also being low-cost. Here we adopt lithium chemical doping in two-dimensional phenethylammonium lead bromide (PEA)2PbBr4 perovskite crystals to improve the properties and add functionalities with other radiation detections. Li doping is confirmed by X-ray photoemission spectroscopy and the scintillation mechanisms are explored via temperature dependent X-ray and thermoluminescence measurements. Our 1:1 Li-doped (PEA)2PbBr4 demonstrates a fast decay time of 11 ns (80%), a clear photopeak with an energy resolution of 12.4%, and a scintillation yield of 11,000 photons per MeV under 662 keV gamma-ray radiation. Additionally, our Li-doped crystal shows a clear alpha particle/gamma-ray discrimination and promising thermal neutron detection through 6Li enrichment. X-ray imaging pictures with (PEA)2PbBr4 are also presented. All results demonstrate the potential of Li-doped (PEA)2PbBr4 as a versatile scintillator covering a wide radiation energy range for various applications

Dataset for Organometallic Perovskite Metasurfaces

Dataset supporting: Behrad Gholipour et al. Organometallic Perovskite Metasurfaces. Advanced Materials.</span

Organometallic perovskite metasurfaces

Dielectric metamaterials are widely explored as low-loss alternative to their plasmonic counterparts, which suffer from substantial Ohmic losses at optical frequencies. Here we demonstrate that organometallic perovskites, emerging solution-processable materials with outstanding optoelectronic properties and high index of refraction, provide a platform for all-dielectric metamaterials operating at visible frequencies. We show organolead halide perovskite metasurfaces with structural colouring tunable across the visible spectrum through sub-wavelength structuring. Moreover, we demonstrate that nanostructured perovskite films exhibit enhanced photoluminescence. We observed a three-fold increase of the luminescence yield and comparable reduction of luminescence decay time in comparison with unstructured perovskites films. We argue that nanostructured, solution processable organometallic perovskites metamaterials prepared by nanoimprint could be a low cost solution for photovoltaic energy conversion, large-area light-emitting devices, and artificial colouring for display applications

Spectral control in metal halide perovskites metasurfaces

We demonstrate that nanostructuring and hybridization of perovskites with metasurfaces allow to engineer structural colour and radiative emission properties, providing new opportunities to control emissivity and directivity of light-emitting devices

Disordered polymer antireflective coating for improved perovskite photovoltaics

Light management through low index medium, such as antireflective coating (ARC) provides practical solution to improve the efficiency of photovoltaics. However, a brute-force development of photonic structure on ARC is not necessarily useful, because of random scattering associated with impediment of light transmission. Here, we leverage the concept of disorder, rather than random, structured on ARC for improving efficiency without modifying original architecture of thin-film photovoltaics. We demonstrate a disordered polymer that leads to a total reflectance of 5% while demonstrating a high transmission of 94% across 300 to 820 nm wavelength. Next, we find that the arrangement of disordered points and line arrays constructing the polymer seems to be the key to control bandwidth performance of the ARC. Finally, we apply this into Cs0.05(MA0.17FA0.83)0.95Pb(I0.83Br0.17)3 perovskite, and through experiments with wave-optics and full-device simulation, show a 1.6-fold absorption gain leading to 19.59% power-conversion-efficiency by the disordered ARC.Ministry of Education (MOE)National Research Foundation (NRF)Accepted versionThis work is supported by the National Research Foundation, Prime Minister’s Office, Singapore under Energy Research Innovation Program (Grant number, NRF2015EWT-EIRP003-004 and NRF-CRP14-2014-03 and Solar CRP:S18-1176-SCRP), and Ministry of Education (MOE2016‐T2‐1‐052)

Direct imaging of weak-to-strong-coupling dynamics in biological plasmon–exciton systems

Optical coupling plays a pivotal role in nanophotonic systems, which can be divided into weak, intermediate, and strong-coupling regimes. Monitoring optical coupling strength is, therefore, the key to understanding light–matter interactions. State-of-the-art approaches based on spectral measurements offer the power to quantify and characterize optical coupling strength at a single cavity level. However, it remains challenging to dynamically characterize coupling strength during the transition from strong- to weak-coupling regimes for many systems simultaneously. Here, a far-field imaging technique is reported that can directly monitor optical coupling dynamics in plasmon–exciton systems, allowing multiple nanocavity emissions to be characterized from weak- to strong-coupling regimes. Light-harvesting biomolecules—chlorophyll-a—is employed to study dynamic light–matter interactions in strongly coupled plasmonic nanocavities. Identification of coupling strength is achieved by extracting red, green, and blue (RGB) values from dark-field images and an enhancement factor from fluorescence images. Lastly, the ability to monitor subtle changes of coupling dynamics in bioplasmonic nanocavity is demonstrated. These findings may deepen the understanding in light–matter interactions, paving new avenues toward applications in quantum-based biosensing and imaging.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Y.-C.C. would especially like to thank the financial support from A*STAR-Singapore under its AME IRG-Grant (Grant No. A20E5c0085). P.C.W. acknowledges the support from Ministry of Science and Technology (MOST), Taiwan (Grant Nos. 108-2112-M-006-021-MY3 and 110-2124-M-006-004), and in part from the Higher Education Sprout Project of Ministry of Education (MOE) to the Headquarters of University Advancement at National Cheng Kung University (NCKU). P.C.W. also acknowledges the support from Ministry of Education (Yushan Young Scholar Program), Taiwan. C.D. thanks the financial support from the Ministry of Education, Singapore, under its AcRF Tier 2 grant: MOE-T2EP50121-0012. M.K. thanks the financial support from the Ministry of Education under grant MOE-T2EP50120-0001

(BZA)₂PbBr₄: A potential scintillator for photon-counting computed tomography detectors

Due to recent development in detector technology, photon-counting computed tomography (PCCT) has become a rapidly emerging medical imaging technology. Current PCCT systems rely on the direct conversion of X-ray photons into charge pulses, using CdTe, CZT, or Si semiconductor detectors. Indirect detection using ultrafast scintillators coupled to silicon photomultipliers (SiPM) offers a potentially more straightforward and cost-effective alternative. In this work a new 2D perovskite scintillator, benzylamonium lead bromide (BZA)2PbBr4, is experimentally characterised as function of temperature. The material exhibits a 4.2 ns decay time under X-ray excitation at room temperature and a light yield of 3700 photons/MeV. The simulation tool developed by Van der Sar et al. was used to model the pulse trains produced by a SiPM-based (BZA)2PbBr4 detector. The fast decay time of (BZA)2PbBr4 results in outstanding count-rate performance as well as very low statistical fluctuations in the simulated pulses. These features of (BZA)2PbBr4, combined with its cost-effective synthesis make (BZA)2PbBr4 very promising for PCCT.RST/Luminescence MaterialsRST/Medical Physics & Technolog

Surface molecular doping of all-inorganic perovskite using zethrenes molecules

We present an optical and photoelectron spectroscopic study to elucidate the interfacial electronic properties of organic-inorganic semiconductor heterojunctions formed in a kinetically blocked heptazethrene triisopropylsilyl ethynylene (HZ-TIPS) and its homologue, octazethrene (OZ-TIPS) on an all-inorganic perovskite cesium lead bromide (CsPbBr3) surface. The photoluminescence behavior of the underlying perovskites upon differing molecular doping conditions was examined. It turns out that the charge transfer dynamics of thermally-evaporated OZ-TIPS molecule exhibited a faster average lifetime than that of the HZ-TIPS case suggesting the importance of the biradical state in the former molecule. An interfacial dipole was formed at the interface due to the competing interaction between the dispersion force of the bulky TIPS-substituent group and the attractive van der Waals interaction at the first few layers. Photoemission spectroscopy of the physisorbed HZ-TIPS shows chemical shifts, which indicates electron transfer from HZ-TIPS molecules to the CsPbBr3 perovskite single crystal. In contrast, the adsorbed OZ-TIPS molecular layer on CsPbBr3 demonstrates the opposite trend indicating a hole transfer process. The average molecular orientation as determined by near edge X-ray absorption fine structure (NEXAFS) suggests that the HZ-TIPS molecular plane is generally lifted with respect to the perovskite surface. We suggest that the nature of the closed-shell electronic ground state of HZ-TIPS could contribute to the formation of interfacial dipole at the molecule/perovskite interface.NRF (Natl Research Foundation, S’pore)MOE (Min. of Education, S’pore)Accepted versio