The world of luminescent materials offers a stimulating roundtable for the scientific community on the principal factors that drive the luminescence in inorganic bulk and nano-materials. Especially in nanomaterials the promotion of a deep knowledge of defects and of engineering strategies are powerful tools to adapt their electronic and luminescent properties for various applications. We present successful results obtained for nanometric ZnO and HfO2. Their luminescence displays a dependence on the material intrinsic defectiveness. Indeed, we proved that ZnO and HfO2 luminescence features, originating from different optically active defects, are controlled by synthesis and thermo-chemical treatments that lead to morphological modifications, surface/interface restructuring, size change, and thus to rearrangement of defects. In addition, we explore the influence exerted by defectiveness on ZnO photochemical activities and on the generation of persistent toxic free radicals; in parallel we investigate the suitability of a HfO2 blue luminescence emission for future purposes in the scintillation detectors field, as well as in X‐ray triggered oncological therapies.

MgF2 is of interest as a host for Th nuclei in nuclear clock applications. The talk will describe recent modelling work on this material, and a comparison with recently published DFT calculations.

Although it is at first sight a fairly simple material, deriving a potential that fits the structure and gives sensible defect energies was challenging, and the process will be described. Then the calculated intrinsic defect formation energies will be presented.

If Th is to be incorporated in the lattice, it can either substitute for a Mg ion or occupy an interstitial site, both possibilities requiring charge compensation. Solution energies for these processes will be calculated, and the resulting predictions compared with those of a recent published DFT study. A general discussion will be made of how results from the two approaches can be compared and evaluated.

Electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) provide detailed information on the nearest environment of paramagnetic ions through symmetry and hyperfine interactions. They are thus perfectly suited for determining the location of paramagnetic states of transition metal and lanthanide ions in insulating materials.

In recent years our EPR and ENDOR research has mainly focused on understanding how metal dopant ions get incorporated in metal organic frameworks (MOFs). These crystalline, highly porous materials, consisting of metal-inorganic nodes connected by organic struts, have a wide range of potential applications, e.g. in gas storage, separation, sensing and heterogeneous catalysis. Combining various metals in the same framework may lead to new or improved functionality, or allow to build in an metal ion with desired properties in an inert and highly stable host. The rationale behind doping of MOFs is thus similar as for classical oxide and halide materials.

MOFs are most often synthesized via solvothermal methods. Metal doping occurs by adding dopants to the solution during synthesis or via post-synthesis ion exchange reactions in solution. These procedures do not necessarily only lead to simple metal substitution. In this presentation, we illustrate this with our recent work on vanadium doping of a (Al-OH)-biphenyl-dicarboxylate MOF (DUT-5), where we combine EPR and ENDOR with infrared spectroscopy, X-ray diffraction and electron microscopy.

¹ Department of Physics, Osnabrück University, 49076 Osnabrück, Germany (, , )

² Center for Cellular Nanoanalytics, Osnabrück University, 49076 Osnabrück, Germany

³ Department of Biology/Chemistry, Osnabrück University, 49076 Osnabrück, Germany (, , )

Niobate nanocrystals are increasingly used as imaging markers in nanobiophotonics. The basic principle is based on the frequency conversion of intense IR light, so that harmonic light in the visible spectral range is emitted by the crystals having diameters in the sub-100 nm range.

The use of niobate nanocrystals has a number of advantageous features compared to molecular fluorescence markers or quantum dots, such as the generation of coherent light radiation, without blinking or bleaching and the ability to generate light in a very wide spectral range. This allows novel imaging techniques, or at least marker-based imaging for those cases where established fluorescent markers fail.

However, the potential of niobate nanocrystals goes far beyond the pure application in imaging. In particular, the possibility of doping with rare earth elements and the advanced crystal physical properties, such as pyroelectricity and piezoelectricity, opens up a broad field of novel applications in light-based manipulation of physiological environments. A particularly great advantage is the comprehensive know-how gained over several decades in volume single crystals, which provides an outstanding basis for the study and application of niobate nanocrystals. Despite of this, applications of niobate nanocrystals in the so-called optogenetics field has been scarce so far.

The lecture will first present the current status of the use of niobate nanocrystals. Using KNbO3 as an example, the current approaches to the synthesis of niobate nanocrystals (bottom-up by hydrothermal or solvothermal synthesis vs. top-down by ball milling and etching processes) are summarised and the structural and optical properties are compared with volume single crystals by means of structure elucidation, electron microscopy and spectroscopy. The study of the nonlinear optical properties is performed by means of diffuse reflectance spectroscopy, which allows to derive the optimal laser system parameters for imaging in a laser-pumped nonlinear optical microscope. By matching the pulse repetition rate, average power and photon energy with the absorption spectrum of a Drosophila larva, it is possible to detect the niobate nanocrystals in the heart system of a living Drosophila and thus determine the hemolymph circulation, velocity or flow properties experimentally.

The microscopy system developed especially for these experiments also enables non-linear optical confocal laser microscopy and illumination with several laser pulses of different photon energies, both simultaneous and time-shifted. These properties form the prerequisites for the further study of doped niobate nanocrystals, which will be discussed. Of particular interest are Fe doping, which is associated with the occurrence of the volume photovoltaic effect in Fe-doped KNbO3, or doping with Er or Yb, so that a coupling of frequency conversion processes with luminescence becomes conceivable.

Pulse-induced photoluminescence (PL) and transient absorption (TA) experiments in LiNbO₃, in particular their timescales ranging from nanoseconds to minutes in the ultraviolet/visible/ near-infrared region, have been interpreted, as a rule, separately: PL mostly by the generation, transport and recombination of self-trapped excitons, and TA by small polarons with strong coupling. However, the possible interplay between the different species, and the simultaneous presence of parallel radiative and non-radiative decay channels, affecting both PL and TA have been given insufficient consideration, so far.

These shortcomings can be eliminated by systematically using a model of coupled processes with differently time-dependent decay kinetics, and by taking into account, in addition to charged polaronic and dipolar excitonic states, also variously formed pinned excitonic states localized next to dipolar defect complexes¹. Exorbitantly long lifetimes of PL and TA components in doped systems can be explained by excitons pinned on charge compensated dopant ions, while nanosecond-scale PL lifetimes in undoped congruent LiNbO₃ can be attributed to excitons trapped on complexes containing Nb_Li antisites. The role of hopping polarons is limited to causing the ‘regular’ microsecond-scale TA component and yielding an alternative path for the formation of long-lived pinned-excitonic states active in long PL and long TA.

We discuss the validity of the proposed models and scenarios for the treatment of stretched exponential or other time-dependent kinetics in other cases, including complex condensed systems ranging from nanocrystals and polymers to liquids and biophysical systems.

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¹G. Corradi, A. Krampf, S. Messerschmidt, L. Vittadello, M. Imlau, J. Phys. Condens. Matter 32, 413005 (2020)

Insulating oxide epitaxial nanostructures produced by laser molecular beam epitaxy (LMBE) technique can be promising candidates for realizing beyond state of the art devices.

Cr³⁺ and Eu³⁺ ions doped MgO, MgAl₂O₄ and Y₂O₃ films (5–200 nm) were grown on different substrates with the use of LMBE system based on KrF excimer laser.

The fluorescence spectra of MgO:Cr³⁺ films revealed strong inhomogeneous broadening. It is shown that in such situation the measurements of the ²E state radiative lifetimes may be used for diagnostics of lattice distortions in epitaxial films. [1]

The spectra of MgAl₂O₄:Cr³⁺ films reflect Al/Mg inversion in the lattice. The possibility to obtain normal (non-inversed) spinel films is discussed. [2]

In Y₂O₃:Eu³⁺ films the variations of the radiative lifetimes of Eu^{3+ 5}D₀ level with the index of refraction of the medium surrounding the sample were observed. The effect was explained by the local field and photon density of states modification due to the nearby interfaces.

[1] S.P. Feofilov, A.B. Kulinkin, A.K. Kaveev, N.S. Sokolov, S.M. Suturin. Opt. Mat. 83, 43 (2018).

[2] S.P. Feofilov, A.B. Kulinkin, A.K. Kaveev, N.S. Sokolov, S.M. Suturin. Thin Solid Films 693, 137732 (2020).

Luminescence properties of point defects in insulating materials are successfully used for solid state light sources and radiation sensors. The peculiar photoluminescence characteristics of colour centres in lithium fluoride (LiF), well known for applications in optically-pumped tuneable lasers and miniaturized light-emitting photonic devices operating at room-temperature, are exploited in passive ionizing-radiation imaging detectors and dosimeters based on visible radiophotoluminescence in LiF crystals and polycrystalline thin films. Their peculiarities, such as very high intrinsic spatial resolution, wide dynamic range and large field of view, combined with easy handling, ambient-light operation and no development need, allow to successfully extend their use from X-ray imaging to proton beam advanced diagnostics and dosimetry, even at dose values that are typical of hadrotherapy. A review of the properties of LiF-based detectors and dosimeters is presented together with the main results, with the aim to discuss challenges related to control the radiophotoluminescence response in both bulk and thin film forms.

Sirius, the new Brazilian Synchrotron Light Source, is the largest and most complex scientific infrastructure ever built in Brazil. It is one of the world’s first fourth-generation synchrotron light sources, comparable only to MAX IV in Sweden and the recently upgraded European Synchrotron Radiation Facility (ESRF-EBS) situated in Grenoble, France. The design and construction principles of this new Brazilian 3 GeV light source were envisaged to optimize production and use of coherent x-rays, with in-house developments ranging from the multi-bend magnetic lattice, to high-dynamic active feedback opto-mechanical devices, and fast, low-noise area detectors. This new facility will provide cutting edge research tools that are nonexistent today in Brazil and place the country among the world leaders in this type of technology, which allows analysis of synthetic and biological materials in time and length scales unprecedented in the current state of the art. This new tool will leverage the development of research in strategic areas such as energy, food, environment, health, defense and many others. The first 6 beamlines of Sirius are in different stages of construction/commissioning and the first results obtained in commissioning phase from the MANACÁ (protein crystallography) are already very promising. In this talk I will overview the main characteristics, potentialities, status of the project and the initial results from commissioning.

¹Institute of Physic, UKW in Bydgoszcz, Powstańców Wielkopolskich str., 2, 85-090 Bydgoszcz, Poland

²Institute of Physics, AS of Czech Republic, Cukrovarnicka str., 10, 16253 Prague, Czech Republic

³Institute for Scintillation Materials, NAS of Ukraine, av. Nauky, 60, 61001 Kharkiv, Ukraine

⁴Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan

This report presents the latest results in the development of multilayer composite scintillators of phoswich-type (phosphor sandwich) based on single crystalline films (SCF) and single crystals (SC) of garnet compounds using the liquid-phase epitaxy (LPE) growth method for application in environment radiation monitoring for simultaneous registration of different types of ionizing radiation (particles and quanta) in mixed ionization fluxes [1-5], as well as for scintillating screens in the microimaging technique [6]. Such composite scintillators present the multilayer epitaxial structures containing one or two film scintillators grown „step-by-step” onto substrates from crystal scintillators using the LPE method. Films and crystal parts of the composite scintillators were fabricated from “as best as possible” effective scintillation materials on the basis of Ce³⁺, Pr³⁺ and Sc³⁺ doped Lu₃Al₅O₁₂ garnets [1-3] (case of homoepitaxial growth) and the Ce³⁺ doped R₃B₅O₁₂ (R= Gd, Lu, Tb; B=Al, Ga) mixed garnets [4, 5](case of heteroepitaxial growth) with various scintillation decay kinetics due to the different types of dopants [1-3] and various garnet content [4, 5].

The report presents the results of our latest achievement on fabrication of new two-layered composite scintillators of Gd₃A_3.85-2.35Ga_1.15-2.65O₁₂:Ce SCF/Gd₃Al_3-2.5Ga_2.5O₁₂:Ce SC and TbAG:Ce SCF/Gd₃Al_2.3-2Ga_2.7-3O₁₂:Ce SC types as well as the advanced three-layered YAG:Ce SCF/LuAG:Pr SCF/LuAG:Sc SC, YAG:Ce SCF/TbAG:Ce SCF/Gd₃Al_2.5Ga_2.5O₁₂:Ce SC and TbAG:Ce SCF/ Gd₃Al_3-2.5Ga_2-2.5O₁₂:Ce SCF/Gd₃Al₂Ga₃O₁₂:Ce SC composite scintillators based on the crystals and films of the above mentioned garnet compounds by the LPE growth method.

The results of investigation of their luminescent and scintillation properties were presented as well. The testing of the mentioned prototypes of two- and three-layered composite scintillators for simultaneous registration of α- and β- particles and γ-quanta was performed and the obtained results were analysed for the optimization of their composition and a figure-of merit of scintillation.

References

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[2] S. Witkiewicz-Lukaszek, V. Gorbenko, T. Zorenko, K. Paprocki, O. Sidletski, I. Gerasymov, J.A.Mares, R. Kucerkova, M. Nikl, Yu. Zorenko, Optical Materials, 2018, 84, 593-599.

[3] J.A. Mares, S. Witkiewicz-Lukaszek, V. Gorbenko, T. Zorenko, R. Kucerkova, A. Beitlerova, C. D′Ambrosio, J. Dlouhy, M. Nikl, Yu Zorenko, Optical Materials, 2019, 96, 109268

[3] S. Witkiewicz-Lukaszek, V. Gorbenko, T. Zorenko, O. Sidletskiy, I. Gerasymov, A. Fedorov, A. Yoshikawa, J. A. Mares, M. Nikl, and Yu. Zorenko, Crystal Growth & Design 2018, 18, 842.

[4] S. Witkiewicz-Lukaszek, V. Gorbenko, T. Zorenko, K. Paprocki, O. Sidletskiy, A. Fedorov, J.A. Mares, R. Kucerkova, M. Nikl, Yu. Zorenko. CrystEngComm, 2018, 20, 3994-4002.

[5] S. Witkiewicz-Lukaszek, V. Gorbenko, T. Zorenko, O. Sidletskiy, P. Arhipov, A. Fedorov, J.A. Mares, R. Kucerkova, M. Nikl, Yu. Zorenko, CrystEngComm, 2020, 22, 3713-3724

[6] Yu. Zorenko, P.-A. Douissard, T. Martin, F. Riva, V. Gorbenko, T. Zorenko, K. Paprocki, A. Iskalieva, S. Witkiewicz, A. Fedorov, P. Bilski, A. Twardak, Optical Materials, 2017, 65, 73.

Acknowledgements: The work was supported by Polish NCN 2018/31/B/ST8/03390 project, Czech National Foundation 16-15569S project and Japanese 2018SV11 ICC-IMR Tohoku University project.