Václav Čuba

CsPbBr₃ nanocomposites are prospective luminescent materials with great potential for many light-emitting applications. However, embedding CsPbBr₃ nanocrystals into some potentially interesting matrices proves challenging in terms of maintaining their properties and good transparency of the final nanocomposite, e.g., high temperature polymerization of widely used and radiation-hard polystyrene or employment of more polar polymers such as polyurethanes often leads to nanocrystal degradation. Here, we present a functionalization strategy using ammonium hexafluorosilicate in combination with functional organosilanes for the fabrication of CsPbBr₃ nanocomposites, which provides improved thermal stability of surface passivation up to 110 °C. Moreover, it enables for the first time concomitant surface modification to enhance compatibility between nanocrystals and the matrix, leading to improved transparency of nanocomposites. We demonstrate that the process can be tailored by preparing polystyrene (PS) and polyurethane (PU) nanocomposites. This opens the way for easier processability of popular high cure temperature polymers such as polystyrene, as well as for efficient embedding of NCs into novel matrices with the aim of exploiting crucial properties for desired applications, for example, radiation hardness or flexibility.

Cesium lead halide nanocrystals (NCs) and their nanocomposites have attracted a lot of attention in the field of radiation detection thanks to their excellent luminescent properties, especially their potential for fast timing. However, most research on their nanocomposites focuses on low loadings (around 1 wt%) which is insufficient for detecting high-energy X-rays or γ-rays. There have been only few reports exploring materials with higher loadings but all with limited success in terms of transparency of the final material. In our work, we present nanocomposites of cesium lead halide NCs with loading up to 40 wt%. We employ innovative surface functionalization of the NCs to enhance their dispersion within the matrix, thereby improving the final material transparency. We display the NC dispersion within the matrix using confocal photoluminescence microscopy and we then characterise the radioluminescent properties of nanocomposites of cesium lead bromide (CPB) and cesium lead bromochloride NCs with varying chloride content. To asses their performance as radiation detectors, we measure their timing capabilities under X-rays. Our findings reveal a significant improvement in time resolution under X-rays from previously published 300 ps for CPB polymer nanocomposites to 215 ps. When combined with increased stopping power of high NC content, this advancement holds great promise for practical applications, e.g. in time-of-flight positron emission tomography and computed tomography or high energy physics.

Time‐of‐flight (TOF) technique, traditionally used in high energy physics (HEP) and positron emission tomography (PET), is now being explored for lower energy applications like computed tomography (CT). Regardless of the application, pushing the current boundaries in time resolution calls for novel technologies and materials exhibiting ultra‐fast time response. Semiconductor nanocrystals like cesium lead halide perovskites (CsPbBr₃), benefiting from quantum confinement effects, feature ultra‐fast decay and, when combined with a suitable bulk scintillator following a heterostructure concept, can also provide the necessary stopping power. In this work, thin films of CsPbBr₃ on top of BGO, LYSO:Ce, and GAGG:Ce,Mg wafers are fabricated to test their impact on the single crystal scintillator time resolution under soft X‐rays excitation (about 10 keV). It is demonstrated that the CsPbBr₃ layer significantly improves the overall time resolution in all cases, achieving up to a tenfold improvement with BGO and GAGG:Ce,Mg. Under 511 keV γ‐rays, a proof‐of‐concept of the heterostructure design for TOF‐PET using CsPbBr₃ thin film deposited on GAGG:Ce,Mg bulk crystal is successfully tested. Shared events depositing energy in both materials are identified, resulting in more than twofold improved coincidence time resolution: 118 ± 4 ps full‐width‐at‐half‐maximum (FWHM) compared to the 272 ± 8 ps of solely GAGG:Ce,Mg.

For the first time, monoclinic crystalline HfO₂ is achieved by scalable and low-cost photochemical synthesis. This approach is valid for the creation of large area HfO₂-based scintillating composites for fast timing applications.

A combination of synchrotron-based elemental analysis and acute toxicity tests was used to investigate the biodistribution and adverse effects in Daphnia magna exposed to uranium nanoparticle (UNP, 3-5 nm) suspensions or to uranium reference (U_ref) solutions. Speciation analysis revealed similar size distributions between exposures, and toxicity tests showed comparable acute effects (UNP LC₅₀: 402 μg L^-1 [336-484], U_ref LC₅₀: 268 μg L^-1 [229-315]). However, the uranium body burden was 3- to 5-fold greater in UNP-exposed daphnids, and analysis of survival as a function of body burden revealed a ∼5-fold higher specific toxicity from the U_ref exposure. High-resolution X-ray fluorescence elemental maps of intact, whole daphnids from sublethal, acute exposures of both treatments revealed high uranium accumulation onto the gills (epipodites) as well as within the hepatic ceca and the intestinal lumen. Uranium uptake into the hemolymph circulatory system was inferred from signals observed in organs such as the heart and the maxillary gland. The substantial uptake in the maxillary gland and the associated nephridium suggests that these organs play a role in uranium removal from the hemolymph and subsequent excretion. Uranium was also observed associated with the embryos and the remnants of the chorion, suggesting uptake in the offspring. The identification of target organs and tissues is of major importance to the understanding of uranium and UNP toxicity and exposure characterization that should ultimately contribute to reducing uncertainties in related environmental impact and risk assessments.

Nanocrystals of CsPbBr₃ have been incorporated in a polystyrene matrix with 1–10% weight filling factors. Samples were characterized with the main focus on their timing capability under soft X-ray irradiation for application as ultrafast scintillation detectors.

Under controlled laboratory conditions, lasers represent a source of energy with well-defined parameters suitable for mimicking phenomena such as ablation, disintegration, and plasma formation processes that take place during the hypervelocity atmospheric entry of meteoroids. Furthermore, lasers have also been proposed for employment in future space exploration and planetary defense in a wide range of potential applications. This highlights the importance of an experimental investigation of lasers’ interaction with real samples of interplanetary matter: meteorite specimens. We summarize the results of numerous meteorite laser ablation experiments performed by several laser sources—a femtosecond Ti:Sapphire laser, the multislab ceramic Yb:YAG Bivoj laser, and the iodine laser known as PALS (Prague Asterix Laser System). The differences in the ablation spots’ morphology and their dependence on the laser parameters are examined via optical microscopy, scanning electron microscopy, and profilometry in the context of the meteorite properties and the physical characteristics of laser-induced plasma.

In this study, a UV light-based technology for the syntheses of nano-dimensional metal oxides feasible in an industrial scale is proposed, based on our long term experience with the operation of a photochemical pilot plant. We demonstrate the synthesis, properties and manufacturing costs with a case study for ZnO, Y₃Al₅O₁₂ and Gd₃Ga₂Al₃O₁₂ materials that are comparable with laboratory-scale yields and purity. The process relies on irradiation of aqueous solutions containing dissolved precursors, typically formate anions and soluble metal salts, with 254 nm UV light. Depending on the solution composition, UV irradiation leads to the formation of nanocrystalline or amorphous products of particulate or gel-like character. These materials can be either used as is, or further processed, usually by drying in air and heat-treating at elevated temperatures (200–1200 °C), leading to a fine powder suitable for a subsequent use in different applications. A number of syntheses were developed during the past few years to provide an evaluation of various aspects influencing the manufacturing process such as solution composition or character of the product. The observed yields were correlated with both the concentration of the salts in solutions and the irradiation time; then, photochemical production rates were determined, and the potential of this method for up-scaling was evaluated. X-ray diffraction results and radioluminescence measurements prove that the phase purity and emission spectra of the produced materials are fully comparable to those from laboratory-scale preparations. Realistic assumptions and considerations were then used for a comprehensive estimation of manufacturing costs in the described photochemical pilot plant and the parameters leading to lower manufacturing costs were identified.

Lead halide perovskite nanocrystals of the formula CsPbBr₃ have recently been identified as potential time taggers in scintillating heterostructures for time-of-flight positron emission tomography (TOF-PET) imaging thanks to their ultrafast decay kinetics. This study investigates the potential of this material experimentally. We fabricated CsPbBr₃ thin films on scintillating GGAG:Ce (Gd_2.985Ce_0.015Ga_2.7Al_2.3O₁₂) wafer as a model structure for the future sampling detector geometry. We focused this study on the radioluminescence (RL) response of this composite material. We compare the results of two spin-coating methods, namely the static and the dynamic process, for the thin film preparation. We demonstrated enhanced RL intensity of both CsPbBr₃ and GGAG:Ce scintillating constituents of a composite material. This synergic effect arises in both the RL spectra and decays, including decays in the short time window (50 ns). Consequently, this study confirms the applicability of CsPbBr₃ nanocrystals as efficient time taggers for ultrafast timing applications, such as TOF-PET.

CsPbBr₃ nanocrystals have been identified as a highly promising material for various optoelectronic applications. However, they tend to coexist with Cs₄PbBr₆ phase when the reaction conditions are not controlled carefully. It is therefore imperative to understand how the presence of this phase affects the luminescence performance of CsPbBr₃ nanocrystals_. We synthesized a mixed CsPbBr₃-Cs₄PbBr₆ sample, and compared its photo- and radioluminescence properties, including timing characteristics, to the performance of pure CsPbBr₃ nanocrystals. The possibility of energy transfer between the two phases was also explored. We demonstrated that the presence of Cs₄PbBr₆ causes significant drop in radioluminescence intensity of CsPbBr₃ nanocrystals, which can limit possible future applications of Cs₄PbBr₆-CsPbBr₃ mixtures or composites as scintillation detectors.