2,659 research outputs found
Novel gamma-ray and thermal-neutron scintillators: Search for high-light-yield and fast-response materials
No full textIn this dissertation, we present bromide and iodide scintillators which have been investigated for the past four years. Three major groups of compounds were studied; lanthanide trihalides LnX3, (pseudo)-elpasolites M2ALnX6 and ternary halides AmLnnXo where M and A are alkali cations, Ln is a rare earth cation and X is a halide anion. Some materials show interesting gamma-ray-scintillation properties. LuI3: Ce3+, one of lanthanide trihalides, has a record high light output of 98,000 photons/MeV and a fast response of 35 ns. Other two groups, (pseudo)-elpasolites and ternary halides, show relatively low light yields. For thermal neutron scintillator, we focused with (pseudo)-elpasolites M2LiLnX6 and ternary halides LimLnnXo groups. Rb2LiYBr6: Ce3+ shows an excellent neutron peak resolution of 3.6%. This is the best neutron peak resolution ever reported. Together with the large Alpha/Beta ratio of 0.74, Rb2LiYBr6: Ce3+ offers the possibility of excellent neutron/gamma-ray discrimination. The highest thermal neutron scintillation light yield of 83,000 photons/neutron is also reported for Rb2LiYBr6: Ce3+.Applied Science
The incorporation of CsCu2I3 nanocrystals into polydimethylsiloxane matrix for X- and γ-ray scintillators
No full textRaw data was presented in the following manuscript: T. Haposan, M. Makowski, D. Kowal, L.J. Diguna, M.E. Witkowski, S. Mahato, W. Drozdowski, A. Arramel, M.D. Birowosuto, The Incorporation of CsCu2I3 Nanocrystals into Polydimethylsiloxane Matrix for X- and γ-Ray Scintillators, Phys. Status Solidi RRL 19, (2025) 24010298. https://doi.org/10.1002/pssr.202400298.The attached ZIP contains data of radioluminescence (RL) as a function of temperature, pulse height spectra (PHS) and scintillation time profile (STP) of CsCu2I3 nanocrystals embedded in polydimethylsiloxane matrix.</p
Control of perovskite luminescence with metamaterials
No full textWe show that luminescence spectra of solution-processable metal-halide perovskite films can be controlled by nanopatterning, leading to up to five-fold increase of luminescence yield. We engineered the optical response of the perovskite films using metamaterial design concepts and, as proof of principle, we fabricated all-perovskite dielectric metasurfaces and hybrid metal-perovskite metamaterials which show significantly enhanced luminescence emission and controlled spectral response throughout the visible region. The all-dielectric metamaterials were engraved by direct focused ion beam milling (FIB) onto thin films of methylammonium lead iodide perovskite (CH3NH3PbI3) spin-coated on quartz substrate. The perovskite metasurfaces show vivid structural color tuning and strong field enhancement, dependent on the geometrical parameters of the nanometer sized metamolecules. We observed up to a five-fold Purcell enhancement of both photo- and cathodo-luminescence emission compared to the unstructured films. We also discuss hybridization of perovskite films with plasmonic metamaterials and metal-semiconductor-metal slab waveguide geometries to provide higher control on the light extraction properties. Our results prove that nanostructuring and hybridization of perovskites with metamaterials are viable routes to engineer tunable structural colour and radiative emission properties on-demand, thus defining a new paradigm to increase the efficiency, control the luminescence spectrum, and improve light extraction and directivity of light-emitting devices
Luminescence of all-dielectric solution-processed perovskite metamaterial
No full textWe demonstrate that periodic subwavelength nanostructuring of solution-processed organolead halide perovskite films creates optical resonances, position of which can be controlled by design. Such metamaterial nanostructuring strongly enhances photo- and cathodo-luminescence of the films
X-ray scintillation in lead halide perovskite crystals
No full textCurrent technologies for X-ray detection rely on scintillation from expensive inorganic crystals grown at high-temperature, which so far has hindered the development of large-area scintillator arrays. Thanks to the presence of heavy atoms, solution-grown hybrid lead halide perovskite single crystals exhibit short X-ray absorption length and excellent detection efficiency. Here we compare X-ray scintillator characteristics of three-dimensional (3D) MAPbI 3 and MAPbBr 3 and two-dimensional (2D) (EDBE)PbCl 4 hybrid perovskite crystals. X-ray excited thermoluminescence measurements indicate the absence of deep traps and a very small density of shallow trap states, which lessens after-glow effects. All perovskite single crystals exhibit high X-ray excited luminescence yields of >120,000 photons/MeV at low temperature. Although thermal quenching is significant at room temperature, the large exciton binding energy of 2D (EDBE)PbCl 4 significantly reduces thermal effects compared to 3D perovskites, and moderate light yield of 9,000 photons/MeV can be achieved even at room temperature. This highlights the potential of 2D metal halide perovskites for large-area and low-cost scintillator devices for medical, security and scientific applications
Organometallic Perovskite Metasurfaces
No full textResearchers show that solution-processed organometallic halide perovskites provide a high index, low-loss platform for realizing metasurfaces with high Q-factor resonances at visible frequencies in the search for alternative dielectric photonic materials. Organolead halide perovskites are emerging solution-processable materials with outstanding optoelectronic properties. Among them, methylammonium lead iodide perovskite, CH3NH3PbI3, has proven to be an exceptional light harvester for hybrid organic–inorganic solar cells, which has achieved an impressive NREL certified power conversion efficiency over 20%, and remarkable performance in a variety of device architectures
Effect of dual-organic cations on the structure and properties of 2D hybrid perovskites as scintillators
No full textRaw data presented in the following manuscript: M.A. K. Sheikh, F. Maddalena, D. Kowal, M. Makowski, S. Mahato, R. Jedrzejewski, R. Bhattarai, M.E. Witkowski, K.J. Drozdowski, W. Drozdowski, C. Dang, T.D. Rhone, M.D. Birowosuto, Effect of Dual-Organic Cations on the Structure and Properties of 2D Hybrid Perovskites as Scintillators, ACS Applied Materials Interfaces 16, (2024) 25529-25539. https://doi.org/10.1021/acsami.4c01741Attached files consist of absorption spectra, photoluminescence (PL), time-resolved PL (TRPL), X-ray luminescence (RL) as a function of temeprature, low temperature thermoluminescence (ltTL) measurement data.</p
George McClellan [1849-1913]: A Memoir read before the College of Physicians of Philadelphia, by J. Chalmers Da Costa, M.D., LL.D., Samuel D. Gross Professor of Surgery in Jefferson Medical College
No full textA memoir of Dr. George McClellan (1849-1913). Dr. McClellan was the author of the book Regional Anatomy, and grandson of George McClellan, M.D.; the founder of Jefferson Medical College
Nanopatterning-enhanced perovskite luminophores
No full textWe demonstrate that nanopatterning of solution-processable metal-halide perovskite films can be used to control their luminescence spectra and lead to up to five-fold increase of luminescence yield
2000 Commencement Address: G. Timothy Johnson, M.D.
No full textTimothy Johnson, M.D., medical editor for ABC News will deliver the principal address and receive an honorary degree at the 154th commencement exercises at the College of the Holy Cross on Friday, May 26, beginning at 10:30 a.m. at Fitton Field.
Johnson, one of the nation’s leading medical communicators of health care information, has provided commentary on medical problems and answers for viewers since 1975. In addition to commentary on Good Morning America, Johnson provides on-air analysis of medical news for World News Tonight, Nightline and 20/20. He consults with ABC News regardingcoverage of medical news. He is also medical editor for WCVB-TV, Channel 5 in Boston.
Johnson holds joint positions in medicine at Harvard University and Massachusetts General Hospital in Boston. He is the founding editor of the Harvard Medical School Health Letter and co-editor of the Harvard Medical School Health Letter Book. He is also coeditor of the book, “Your Good Health,” published by Harvard Press, as well as co-author with former US Surgeon General Dr. C. Everett Koop of the book, “Let’s Talk,” published by Zondervan in 1992.
He originally intended to join the ministry and graduated from the North Park Seminary in 1963. Two years later he decided to enter medicine. Johnson, who is a Phi Beta Kappa graduate of Augustana College, graduated summa cum laude from Albany Medical College and holds a master’s degree in public health from Harvard University. Johnson served as an assisting minister at the Community Covenant Church in West Peabody, Mass.https://crossworks.holycross.edu/commence_address/1012/thumbnail.jp
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