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The properties of various inorganic scintillator materials with different origin of their VUV luminescence have been studied under pulsed excitation by XUV (50-1000 eV) synchrotron radiation. A comparison of spectral and timing characteristics of these crystalline VUV emitters has been performed. The processes of energy transfer from the host crystal to the luminescence centers of different nature were analyzed from the features of excitation spectra in the regions of inner-shell absorption. Index Terms--Crossluminescence, excitous, fast VUV luminescence, inorganic scintillators, rare earth ions, synchrotron radiation.

Excitation spectra of Ca[F.sub.2], Sr[F.sub.2] and Ba[F.sub.2] crystals doped by Cd[F.sub.2], La[F.sub.3], Y[F.sub.3] in vacuum ultraviolet region were investigated at liquid-helium temperature and at room temperature. Spectra of doped Ba[F.sub.2] at low temperature and Ca[F.sub.2], Sr[F.sub.2] at room temperature show significant decrease of excitation intensity against those in undoped crystals while the intensifies in exciton regions remain nearly the same. The common reason of the suppression of exciton emission by impurity in alkaline-earth fluorides is unradiative electron-hole recombination on impurity sites. Index Terms--Excitons, impurity, suppression, vacuum ultraviolet.

Commonly used biological indicators for assessing the efficiency of decontamination procedures include the spores of Bacillus atrophaeus (BA) and Geobacillus stearothermophilus (GS). BA and GS spores emit tryptophan-like fluorescence around 320 nm when excited by 280 nm UV light. This fluorescence signal is highly dependent on vaporised hydrogen peroxide (VHP) concentration around the spores, since VHP quenches the fluorescence. In this study we investigated the precise influence of VHP concentration on the autofluorescence properties of BA and GS spores. For both types of spores, the fluorescence signal intensity was found to fall faster and to a relatively lower level when higher VHP concentration was applied. The shape of the signal fall-off as a function of time was found to be well approximated by biexponential decay functions with similar time-constants for BA and GS spores, finally resulting in the equilibrium (or plateau/residual) fluorescence intensity levels that were very different for these samples. The reasons for the fluorescence signal fall-off were investigated by spectral fluorescence signatures (SFS) of the spores. The SFS measurements of the spores during VHP decontamination revealed that the spectral maximum of tryptophan-like (Trp-like) fluorescence changes towards a smaller Stokes shift and has the intensity fall-off due to quenching and oxidation under VHP influence. [ABSTRACT FROM AUTHOR]

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A series of fluorochlorozirconate glasses doped with manganese ions is synthesized and investigated as possible red‐emitting phosphors in comparison with conventional green‐emitting fluorozirconate glasses doped with Mn2+. It is found that the replacement of fluorine by chlorine ions results in broadening and a long‐wavelength shift of the manganese luminescence band into the red region (peaked at 615 nm) although the emission spectrum still has some contribution of the green sub‐band. It turns out also that decay kinetics of luminescence from fluorochlorozirconate glasses becomes nonexponential in contrast to single‐exponential decay observed for green luminescence from Mn2+‐doped fluorozirconate glasses. The observation of two emission components in the luminescence spectrum of fluorochlorozirconate glasses is interpreted as being due to the presence of two Mn2+ emission centers in different local environments. The presence of 2+ valence states of manganese ions in both types of glasses is confirmed by recording X‐ray absorption near edge structure (XANES) spectra at Mn L2,3 edge. Substitution of F− by Cl− ions in anion sites neighboring to Mn2+, leads to a significant rearrangement of the local environment of Mn2+ ions, which results in the long‐wavelength shift of Mn2+ emission spectrum. [ABSTRACT FROM AUTHOR]

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 MAX IV 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 N2 and thiophene (C4H4S) molecules have demonstrated that the setup can be used for many‐particle coincidence spectroscopy. The measurements of the Ar 3p 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 L2,3‐absorption edges in the same experimental session is also demonstrated. Because the photon energy range of the FinEstBeAMS beamline extends from 4.4 eV up to 1000 eV, electron, ion and coincidence spectroscopy studies can be executed in a very broad photon energy range. [ABSTRACT FROM AUTHOR]

Scintillators with ultrafast response are of demand in medical imaging for time-of-flight positron emission tomography, in high-energy physics calorimetry, and in other applications. There are several fast luminescence processes in solid-state materials, which could be good candidates for fast timing applications. The development of new ultrafast silicon photomultipliers with increased vacuum-ultraviolet to ultraviolet (VUV-UV) sensitivity has renewed interest to one of those, cross-luminescence (CL), emitted in the VUV-UV region with subnanosecond decay time. Previous investigations have shown that CL is mostly situated in the VUV region in binary K and Ba compounds, but ternary fluorides with a complex valence band structure can provide ultrafast emissions in UV. According to the band structure calculations for K2SiF6, its complex valence band is composed of the F 2p, Si 2s, and Si 2p states. Transitions between the valence subbands and the outermost K 3p core band may extend CL from the VUV-UV to the visible region. This motivated us to perform spectroscopic study of phase-pure K2SiF6 micropowders with a high degree of crystallinity. The stationary (10 keV) and pulsed (100 keV, δ t ≈ 55 ps) electron beams were applied in the studies of relaxation processes of K2SiF6 in the temperature range of 77–300 K. At 300 K, the dynamics of ultrafast processes was studied at the FemtoMAX beamline (MAX IV Lab) providing 10-keV X-ray pulses of 100-fs duration. As a result, we revealed multiple CL bands extending from 9 to 4 eV. A nonexponential decay in the subnanosecond time range was revealed for the CL bands at 4.5 and 5.25 eV under both pulsed electron-beam and X-ray excitations. This opens prospects for a band structure engineering approach in developing new ultrafast scintillators with intrinsic emissions. This approach is based on a targeted modification of material composition to influence the density of states in complex valence bands and to provide a favorable shift of CL to lower energies. [ABSTRACT FROM AUTHOR]

Single-phase ceramic samples of silicate apatites M2Ln8(SiO4)6O2 (M = Mg, Ca, Sr; Ln = Y, La) undoped and doped with Eu3+, Ce3+, or Mn2+ ions were obtained by the high-temperature solid-state reaction technique using precursors synthesized under hydrothermal conditions. The phosphors were characterized by XRD analysis, Raman spectroscopy, and steady-state/timeresolved and site-selective photoluminescence spectroscopy under blue-to-VUV excitation. It is shown that the small-radius Mg2+ ions, which can occupy two types of suitable sites in the apatite structure, strongly influence luminescence properties of apatites, in particular the distribution of Eu3+ ions between these sites. A bright broad-band yellow emission (peaked at 560 nm with τ 1 µs) was obtained from the Mg2La8(SiO4)6O2:Eu apatite after annealing it in a H2(15%)/Ar reducing atmosphere. This emission is due to 5d-4f transitions of Eu2+ and is efficiently excited by near UV-to-blue light (300-450 nm). Silicate apatites co-doped with optimal concentrations of Eu3+/Eu2+ or Eu2+/Mn2+ can be considered as possible single-phase phosphors for application in warm white pc-LEDs. [ABSTRACT FROM AUTHOR]

The analytical expressions for the three-dimensional spatial distribution of excitons and luminescence decay kinetics of wide band-gap crystals were derived taking into account the saturation effect for absorption near the centre of the incident laser beam with Gaussian transversal profile. The model is verified for the excitonic emission of CdWO crystals under excitation by ultra-short laser pulses in the region of weak excitonic absorption. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structures of the distrontium magnesium disilicate (Sr2MgSi2O7(:Eu2+)) materials were studied by a combined experimental and theoretical approach. The UV–VUV synchrotron radiation was applied in the experimental study while the electronic structures were investigated theoretically by using the density functional theory. The structure of the valence and conduction bands and the band gap energy of the material as well as the position of the Eu2+ 4f ground state were calculated. The calculated band gap energy (6.7eV) agrees well with the experimental value of 7.1eV. The valence band consists mainly of the oxygen states and the bottom of the conduction band of the Sr states. The calculated occupied 4f ground state of Eu2+ lies in the energy gap of the host though the position depends strongly on the Coulomb repulsion strength. The position of the 4f ground state with respect to the valence and conduction bands is discussed using the theoretical and experimental evidence available. [Copyright &y& Elsevier]

Reflection, photo- and cathodoluminescence of 12CaO · 7Al2O3 (C12A7) were investigated. Smooth features observed in VUV reflection spectrum of monocrystalline C12A7 evidence its complicated crystalline structure and lattice disorder. Two luminescence bands peaking at 4.9 and 3.35 eV were revealed in C12A7 ceramics having encaged electrons and O2− ions. The 4.9 eV emission has an excitation onset at 6.8 eV, i.e. near the threshold of free electron-hole pair creation, and is assigned to the recombination of encaged electrons with valence band holes. The 3.35 eV emission is ascribed to the recombination of electrons with the holes localized at the encaged O2− ions. [ABSTRACT FROM AUTHOR]

Abstract: Emission, excitation and absorption spectra of HfO2 and ZrO2 thin films grown by atomic layer deposition were investigated in the temperature range of 10-300K. Time-resolved luminescence spectra were excited with a pulsed ArF laser and tuneable synchrotron radiation in UV–VUV. The strong emission with the peak position at 4.2–4.4eV and with the decay time in μs range was revealed at 10K in both materials. The emission was ascribed to the radiative decay of self-trapped excitons (STE). the features observed in the absorption and excitation spectra at 5.8 and 5.4eV were most probably due to the formation of excitons; While the interband transitions started to dominate at 6.15 and 5.85ev in HfO2 and ZrO2, respectively. [Copyright &y& Elsevier]