The luminescent quantum efficiency of Cr3+ ions in Cs2NaAlF6 single crystals

The luminescent quantum efficiency of Cr3+ ions in single fluoride crystal Cs2NaAlF6 was determined by using the simultaneous multiple-wavelength photoacoustic and luminescent experiments method, based on the generation of photoacoustic and luminescence signals after pulsed laser excitation. The luminescent quantum yield for the most important transition between the 4T2→4A2 vibronic levels was found to be 68 ± 3%. This value agrees with that obtained from the ratio of the lifetimes of the corresponding transition at different temperatures.Fil: Torchia, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; ArgentinaFil: Schinca, Daniel Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; ArgentinaFil: Khaidukov, N. M.. Institute of General and Inorganic Chemistry; RusiaFil: Tocho, Jorge Omar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; Argentin

Optical spectroscopy of Yb3+ in the Cs2NaYF6 single crystal

Results of the optical spectroscopy investigation of the cubic paramagnetic center Yb3+ ion in the Cs2NaYF6 single crystal are presented. The Stark level energies of the Yb3+ multiplets are established from absorption, luminescence and excitation luminescence spectra and the crystal field parameters are calculated. Information about the phonon spectra of Cs2NaYF6 crystals is obtained from the electron-vibrational structure of the optical absorption and luminescence spectra. © 2007

EPR and optical spectroscopy of structural phase transition in a Rb 2NaYF6 crystal

The structural phase transition has been observed for the first time in the Rb2NaYF6 crystal and studied by EPR and optical spectroscopy. EPR spectra of Dy3+ and Yb3+ ions present as unintentional dopants in the nominally undoped crystal and forming tetragonal paramagnetic centers have been identified. A characteristic splitting of some optical lines has been observed in the temperature dependence of the Yb3 + optical spectra. It indicates the splitting of the cubic quartet energy levels of Yb3+ ions by the tetragonal crystal field. The empirical schemes of the energy levels for cubic and tetragonal paramagnetic centers of Yb3+ ions have been established and parameters of the corresponding crystal fields have been determined. The latter have been used for analyzing the crystal lattice distortions occurring in the vicinity of the Yb3+ ion during the phase transition. It has been established using the superposition model that the nearest octahedral environment of the Yb3 + ion is distorted as follows: the fluorine ions are rotated by the angle of 2.1 around the fourfold axis; the F- ions located symmetrically in the plane perpendicular to the rotation axis approach the dopant by 0.0014 nm, whereas the F- ions located on the rotation axis move away by 0.0028 nm. It has been concluded that the studied phase transition includes the critical rotations of the octahedral F groups and noncritical displacement of atoms in the rotated fluorine octahedra. © 2013 American Physical Society

ROLE OF THE REGULATORY T CELLS IN PROGRESSION OF PROSTATE CANCER

The existing data on regulatory T cells (Tregs) in prostate cancer suggest that these cells may penetrate the prostate gland malignant tissue, suppressing antitumor immune response, thus promoting aggressive clinical course and low survival of the cancer patients. Evaluation of T cell subpopulations from the tumor microenvironment has shown that the number of CD4+Tregs is associated with inferior clinical prognosis. In particular, each additional CD4+Treg cell has been shown to cause a statistically significant increase in prostate cancer mortality by 12%, regardless of other clinical factors. There are several possible explanations for the increased infiltration of prostate cancer tissue with regulatory T cells. Firstly, malignant cells or tumor-associated macrophages are capable of secreting chemokine CCL22, which has an affinity for the CCR4 receptor expressed on Treg cells. Secondly, cytokines secreted by prostate tumors, such as TGF-β, may regulate the FoxP3 expression, thus expanding the Treg population. TGF-β, in turn, is a multifunctional cytokine that promotes survival and proliferation of transformed cells, including prostate epithelium, as evidenced by increased amounts in the patients with metastatic disease

Spectroscopy and stimulated emission of Nd3+ in an acentric CsY2F7 host

The results of preliminary spectroscopic studies of new fluoride single-crystal CsY2F7 that is activated by Nd3+ ions are given. Direct evidence for the possibility of application of this ordered material as a laser host is given for the first time to our knowledge. Stimulated emission of Nd3+ ions on the main intermultiplet transition is obtained under both nonselective flash-lamp pumping conditions and continuous Ar ion laser pumping conditions. © 1992 Optical Society of America

Evidence for nonmonotonic magnetic field penetration in a type-I superconductor

Polarized neutron reflectometry (PNR) provides evidence that nonlocal electrodynamics governs the magnetic field penetration in an extreme low-k superconductor. The sample is an indium film with a large elastic mean free path (11 mkm) deposited on a silicon oxide wafer. It is shown that PNR can resolve the difference between the reflected neutron spin asymmetries predicted by the local and nonlocal theories of superconductivity. The experimental data support the nonlocal theory, which predicts a nonmonotonic decay of the magnetic field.Comment: 5 pages, 4 figures, LaTex, corrected typos and figure

K2 Y F5 crystal symmetry determined by using rare-earth ions as paramagnetic probes

The electron paramagnetic resonance angular dependences for Gd3+ and Ce3+ centers in K2 Y F5 crystals show that the Y3+ site has monoclinic Ch symmetry in these crystals. This site symmetry is compatible with the crystal structure having the Pnam space group. From the zero-field splitting parameters of the Gd3+ center, it is deduced that the symmetry of the Y3+ sites is close to trigonal around the b axis, distorted by the overall orthorhombic symmetry of the crystal structure. This information is required for the identification of radiation-induced centers in this material, which shows favorable properties for applications as thermoluminescent dosimeter. © 2007 The American Physical Society

Random lattice deformations in rare-earth-doped cubic hexafluoroelpasolites: High-resolution optical spectroscopy and theoretical studies

High-resolution Fourier spectroscopy is used to study the low-temperature (3-10 K) optical absorption spectra of Cs 2NaYF 6 and Cs 2NaScF 6 crystals doped with rare-earth ions, which substitute for Y3 + or Sc3 + ions at sites with cubic O h symmetry. Splitting of some absorption lines corresponding to doublet (Γ 6 or Γ 7)-quadruplet (Γ 8) transitions in the Kramers Yb3 +, Er3 +, and Sm3 + ions and a singlet (Γ 1)- triplet (Γ 4) transition in the non-Kramers Tm3 + ion is observed. In the vicinity of these lines, additional spectral satellites with intensities depending nonlinearly on the concentration of the rare-earth ions are present. We argue that the observed splitting is caused by low-symmetry components of the crystal field induced by random lattice strains. An explicit expression for the generalized distribution function of local strains produced by random point defects in the elastic continuum is derived and used to simulate the line shapes. A satisfactorily agreement with the measured spectra is achieved. The observed satellite transitions are ascribed to pairs of the nearest-neighbor rare-earth ions interacting through the dynamic lattice deformations. © 2012 American Physical Society