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Abstract: 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. [Copyright &y& Elsevier]

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]

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]

A complex investigation of the dynamics of electronic excitations in potassium dihydrophosphate (KDP) crystals is performed by the low-temperature time-resolved vacuum ultraviolet optical luminescence spectroscopy with subnanosecond time resolution and with selective photoexcitation by synchrotron radiation. For KDP crystals, data on the kinetics of the photoluminescence (PL) decay, time-resolved PL spectra (2–6.2 eV), and time-resolved excitation PL spectra (4–24 eV) at 10 K were obtained for the first time. The intrinsic character of the PL of KDP in the vicinity of 5.2 eV, which is caused by the radiative annihilation of self-trapped excitons (STEs), is ascertained; σ and π bands in the luminescence spectra of the STEs, which are due to singlet and triplet radiative transitions, are resolved; and the shift of the σ band with respect to the π band in the spectra of the STEs is explained. [Copyright &y& Elsevier]

The VUV luminescence properties of several Ba containing crystals in the temperature range of 10–300 K were investigated using energy- and time-resolved spectroscopy under excitation by XUV photons. The results are compared with those obtained under excitation by photons up to 40 eV. The revealed new emission bands can originate from the radiative recombination of valence electrons with the outermost Ba2+ 5p core holes and from the radiative transitions of multiply charged Ba ions. The possible inter-atomic cross-relaxation of holes from the fluorine to the barium ion in BaF2 was revealed as well. [Copyright &y& Elsevier]

Abstract: Luminescence properties and electronic excitations of δ- and Θ-phases of Al2O3 nano-powders, prepared by plasma processing technique, were studied using time-resolved luminescence spectroscopy under vacuum ultraviolet excitation. The fundamental absorption edge was found at 7.5eV, which is 1.5eV less than that of α-Al2O3 in agreement with theoretical predictions for transition alumina. The broad-band emissions with maxima at 5.5 and 4.6eV are assigned to radiative decay of the intrinsic excitations. Emission of transition metal impurities was found near 1.75eV. The emission bands peaked at 3.1 and 2.6eV are assigned to F+ and F centres, respectively. [Copyright &y& Elsevier]

Abstract FinEstBeAMS is a new materials science beamline at the 1.5 GeV storage ring of the MAX IV Laboratory in Lund, Sweden. It has been built based on grazing incidence monochromatization of synchrotron light, which allows to cover a remarkably wide excitation energy range from ultraviolet to soft x-rays (4.5–1450 eV). A new mobile luminescence spectroscopy end station has been commissioned with design benefitting from the advantages of a high flux elliptically polarizing undulator light source. We report on the design of the luminescence end station, its technical realization and performance achieved so far. Special attention is paid to the experimental challenges for luminescence spectroscopy under grazing incidence excitation conditions. The first luminescence results obtained demonstrate a reliable performance of the advanced setup at FinEstBeAMS. [ABSTRACT FROM AUTHOR]

Abstract: A complex investigation of the dynamics of electronic excitations and luminescence in nonlinear optical crystals of ammonium dihydrophosphate NH4H2PO4 was performed using low-temperature vacuum ultraviolet luminescence spectroscopy with time resolution upon selective photoexcitation by synchrotron radiation. Data on the photoluminescence (PL) decay kinetics, time-resolved PL spectra (2–6.2eV), and time-resolved PL excitation spectra (4–24eV) were obtained for the first time for NH4H2PO4 crystals at 8K. It is ascertained that the PL of NH4H2PO4 crystals in the vicinity of 4.7eV has intrinsic character due to the radiative annihilation of self-trapped excitons. Possible channels of generation and decay of relaxed and unrelaxed electronic excitations in NH4H2PO4 crystals are discussed. [Copyright &y& Elsevier]

Optical absorption and photoluminescence of amorphous and crystalline HfO2 thin films grown by atomic layer deposition from HfCl4 and H2O were studied. Band-gap energy of (5.55±0.03) eV was determined for monoclinic HfO2 with mean crystallite sizes of 30–40 nm as well as for amorphous HfO2. Excitation in the range of intrinsic absorption resulted in emission that had maximum intensity at 3.2 eV in the case of amorphous films and at 2.6 or 4.4 eV in the case of monoclinic films. The emission intensity of crystalline films exceeded that of amorphous films by an order of magnitude at all temperatures studied. The main luminescence band at 4.4 eV was tentatively assigned to the emission of self-trapped excitons while the emission at lower photon energies was attributed to defects and impurities. With the increase of temperature from 10 to 295 K, the low-energy edges of excitation spectra shifted towards lower energies by 0.1 eV in the case of amorphous films and by 0.15 eV in the case of crystalline films, indicating corresponding changes in the band-gap energies. [Copyright &y& Elsevier]

Nanocrystalline gamma alumina (γ-Al 2 O 3 ) powder with a crystallite size of ~10 nm was synthesized by oxidation of high purity aluminium plate in a humid atmosphere followed by annealing in air. Spark plasma sintering (SPS) at different sintering parameters (temperature, dwell time, heating rate, pressure) were studied for this highly porous γ-Al 2 O 3 in correlation with the evolution in microstructure and density of the ceramics. SPS sintering cycles using different heating rates were carried out at 1050–1550 °C with dwell times of 3 min and 20 min under uniaxial pressure of 80 MPa. Alumina sintered at 1550 °C for 20 min reached 99% of the theoretical density and average grain size of 8.5 µm. Significant grain growth was observed in ceramics sintered at temperatures above 1250 °C. [ABSTRACT FROM AUTHOR]

Mixed nanopowders of transition alumina prepared by combustion synthesis and phase pure ultra-porous α-alumina by oxidation method were investigated using low temperature time-resolved cathodoluminescence and photoluminescence spectroscopy under VUV-XUV excitation. In all samples along with the 7.6 eV emission of self-trapped excitons of α-alumina, luminescence bands due to F, F + centres with maxima at 3 and 3.8 eV and other UV–visible luminescence bands of intrinsic and extrinsic origin with varying intensity depending on sample preparation method and thermal treatment were studied. In alumina nanopowders the excitonic excitation peak at ∼9.1 eV near fundamental absorption edge is shifted to the higher energies by 0.15 eV in comparison with the same feature in single crystals. The nanostructure of alumina is responsible for this shift. [ABSTRACT FROM AUTHOR]

Abstract: Luminescence spectroscopy in the VUV-visible range under electron-beam excitation and synchrotron radiation was applied to investigate electronic properties of alumina nanopowders, which were prepared using the combustion synthesis method. By varying reaction and post treatment conditions we were able to prepare phase pure samples and powders with mixtures of α- and γ-phases mainly. In addition to the well-known 7.6 eV luminescence of STE of α-alumina, all samples possessed complex emission bands in UV range (3–5 eV) which originate from intrinsic excitonic emissions and extrinsic electronic excitations. [Copyright &y& Elsevier]

Abstract: We report on observation of upconverted VUV luminescence due to 5d–4f radiative transitions in Er3+ and Nd3+ ions doped into some fluoride crystals, under excitation by ArF and KrF excimer lasers, respectively. Only spin-forbidden 5d–4f luminescence of Er3+ (at 165nm) was detected from the LiYF4:Er3+ crystal whereas both spin-forbidden (at 169nm) and spin-allowed (at 160.5nm) components are observed from the BaY2F8:Er3+ crystal, the latter being much weaker than in the case of one-photon excitation. Nd3+ 5d–4f luminescence at 180 and 173nm has been detected from the LiYF4:Nd3+ and LaF3:Nd3+ crystals, respectively. The shift of short-wavelength edge of 5d–4f emission spectra towards longer wavelengths is observed under temperature increase from 15 to 293K. The observed effects in the spectra of Er3+ and Nd3+ doped crystals were interpreted as a result of reabsorption of 5d–4f luminescence escaping from the bulk of the crystals. [Copyright &y& Elsevier]

Abstract: Luminescence properties of Lu2O3:Eu3+ and Lu2O3:Tb3+ nanocrystalline powders with the particle size varying from 46 to 6nm were studied under excitation by synchrotron radiation in the photon energy range (up to ∼22.5eV) covering the region where the processes of multiplication of electronic excitation occur. It was found that the excitation spectra of Tb3+ emission from all Lu2O3:Tb3+ nanopowders have similar behavior, whereas the shape of the excitation spectra of Eu3+ emission from Lu2O3:Eu3+ nanopowders strongly depends on the particle size. The difference in the behavior of Lu2O3:Eu3+ and Lu2O3:Tb3+ nanophosphor systems was explained by different mechanisms of the energy transfer from the host to Eu3+ or Tb3+ ions (either the hole or electron recombination mechanism, respectively), which are differently influenced by losses of electronic excitations near the particle surface. [Copyright &y& Elsevier]

Abstract: Interconfigurational 4f 105d ↔4f 11 transitions of the Er3+ ion in the YAG host were studied under both VUV photon (synchrotron radiation) and electron beam excitation. It was found that the lowest low-spin 5d level of the Er3+ ion has a rather large energy gap to the next lower 4f 2 D(2)5/2 crystal-field level, which results in a relatively low rate of nonradiative transitions from this 5d level leading to the appearance of weak spin-allowed 5d–4f luminescence at low temperature. The lowest high-spin 5d level, from which spin-forbidden 5d–4f radiative transitions could occur potentially, is situated only at ∼500cm−1 above the 4 D 1/2 level. Such close location allows fast depopulation of the 5d level resulting in the absence of spin-forbidden 5d–4f luminescence and appearance of 4 D 1/2 4f–4f luminescence. [Copyright &y& Elsevier]

Abstract: The low-temperature 4f25d→4f3 fast emission of Nd3+ from YAG:Nd3+ has been studied under excitation by synchrotron radiation. Additionally, 4f3→4f3 luminescence of Nd3+ has been observed and assigned to transitions from the 2F(2)5/2 and 4F3/2 multiplet terms. The observed experimental spectra of Nd3+ d–f emission and f–d excitation are well simulated by crystal-field calculations. [Copyright &y& Elsevier]

• Crystalline K 2 GeF 6 particles were synthesized by co-precipitation. • Fast cross- and intraband luminescence with decay times 300–500 ps was observed. • Transitions between valence sub-bands (Ge 4s,4p, F 2p) cause intraband luminescence. • The decay of K 3p cation excitons results in the formation of Ge 4s,4p holes. • Electronic band structure parameters of K 2 GeF 6 were experimentally determined. Highly crystalline K 2 GeF 6 micropowders were prepared by co-precipitation in the hydrofluoric acid-water-alcohol solution and studied by means of the cathodoluminescence and time-resolved luminescence spectroscopy under synchrotron radiation excitation at 7 K. The nature of various intrinsic emissions was revealed. The luminescence band at 510 nm detected under excitation by photons with the energy above 9 eV is related to the radiative decay of self-trapped excitons. Fast emission bands with ~400 ps decay time found in the spectral range from VUV to visible (8–2.4 eV) are assigned to the cross-luminescence transitions from K 3p hole states and intraband luminescence transitions due to the presence of the Ge 4s, 4p valence states. The creation of cation excitons was detected in the energy range 18–20 eV. Their non-radiative decay results in the formation of hole states in the Ge energy bands, which finally recombine with electrons from the above lying valence states and provide fast intraband luminescence. Important electronic band structure parameters including the energy gap width of 11 eV, cation exciton formation energy 18.1 eV and ionization energy of cation states 20.0 eV were determined from the luminescence excitation spectra. [ABSTRACT FROM AUTHOR]