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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]

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. [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]

Zirconium dioxide films grown by atomic layer deposition from ZrCl[SUB4] and H[SUB2]O at substrate temperatures of 500-870 K were characterized using spectroscopic methods. A significant influence of the phase composition on absorption and photoluminescence spectra was observed. The band-gap energies determined from absorption spectra of films with monoclinic structure grown at 670-870 K ranged from 5.25 to 5.28 eV. Low-temperature (10 K) photoexcitation of these films resulted in a non-elementary emission band with the maximum at 4.25-4.35 eV, tentatively assigned to the radiative decay of self-trapped excitons. The low-energy edges of the excitation spectra coincided with the edges of intrinsic absorption. A film that was grown at 500 K and contained tetragonal ZrO[SUB2] with large amounts of impurities had an absorption edge at 5.26 eV and wide emission band at 3.0 eV, which could be excited at as low photon energy as 4.9 eV. [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]

Abstract: Emission spectra at 10K employing synchrotron radiation have been recorded for the tripositive lanthanide ions, Ln=Sm, Gd, Tb, Ho, and Er situated at octahedral (or nearly octahedral) site symmetry in hexafluoroelpasolite Cs2NaMF6 (M=Y, Sc, or Ga) lattices. Interconfigurational 5d→4f transitions are only observed for Er3+, and the intensity ratio of 4f105d→4f11 emission, compared with 4f11 →4f11 emission, with excitation into 5d levels, is greater for M=Ga than M=Sc. The highest energy intraconfigurational emission is from 4G5/2 (Sm3+), 6P7/2 (Gd3+), 5D3 (Tb3+), 5G4 (Ho3+), and 2F(2)7/2 (Er3+). Detailed energy level assignments have been given for Ln=Sm, Gd, and the remaining spectra are assigned as multiplet–multiplet transitions. [Copyright &y& Elsevier]