Search

The results of the investigation of the spectral characteristics of new luminescent substances based on rare-earth ions Eu3 + and Tb3 + in matrices of double molybdates are presented in the article. The luminescence and excitation spectra are considered, the decay times of the main transitions are determined, and the color coordinates are determined. The results show the possible suitability of using these compounds as white phosphor phosphor components., Comment: papers was published in russian

The crystal growth procedure and luminescence properties of pure and Eu$^{2+}$-doped BaBrI and SrBrI crystals are reported. Emission and excitation spectra were recorded under ultraviolet and vacuum ultraviolet excitations. The energy of the first Eu$^{2+}$ 4f-5d transition and SrBrI band gap are obtained. The electronic structure calculations were performed within GW approximation as implemented in the Vienna Ab Initio Simulation Package. The energy between lowest Eu$^{2+}$ 5d state and the bottom of conduction band are found based on luminescence quenching parameters. The vacuum referred binding energy diagram of lanthanide levels was constructed using the chemical shift model.

The work is necessitated by search for new materials to detect ionizing radiation. The rare-earth ions doped with ternary alkali earth-halide systems are promising scintillators showing high efficiency and energy resolution. Some aspects of crystal growth and data on the structural and luminescence properties of BaBrI and BaClI doped with low concentrations of $\mathrm{Eu^{2+}}$ ions are reported. The crystals are grown by the vertical Bridgman method in sealed quartz ampoule. New crystallography data for BaClI single crystal obtained by single crystal X-ray diffraction method are presented in this paper. Emission, excitation and optical absorption spectra as well as luminescence decay kinetics are studied under excitation by X-ray, vacuum ultraviolet and ultraviolet radiation. The energies of the first 4f-5d transition in $\mathrm{Eu^{2+}}$ and band gap of the crystals have been obtained. We have calculated the electronic band structure of the crystals using density functional theory as implemented in the \latin{Ab Initio}. Calculated band gap energies are in accord with the experimental estimates. The energy of gaps between the occupied Eu$^{2+}$ 4f level and the valence band top are predicted. In addition, positions of lanthanide energy levels in relation to valence band have been constructed using the chemical shift model., Comment: 28 pages, 10 figures

Optical spectra (absorption, emission, excitation, decay) and dielectric relaxation were measured for divalent europium (and partially for ytterbium) in lanthanum fluoride crystals. Absorption of Eu$^{2+}$ contains not only asymmetric weakly structured band at 245 nm but also long-wavelength bands at 330, 380 nm. Broadband Eu$^{2+}$ emission at 600 nm appeared below 80 K, having decay time 2.2 $\mu$s at 7.5 K. Emission at 600 nm is attributed to so-called anomalous luminescence. Bulk conductivity is directly proportional to absorption coefficient of Eu$^{2+}$ bands. Dielectric relaxation peak of LaF$_3$-EuF$_3$ is attributed to rotation of dipoles Eu$^{2+}$-anion vacancy. The long-wavelength absorption bands at 330, 380 nm are assigned to transitions from 4f$^7$ Eu$^{2+}$ ground state to states of neighbouring fluorine vacancy., Comment: presented on LUMDETR2015 conference, submitted to Radiation Measurements

It was shown that the divalent rare earth ions (La, Ce, Gd, Tb, Lu, and Y) in cubic sites in alkaline earth fluorides are unstable with respect to electron autodetachment since its d1(eg) ground state is located in the conduction band which is consistent with the general tendency of these ions in various compounds. The localization of doubly degenerate d1(eg) level in the conduction band creates a configuration instability around the divalent rare earth ion that leading to the formation of anion vacancy in the nearest neighborhood, as was reported in the previous paper [Journal of Physics and Chemistry of Solids 74 (2013) 530-534]. Thus, the formation of the stable divalent ions as La, Ce, Gd, Tb, Lu, and Y (PC+ centers) in CaF2 and SrF2 crystals during x-ray irradiation occurs via the formation of charged anion vacancies near divalent ions (Re2+va), which lower the ground state of the divalent ion relative to the conductivity band. Photochromic effect occurs under thermally or optically stimulated electron transition from the divalent rare earth ion to the neighboring anion vacancy and reverse under ultraviolet light irradiation., Comment: 22 pages, 9 figures

We have studied the absorption spectra of x-ray irradiation-induced Ce2+ and Pr2+ ions in crystals of alkaline-earth fluorides. We have calculated absorption spectra of divalent praseodymium ions in SrF2 crystals doped with Pr2+ for the first time. The calculated spectra agree rather well with the experimental data. In crystals containing induced Ce2+ ions we have found strong electron-phonon coupling. In BaF2, we do not observe bands corresponded to divalent Ce or Pr ions., Comment: 14 pages, 5 figures, 1 table

In this paper results of scintillation properties measurements of pure and Ce3+-doped strontium fluoride crystals are presented. We measure light output, scintillation decay time profile and temperature stability of light output. X-ray excited luminescence outputs corrected for spectral response of monochromator and photomultiplier for pure SrF2 and SrF2-0.3 mol.% Ce3+ are approximately 95% and 115% of NaI-Tl emission output, respectively. A photopeak with a 10% full width at half maximum is observed at approximately 84% the light output of a NaI-Tl crystal after correction for spectral response of photomultiplier, when sample 10x10 mm of pure SrF2 crystal is excited with 662 KeV photons. Corrected light output of SrF2-0.3 mol.% Ce3+ under 662 KeV photon excitation is found at approximately 64% the light output of the NaI-Tl crystal., Comment: 4 pages, 4 figures and 1 table