Evgeny V. Zharikov

Yb-and Er-Doped single crystals of double tungstates NaGd(WO4)2, NaLa(WO4)2, and NaBi(WO4)2 as active media for lasers operating in the 1.0 and 1.5 µm ranges

Ytterbium-and erbium-doped single crystals of scheelite-like double tungstates NaGd(WO4)2, NaLa(WO4)2, and NaBi(WO4)2 and scheelite CaWO4 have been grown by the Czochralski method. The dopant concentrations in crystals are measured, and the coefficients of dopant distribution are determined to range from 0.45 to 3. The lifetimes of the Er3+ states 4I11/2 and 4I13/2 and the Yb3+ state 2F5/2 are measured, and the absorption and luminescence spectra of the crystals are studied in the vicinity of 1.0 and 1.5 µm. The data obtained are compared with the corresponding characteristics of other crystals. The possible use of the crystals studied as active media of solid-state lasers operating in the range 1.0 and 1.5 µm is discussed.

X-ray Diffraction Study of the Structure and Defect System of Yb-Activated (Na0.5Gd0.5)WO4 Crystals

Nominally pure and Yb-activated Czochralski-grown (Na0.5Gd0.5)WO4 crystals (scheelite type) were studied by x-ray diffraction (phase analysis, unit-cell parameters, and structure refinement by the Rietveld method and single-crystal techniques). A pseudotetragonal (orthorhombic) superstructure was revealed, which was shown to have doubled unit-cell parameters compared to the scheelite cell. Some of the crystals were found to contain tungsten and oxygen vacancies, which give rise to additional optical absorption. The effects of the growth and heat-treatment conditions and Yb activation on the structure, defect system, and additional absorption spectrum of (Na0.5Gd0.5)WO4 are analyzed.

High-frequency tunable EPR spectroscopy of Tm3+ ions in synthetic forsterite

The electron paramagnetic resonance spectra of isolated and dimer impurity centers of trivalent chromium ions in the octahedral Ml sites in synthetic forsterite are studied in the frequency range of 65–90 GHz. The measurements are performed at 4.2 K in magnetic field from −0.04 to 0.3 T. The zero-field splitting between spin doublets of the isolated Cr3+ ion Δs= 66.7 GHz and between spin sublevels of the Cr3+-Cr3+ dimer Δd1 = 71.5 GHz and Δd2 = 73.0 GHz is measured directly at zero field. The analysis of the spin Hamiltonian parameters shows that the dimer center consists of a pair of Cr3+ ions with an Mg2+ vacancy between them replacing three Mg2+ ions situated in a quasi-one-dimensional chain aligned parallel to the crystal c-axis. It is found that the exchange interaction in the dimer is ferromagnetic with parameters Jz= 0.47 GHz and Jt = 0.79 GHz.

New laser crystals of complex oxides doped with ions of d elements with variable valence and different structural localization. Review

Ions of d elements in complex oxides with olivine and phenakite structures exhibit diverse structural localization and may incorporate into crystals in various oxidation states. The complexity of the structure of these materials requires a complex approach in investigation of their spectroscopic characteristics with regard to the type of optical center and the growth conditions. The method of estimation of the distribution of an activator ion over crystallographically non-equivalent cationic positions on the basis of the symmetry analysis of the structure of these positions with regard to the spatial distribution of the activator-ion electron density is described. The results of experimental studies of the spectroscopic characteristics of vanadium and chromium ions in the crystals with the olivine (Mg2SiO4, Ca2GeO4, and CaMgSiO4) and phenakite (LiGaSiO4, LiAlGeO4, and Zn2SiO4) structures performed by us (some experimental data are reported for the first time) are analyzed with regard to the growth conditions. Data in the literature are also analyzed. In order to estimate the structural and valence states of the d ions, a number of other experimental techniques were used, and the experimental data were compared with the calculated energy-level diagrams for activator ions in centers of various types. This approach made it possible to adequately describe the possibilities of complex oxides Mg2SiO4, Ca2GeO4, CaMgSiO4, LiGaSiO4, LiAlGeO4, and Zn2SiO4 doped with d ions, regarded as new laser media.

Symmetry of (Na0.5R0.5)MO4 crystals (R = Gd, La; M = W, Mo)

AbstractKinetic order-disorder phase transitions (space group space group

Structural features of phases (Na0.5R0.5)MO4 and (Na0.5R0.5)MO4:R′ (R = Gd, La; R′ = Er, Tm, Yb; M = W, Mo) of the scheelite family

I\bar 4

Molecular self-organization of Ho3+ impurity ions in synthetic forsterite

↔ space group I41/a) have been considered for nonactivated and activated scheelite compounds (Na0.5Gd0.5)WO4 (NGW), (Na0.5Gd0.5)MoO4 (NGM), (Na0.5La0.5)WO4(NLW), and (Na0.5La0.5)MoO4 (NLM) synthesized by the Czochralski method and structural and growth sources of crystal dissymmetrization have been suggested. For NGW, it was shown that an increase in the difference between the content of Gd and Na in two positions of the structure with space group