Scintillators, materials that produce light pulses upon interaction with ionizing radiation, are widely employed in radiation detectors. In advanced medical-imaging technologies, fast scintillators ...enabling a time resolution of tens of picoseconds are required to achieve high-resolution imaging at the millimetre length scale. Here we demonstrate that composite materials based on fluorescent metal–organic framework (MOF) nanocrystals can work as fast scintillators. We present a prototype scintillator fabricated by embedding MOF nanocrystals in a polymer. The MOF comprises zirconium oxo-hydroxy clusters, high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from 9,10-diphenylanthracene ligand emitters. Their incorporation in the framework enables fast sensitization of the ligand fluorescence, thus avoiding issues typically arising from the intimate mixing of complementary elements. This proof-of-concept prototype device shows an ultrafast scintillation rise time of ~50 ps, thus supporting the development of new scintillators based on engineered fluorescent MOF nanocrystals.Composites of fluorescent metal–organic framework nanocrystals in a polymer are exploited to create fast scintillators with a rise time of about 50 ps.
Abstract
Large Stokes shift fast emitters show a negligible reabsorption of their luminescence, a feature highly desirable for several applications such as fluorescence imaging, solar-light managing, ...and fabricating sensitive scintillating detectors for medical imaging and high-rate high-energy physics experiments. Here we obtain high efficiency luminescence with significant Stokes shift by exploiting fluorescent conjugated acene building blocks arranged in nanocrystals. Two ligands of equal molecular length and connectivity, yet complementary electronic properties, are co-assembled by zirconium oxy-hydroxy clusters, generating crystalline hetero-ligand metal-organic framework (MOF) nanocrystals. The diffusion of singlet excitons within the MOF and the matching of ligands absorption and emission properties enables an ultrafast activation of the low energy emission in the 100 ps time scale. The hybrid nanocrystals show a fluorescence quantum efficiency of ~60% and a Stokes shift as large as 750 meV (~6000 cm
−1
), which suppresses the emission reabsorption also in bulk devices. The fabricated prototypal nanocomposite fast scintillator shows benchmark performances which compete with those of some inorganic and organic commercial systems.
A Friedel–Crafts reaction was used to obtain covalent aromatic networks with high surface area and microporosity suited for CO2 and CH4 adsorption, even at low pressures. Starting from ...tetraphenylmethane and formaldehyde dimethyl acetal in different concentrations, the reaction yields porous polymers which were characterized with a wealth of experimental and computational methods. Thermogravimetry, infrared spectroscopy, and solid-state NMR were used to study the material structure. The pore distributions were measured by applying nonlocal density functional theory analysis to the adsorption isotherms of N2 at 77 K and Ar at 87 K (the latter being more suited for pore widths less than 10 Å). Carbon dioxide and methane were adsorbed at 273 and 298 K to evaluate the performance of these systems in gas capture, separation, and storage. A theoretical model of the porous network was defined to describe the ordered fraction of the material, with particular attention to ultramicropores. Ar, CO2, and CH4 adsorption in this model material was simulated by Monte Carlo techniques with a purposely optimized force field.
The COVID-19 pandemic is currently a severe challenge for healthcare workers, with a considerable impact on their mental health. In order to focus preventive and rehabilitation measures it's ...fundamental to identify risk factors of such psychological impairment. We designed an observational longitudinal study to systematically examine the psychological wellbeing of all employees in a large University Hospital in Italy, using validated psychometric scales in the context of the occupational physician's health surveillance, in collaboration with Psychiatric Unit.
The study started after ethical approval in August 2020. For each worker, the psychological wellbeing is screened in two steps. The first level questionnaire collects sociodemographic characteristics, personal and occupational COVID-19 exposure, worries and concerns about COVID-19, general psychological discomfort (GHQ-12), post-traumatic stress symptoms (IES-R) and anxiety (GAD-7). Workers who score above the cut-off in at least one scale are further investigated by the second level questionnaire composed by PHQ-9, DES-II and SCL-90. If second level shows psychological impairments, we offer individual specialist treatment (third level). We plan to follow-up all subjects to monitor symptoms and possible chronicization; we aim to investigate potential risk factors through univariate analysis and multivariate logistic regressions.
Preliminary results refer to a sample of 550 workers who completed the multi-step evaluation from August to December 2020, before vaccination campaign started. The participation rate was 90%. At first level screening, 39% of the subjects expressed general psychological discomfort (GHQ-12), 22% post-traumatic stress symptoms (IES-R), and 21% symptoms of anxiety (GAD-7). Women, nurses, younger workers, subjects with COVID-19 working exposure and with an infected family member showed significantly higher psychological impairment compared to colleagues. After the second level screening, 12% and 7% of all workers showed, respectively, depressive and dissociative symptoms; scorings were significantly associated with gender and occupational role. We are currently extending sample size and evaluating subjects over a period of further 12 months.
The possibility to perform a systematic follow-up of psychological wellbeing of all hospital workers, directly or indirectly exposed to pandemic consequences, constitutes a unique condition to detect individual, occupational, and non-occupational risk factors for psychological impairment in situations of prolonged stress, as well as variables associated with symptoms chronicization.
Molecular gas jars: Methane and carbon dioxide can be stored in open‐pore van der Waals crystals of tris‐o‐phenylenedioxycyclotriphosphazene at low partial pressure, whereas hydrogen, nitrogen, and ...oxygen are selectively excluded. Gas molecules participate in the supramolecular network of weak interactions and reside in the tight nanochannels in close contact with the surrounding aromatic rings (see picture).
Porous crystalline dipeptides absorb, reversibly from the gas phase, a series of volatile fluorinated ethers in use as anesthetics. Their vapor pressure was considerably reduced, with favorable guest ...capture and release. Variable channel sizes were customized for selective sorption and pressure thresholds were observed in the narrowest pores.
H,
C and
F MAS NMR coupled with ab initio conformational analysis and grand canonical Monte Carlo simulations highlight the guest loading and arrangement adopted in the congruent nanochannels, suggesting how the anesthetics can accommodate in biochemical receptors.
Modification of the optical and dielectric response upon nanocrystallization represents a tool for functionalizing glass-based materials and an alternative approach for data storage in optical media. ...Here we report results for Ga-containing alkali-germanosilicate glass undergoing thermally activated secondary phase separation and crystallization of native nanoheterogeneities with formation of dense dispersions (105μm−3) of γ-Ga2O3 nanocrystals in transparent glass ceramics. The shift of the Urbach tail in the UV absorption and the refractive index increase upon nanocrystallization are analyzed following Duffy’s approach and the Maxwell–Garnett description of refractive index in composite systems. The results clarify that native nanoheterogeneities consist of Ge-containing Ga-oxide and, consequently, composition changes occur between matrix and nanophase during nanocrystallization. Complex impedance data are analyzed to disentangle the electronic and ionic contributions to the dielectric response, pointing to a lowering of ionic polarizability parallel to the electronic polarizability increase. The analysis, aided by 71Ga NMR data, gives an insight into the relation between coordination changes and refractive and dielectric response, highlighting the role of non-bridging-oxygens and interphase.
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