Kateřina Děcká

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.

Nanorods of erbium-doped zinc oxide (ZnO:Er) were fabricated using a hydrothermal method. One batch was prepared with and another one without constant ultraviolet (UV) irradiation applied during the growth. The nanorods were free-standing (FS) as well as deposited onto a fused silica glass substrate (GS). The goal was to study the atomistic aspects influencing the charge transport of ZnO nanoparticles, especially considering the differences between the FS and GS samples. We focused on the excitons; the intrinsic defects, such as zinc interstitials, zinc vacancies, and related shallow donors; and the conduction electrons. UV irradiation was applied for the first time during the ZnO:Er nanorod growth. This led to almost total exciton and zinc vacancy luminescence reduction, and the number of shallow donors was strongly suppressed in the GS samples. The effect was much less pronounced in the FS rods. Moreover, the exciton emission remained unchanged there. At the same time, the Er³⁺ content was decreased in the FS particles grown under constant UV irradiation while Er³⁺ was not detected in the GS particles at all. These phenomena are explained.

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.

Cationic doping of ZnO nanorods has gained increased interest as it can lead to the production of materials with improved luminescent properties, electrical conductivity and stability. We report on various Mo-doped ZnO powders of nanorods synthesized by the hydrothermal growth method. Further annealing or/and cold hydrogen or oxygen plasma modification was applied. The atomic structure of the as-grown and plasma-modified rods was characterized by X-ray diffraction. To identify any possible changes in morphology, scanning electron microscopy was used. Paramagnetic point defects were investigated by electron paramagnetic resonance. In particular, two new types of defects were initiated by the plasma treatment. Their appearance was explained, and corresponding mechanisms were proposed. The changes in the luminescence and scintillation properties were characterized by photo- and radioluminescence, respectively. Charge trapping phenomena were studied by thermally stimulated luminescence. Cold plasma treatment influenced the luminescence properties of ZnO:Mo structures. The contact with hydrogen lead to an approximately threefold increase in intensity of the ultraviolet exciton-related band peaking at ~3.24 eV, whereas the red band attributed to zinc vacancies (~1.97 eV) was suppressed compared to the as-grown samples. The exciton- and defect-related emission subsided after the treatment in oxygen 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.