B. Macalik

Down- and up-conversion of femtosecond light pulse excitation into visible luminescence in cerium-doped Lu 2 SiO 5 – Gd 2 SiO 5 solid solution crystals co-doped with Sm 3+ or Dy 3+

Luminescence phenomena following femtosecond pulse excitation in UV and IR of Ce(3+) + Sm(3+) and Ce(3+) + Dy(3+) systems in Lu(2)SiO(5) - Gd(2)SiO(5) single crystals are investigated. Effect of excitation wavelength in the UV on Ce(3+) luminescence is interpreted assuming selective excitation of weakly interacting Ce1 and Ce2 sites. IR-excited up-converted spectra differ as compared to UV-excited spectra in that the contribution of Sm(3+) or Dy(3+) luminescence is higher and the Ce(3+) luminescence originates essentially in Ce1 sites. It has been concluded that excitation mechanism of up-conversion involves energy transfer from free electrons created in conduction band of the host.

Precipitation of dopant ions in NaCl:Eu+2 crystals

Abstract The aim of the work presented was to study the effect of the annealing temperature upon the formation of second phases in the NaCl matrix by using the optical absorption and ionic thermocurrent measurements. The 60, 125, 235 and 350°C isotherms were followed mainly for crystals containing 120 mole ppm of divalent europium. The three lower annealing temperatures result in a decay of the impurity-vacancy dipole concentration up to ∼5% of the initial value being accompanied by the growth of metastable phases with their characteristic optical absorption spectra previously observed for as received samples, only. At 350°C the decay of the impurity-vacancy dipole concentration reaches ∼20% of the initial value, and the newly appeared optical absorption spectrum has been ascribed to the stable EuCl 2 precipitates with the PbCl 2 type of structure.

Electric properties of La0.8Sr0.2CoO3 nanoceramics

The electric measurements were carried out for La0.8Sr0.2CoO3 nanoceramics by using impedance spectroscopy methods. The resistance of sample was practically independent of frequency in measurement range. Its dependence on reciprocal temperature showed quite complicated mechanism of conduction. The most striking property of investigated sample was its resistance decreasing with increasing applied polarization.

Effect of codoping LiNbO3:Eu3+ crystal with Mg2+ ions on the Eu3+ optical absorption spectrum

Abstract In this work the optical absorption spectra of Eu3+ doped LiNbO3 measured as a function of Li/Nb ratio are presented. Two Eu3+ sites, dealing with the Nb+5 and Li+ lattice sites, have been characterized by their corresponding 7Fo -5D2 optical transitions. A doubly doped sample (LiNbo3: Mg, Eu) has been used to study the influence of Mg2+ ions on the Eu3+ optical absorption spectrum. The main effect is a shifting of the relative occupation of the two Eu3+ sites.

Thermally stimulated depolarization currents in nickel doped NaCI crystals

Abstract Depolarization currents have been investigated for thermally and mechanically pretreated NaCI crystals doped with divalent nickel ions. The models of Debye and Maxwell-Wagner-Sillars polarizations have been exploited to describe the behavior of ITC bands detected below (dipolar), near and above (interfacial) room temperature, respectively. The NaCI:Ni2+ system was especially interesting for kinetic studies because the dopant ions are distinctly smaller than the matrix cations. It has been found that the precipitation phenomena can be understood in terms of an Avramiapproach of the process mainly occurring in the stress fields of dislocations. The migration of impurities is controlled by the diffusion of cation vacancies.