Phase transition, radio- and photoluminescence of K3Lu(PO4)2 doped with Pr3+ ions

Luminescent characteristics of K3Lu(PO4)2:Pr3+ (1 and 5 mol.%) microcrystalline powders, a promising optical material for scintillation applications, were investigated using various experimental techniques. The material shows emission features connected with both high intensity interconfigurational 4f15d→4f2 transitions (broad UV emission bands) and intraconfigurational 4f2→4f2 transitions (weak emission lines in the visible range). The output of X-ray excited 4f15d→4f2 emission of Pr3+ increases with a temperature rise from 90 K to room tem- perature and higher depending on the Pr3+ ions concentration. The high 5% concentration of Pr3+ ions is found to be favourable for the stabilization of a monoclinic phase (P21/m space group) over a trigonal one (P3 space group) while emission properties of the material reveal that a phase transition occurs at higher temperatures. Decay kinetics of Pr3+ 4f15d→4f2 emission are recorded upon excitation with high repetition rate X-ray syn- chrotron excitation and pulse cathode ray excitation. Issues related to a non-exponential decay of luminescence and presence of slow decay components are discussed in terms of energy transfer dynamics. The presence of defects was revealed with thermoluminescence measurements and these are suggested to be the mainly responsible for delayed recombination of charge carriers on the Pr3+ 4f15d states. Some peculiarities of host-to- impurity energy transfer are discusse

Real-time monitoring of hydrogen peroxide vapour decontamination of bacterial spores by means of UV fluorimetry

This study is devoted to the development of a UV fluorimetry sensor capable of real-time monitoring of the decontamination process of microbiological pathogens by hydrogen peroxide vapour (HPV) treatment. The sensor is operating on the autofluorescence signal of tryptophan. The Bacillus atrophaeus (B. atrophaeus) and Geobacillus stearothermophilus (G. stearothermophilus) spores were exposed to HPV and the resulting dynamic change in tryptophan fluorescence intensity as a function of time was recorded and analysed. It was revealed that the introduced HPV atmosphere caused a 4-time decrease in the fluorescence intensity of the tryptophan emission due to the interaction of HPV with the spores. It was shown that achieving a persistent minimal level of the autofluorescence signal due to the microorganism-bound tryptophan during the defined time period is well correlated with the efficiency of the ongoing decontamination process in the HPV treatment course. Therefore, the progress of the HPV decontamination procedure can be firmly evaluated, using fluorescence data obtained in real time and the validity of the method was demonstrated by comparing the fluorescence data with the reference information obtained by implementing classical microbiology viability tests (incl. time behaviour) for various microorganisms in the HPV atmosphere

Gas-phase endstation of electron, ion and coincidence spectroscopies for diluted samples at the FinEstBeAMS beamline of the MAXIV 1.5GeV storage ring

Since spring 2019 an experimental setup consisting of an electron spectrometer and an ion time-of-flight mass spectrometer for diluted samples has been available for users at the FinEstBeAMS beamline of the MAXIV Laboratory in Lund, Sweden. The setup enables users to study the interaction of atoms, molecules, (molecular) microclusters and nanoparticles with short-wavelength (vacuum ultraviolet and X-ray) synchrotron radiation and to follow the electron and nuclear dynamics induced by this interaction. Test measurements of N-2 and thiophene (C4H4S) molecules have demonstrated that the setup can be used for many-particle coincidence spectroscopy. The measurements of the Ar3p photoelectron spectra by linear horizontal and vertical polarization show that angle-resolved experiments can also be performed. The possibility to compare the electron spectroscopic results of diluted samples with solid targets in the case of Co2O3 and Fe2O3 at the Co and Fe L-2,L-3-absorption edges in the same experimental session is also demonstrated. Because the photon energy range of the FinEstBeAMS beamline extends from 4.4eV up to 1000eV, electron, ion and coincidence spectroscopy studies can be executed in a very broad photon energy range

Relaxation of intrinsic and extrinsic electronic excitations in nano- and micro-size alumina

Nanopowders consisting of mixed α-alumina and transition alumina phases were prepared by combustion synthesis and investigated using low temperature time-resolved cathodoluminescence and photoluminescence spectroscopy under VUV excitation. The onsets of the intrinsic absorption for different alumina phases were revealed in mixed phase nanopowders by analysing luminescence excitation spectra. All synthesized nanopowders possessed the intrinsic luminescence band with a maximum at 4.6 eV, which is assigned to the radiative decay of triplet self-trapped excitons with ∼750 μs decay time at 78 K. A red shift by 0.3 eV was revealed for the peak of the O$^{2−}$ – Cr$^{3+}$ charge transfer band near 7 eV as a function of particle size. This shift is correlated with the decrease of α-alumina particle size from 180 to 80 nm. Its origin is discussed in the framework of the Kroning-Penney model

Investigation of luminescence processes in YAG single crystals irradiated by 50 MeV electron beam

Absorption, emission and excitation spectra of 50 MeV electron beam irradiated and as-grown YAG single crystals were studied and compared in the 10–300 K temperature range using time-resolved luminescence spectroscopy under UV/VUV/XUV excitation by synchrotron radiation and cathodoluminescence. The emission spectra consist of intrinsic (excitonic) and defect related non-elementary bands in the VIS/UV range. It is shown that fast electrons create stable F and F+ color centers with characteristic emission and absorption bands in the visible/UV range. Induced absorption caused from these defects starts at 4.2 eV. Energy transfer from host to color centers is not an efficient process

Efficient and stable photocatalyst for photoelectrochemical splitting of water

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