Miroslaw Zaleski

Magnetic Ordering of Dy3+ Ions in RbDy(WO4)2 Single Crystal

The specific heat C(T) of the monoclinic RbDy(WO4)2crystal has been studied at very low temperatures 0.2≤T≤1.9 K and in magnetic fields 0≤H≤0.38 T. The Neel temperature was shown to be equal to TN = 0.818 ± 0.005 K. The experimental value of the effective exchange parameter was obtained to be equal to J/k = − 0.798 K. The C T) dependence below Neel temperature 0.5TN<T<0.99TN) is well described by 2D Ising model, whereas in the temperature region close above TN(1.01 TN<T< 2TN) it can be described by neither 2D, nor 3D Ising model. The experimental and theoretical H-TNdiagrams for fieldH ‖ aare in a reasonable agreement for simple quadratic lattice.

Structural Phase Transition in K1‐xCsxDy(WO4)2 Single Crystals

Single crystals of dysprosium potassium (caesium) double tungstates were grown both by typical flux growth and Top Seeded Solution Growth. K 2 W 2 O 7 was used as flux. Potassium tungstate provides broad range of growth temperatures, rather low volatility, and does not introduce additional components into the melt. K 1-x Cs x Dy(WO 4 ) 2 crystals belong to the monoclinic syngony (α-KY(WO 4 ) 2 structure) and has the space group C2/c. Dy ions are situated on the two-fold axes (C 2 ) (which coincide with the crystallographic [010] directions) inside distorted octahedra of oxygen ions. KDy(WO 4 ) 2 is known to undergo a structural phase transition of Jahn-Teller type at 6.38K. The influence of caesium ions on structural phase transition was investigated. Spectroscopic studies of this compound at low temperature have revealed some peculiarities of optical absorption spectra. The ground state of the Dy 3+ ions is split into Kramers doublets with the first excited doublet lying closely to the ground doublet what determines the thermal behaviour of absorption spectra. The increase of the distance between the Dy 3+ lowest doublets observed at low temperature is interpreted as the result of the cooperative Jahn-Teller effect.

Magnetic structure of ground state of the KDy(WO4)2 single crystal

Abstract The data of low-temperature magnetic measurements of the monoclinic KDy(WO 4 ) 2 crystal are used to calculate the exchange and dipole–dipole interactions energy. The last are used for the determination of the magnetic structure of the ground state.

Optical properties of ADy(WO4)2single crystals (A=K,Rb,Cs)

The investigations of the optical absorption spectra of the ADy(WO4)2 (where A equals K, Rb,) single crystals have shown that the phase transitions found at 6.38 K for KDy(WO4)2, 4.9 K, 9.0 K for RbDy(WO4)2, exhibit the peculiarities characteristic of structural phase transition of Jahn-Teller type. The paper presents also the results of VIS absorption investigations of the K(1-x))CsxDy(WO4)2 mixed single crystals.

Rapid thermal bleaching in doped sillenites

Thermal stability of photochromic effect existing at temperatures below 100 K in scandium doped germanium sillenites (BGO:Sc) was investigated. The single crystals of sillenites were obtained by the Czochralski technique. Some thermally stimulated processes related to the photochromic properties of doped sillenites were noticed. Process of thermal bleaching was studied in a wide spectral range and in various conditions. Both equilibrium thermal bleaching and non-equilibrium one leading to so called thermoabsorption were intensively studied. On the base of proposed model of thermoabsorption the energies of trap centers were calculated. It has been shown that some optical properties of sillenites are very sensitive to the procedure and conditions in which the coloring process was provided.

Photochromism of mixed sillenites

Optical properties of some mixed B12TiO20 (BiTiO) and Bi40Ga2O63 (BiGaO) single crystals were investigated. The mixed single crystals have been grown with use of Top Seeded Solution Growth technique and Ti ion was substituted with V, Pb or Ga ions. Thermal conditions enabling growth of uniform [110] BiTiO and BiGaO single crystals with totally flat (110) interface have been found. Special interest was devoted to the problem of photochromic effect existing in investigated single crystals at temperatures lower than 200 K. The characteristic temperature of thermal bleaching and the wave length active in a coloring process (the coloring spectra) for all mixed single crystals were established. It was noticed that the substitution of some ions in tetrahedral positions had essential effect on photochromic properties of investigated mixed sillenites. In this case the photochromic effect should be related to the fundamental edge shift.

Pleochroism (trichroism) of dysprosium-alkali metal double tungstates

The main absorption spectra and the main refractive indices of the ADy(WO4)2 (where A equals K, Rb,) single crystals have been investigated. The existence of three different spectra (trichroism) along the three optical axes of the crystals have been revealed. Using optical microscopy method main refractive indices have been found.

Influence of scandium doping on temperature dependences of photochromic absorption of sillenites

Single crystals of scandium doped germanium sillenite (BGO:Sc) were obtained by the Czochralski method. The absorption and photochromic spectra were investigated as a function of temperature. For comparison the same spectra for nominally pure crystals were measured too. Scandium doping influences significantly on spectral dependences only at about 8000 cm-1. But the presence of Sc ions modifies strongly the temperature dependences of spectra. The characteristic photochromic temperature T0 for BGO:Sc is determined to be about 100 K. This value is higher than T0 for pure material. The main part of the photochromic spectrum is divided into 4 absorption bands (at 8350, 11660, 18090, 21350 cm-1). The fifth band is in the UV and it was not investigated in this paper. On the base of different temperature dependences the above four absorption bands are attributed to two centers.

Photochromic effect in Bi12GeO20:Ce

For the first time the photochromic effect for cerium doped bismuth-germanium oxide Bi12GeO20 is presented. The results for coloring and optical decoloring at room temperature and at liquid nitrogen temperature are shown as function of illuminating light. The coloring of BGO:Ce crystals produces two different photochromic states dependent on the coloring temperature.

Raman and IR spectroscopy investigations of double tungstates

The investigations of the Raman scattering spectra of the KDy(WO4)2 single crystals have shown that the phase transitions found at 6.38 K exhibit the peculiarities characteristic of SPT Jahn-Teller type. The paper presents also the results of IR absorption investigations of the ADy(WO4)2 single crystals, where A equals K, Rb.