arXiv subjects

Angelo Monguzzi

Publications and source records attributed to Angelo Monguzzi.

7 recordsLinked to original sources

arXiv2026

Excited states engineering maximizes singlet generation by triplet fusion in conjugated systems

Photon upconverters are anti Stokes emitters capable of generating photons with higher energy than those absorbed. This behavior can be achieved through different mechanisms, which are extensively studied for applications in imaging, anticounterfeiting, information encryption and most importantly, solar energy technologies. Among these mechanisms, photon upconversion based on sensitized triplet-triplet annihilation (sTTA-UC) is particularly attractive because it operates under low intensity, incoherent light. In sTTA UC, two optically dark triplet states of a conjugated annihilator fuse upon collision to populate a higher energy fluorescent singlet, with the triplets initially generated via energy transfer from a lower energy sensitizer. Here we introduce a general molecular design strategy to maximize singlet generation through TTA. By selective substitution, we engineered a naphthalene derived annihilator with an excited state energy landscape that strongly favors singlet formation, achieving yields up to 0.83. When combined with an appropriate triplet sensitizer, the system delivers stable UV/visible upconversion peaking at 390 nm, with an absolute upconversion yield about 0.19 and an activation excitation intensity threshold lower than 0.1 suns under non-coherent broadband excitation fully compatible with the requirements of solar powered technologies.

physics.optics↗

arXiv2025

Ultrafast scintillating metal-organic frameworks films

Compositionally engineered metal-organic frameworks (MOFs) have been designed and used to fabricate ultrafast scintillating films with emission in both the UV and visible regions. The inclusion of hafnium (Hf) ions in the nodes of the MOF increases the interaction cross-section with ionizing radiation, partially compensating for the low density of the porous material and dramatically increasing the system scintillation yield. The high diffusivity of bimolecular excitons within the framed conjugated ligands allows bimolecular annihilation processes between excited states that partially quench the MOF luminescence, resulting in ultrafast scintillation pulses under X-ray excitation with kinetics in the hundreds of picoseconds time scale. Despite the quenching, the gain in scintillation yield achieved by incorporating Hf ions is large enough to maintain the light yield of the films above 104 ph/MeV under soft X-rays. These unprecedented high efficiencies and simultaneous ultrafast emission kinetics obtained at room temperature in a technologically attractive solid-state configuration, together with the versatility of its composition allowing for further application-specific modifications, place the MOF platform in a prominent position for the realization of the next generation of ultrafast scintillation counters for high-energy physics studies and medical imaging applications.

cond-mat.mtrl-sci↗

arXiv2024

On the origin of the light yield enhancement in polymeric composite scintillators loaded with dense nanoparticles

Fast emitting polymeric scintillators are requested in advanced applications where high-speed detectors with large signal-to-noise ratio are needed. However, their low density implies a weak stopping power of high energy radiations, thus a limited light output and sensitivity. To enhance their performances, polymeric scintillators can be loaded with dense nanoparticles (NPs). We investigate the properties of a series of polymeric scintillators by means of photoluminescence and scintillation spectroscopy, comparing standard scintillators with a composite system loaded with dense hafnium dioxide (HfO2) NPs. The nanocomposite shows a scintillation yield enhancement of +100% with unchanged time response. We provide for the first time an interpretation of this effect, pointing out the local effect of NPs in the generation of emissive states upon interaction with the ionizing radiation. The obtained results indicate that coupling of fast conjugated emitters with optically inert dense NPs could allow to surpass the actual limits of pure polymeric scintillators.

physics.ins-det↗

arXiv2024

Scintillation Properties of CsPbBr3 Nanocrystals Prepared by Ligand-Assisted Reprecipitation and Dual Effect of Polyacrylate Encapsulation toward Scalable Ultrafast Radiation Detectors

Lead halide perovskite nanocrystals (LHP-NCs) embedded in polymeric hosts are gaining attention as scalable and low-cost scintillation detectors for technologically relevant applications. Despite rapid progress, little is currently known about the scintillation properties and stability of LHP-NCs prepared by the ligand assisted reprecipitation (LARP) method, which allows mass scalability at room temperature unmatched by any other type of nanostructure, and the implications of incorporating LHP-NCs into polyacrylate hosts are still largely debated. Here, we show that LARP-synthesized CsPbBr3 NCs are comparable to particles from hot-injection routes and unravel the dual effect of polyacrylate incorporation, where the partial degradation of LHP-NCs luminescence is counterbalanced by the passivation of electron-poor defects by the host acrylic groups. Experiments on NCs with tailored surface defects show that the balance between such antithetical effects of polymer embedding is determined by the surface defect density of the NCs and provide guidelines for further material optimization.

physics.app-ph↗

arXiv2023

Fast emitting nanocomposites for high-resolution ToF-PET imaging based on multicomponent scintillators

Time-of-Flight Positron Emission Tomography is a medical imaging technique, based on the detection of two back-to-back {\gamma}-photons generated from radiotracers injected in the body. Its limit is the ability of employed scintillation detectors to discriminate in time the arrival of {\gamma}-pairs, i.e. the coincidence time resolution (CTR). A CTR < 50 ps that would enable fast imaging with ultralow radiotracer dose. Monolithic materials do not have simultaneously the required high light output and fast emission characteristics, thus the concept of scintillating heterostructure is proposed, where the device is made of a dense scintillator coupled to a fast-emitting light material. Here we present a composite polymeric scintillator, whose density has been increased upon addition of hafnium oxide nanoparticles. This enhanced by +300% its scintillation yield, surpassing commercial plastic scintillators. The nanocomposite is coupled to bismuth germanate oxide (BGO) realizing a multilayer scintillator. We observed the energy sharing between its components, which activate the nanocomposite fast emission enabling a net CTR improvement of 25% with respect to monolithic BGO. These results demonstrate that a controlled loading with dense nanomaterials is an excellent strategy to enhance the performance of polymeric scintillators for their use in advanced radiation detection and imaging technologies.

physics.ins-det↗

arXiv2022

Diffusion-free photon upconversion driven by intramolecular triplet-triplet annihilation in engineered conjugated chromophores

The photon upconversion based on sensitized triplet-triplet annihilation (sTTA-UC) is a spin-flip mechanism exploited to recover the energy of dark triplet states in conjugated systems. In this process a high-energy fluorescent singlet is created through the collision and fusion of two low-energy triplets belonging to different diffusing molecules. Its excellent yield in solution under low excitation intensity and non-coherent light highlighted the huge potential of sTTA-UC to provide a breakthrough in solar technologies. However, its diffusion-limited bi-molecular nature limits its efficiency in the solid state. To overcome this issue, we designed a molecular systems able to host simultaneously more than one triplet, thus enabling a diffusion-free intramolecular TTA. We obtain the first direct demonstration of intramolecular triplet fusion by tailored photoluminescence spectroscopy experiments, thus opening the way to realize a new family of single molecule upconverters with huge potential in solar and lightening technologies by accessing the natural triplets energy reservoir.

cond-mat.mtrl-sci↗

arXiv2020

High Photon Upconversion Efficiency with Hybrid Triplet Sensitizers by Ultrafast Hole-Routing in Electronic-Doped Nanocrystals

Low power photon upconversion (UC) based on sensitized triplet-triplet annihilation (sTTA) is considered as the most promising upwards wavelength-shifting technique to enhance the light harvesting capability of solar devices by recovering the low-energy tail of the solar spectrum. Semiconductor nanocrystals (NCs) with conjugated organic ligands have been proposed as broadband sensitizers for extending the light-harvesting capability of sTTA-UC molecular absorbers. Key to their functioning is efficient energy transfer (ET) from the NC to the triplet state of the ligands that sensitizes the triplet state of free emitters, whose annihilation generates the upconverted emission. To date, the triplet sensitization efficiency in such systems is limited by parasitic processes, such as charge transfer (typically of the photohole) to the organic ligand due to the disadvantageous band alignment of typical NCs and organic moieties. Available strategies only partially mitigate such losses and intrinsically limit the ET yield. Here we demonstrate a new exciton-manipulation approach that enables loss-free ET without detrimental side-effects. Specifically, we use CdSe NCs doped with gold atoms featuring a hole-accepting state in the NC bandgap at a higher energy than the HOMO level of the ligand 9-anthracene acid. Upon photoexcitation, the NC photoholes are routed to the Au-state faster than their transfer to the ligand, producing a long-lived bound exciton in perfect resonance with its triplet state. This hinders hole-transfer losses and results in ~100% efficient ET, over 50-fold higher than in standard NCs. By combining our hybrid sensitizers with an annihilator moiety, we achieved an sTTA-UC efficiency of ~12% (~24% in the normalized definition), which is the highest value for hybrid upconverters based on sTTA reported to date and approaches optimized organic systems.

physics.app-ph↗