Calculating the energy spectra of magnetic molecules: application of real- and spin-space symmetries

The determination of the energy spectra of small spin systems as for instance given by magnetic molecules is a demanding numerical problem. In this work we review numerical approaches to diagonalize the Heisenberg Hamiltonian that employ symmetries; in particular we focus on the spin-rotational symmetry SU(2) in combination with point-group symmetries. With these methods one is able to block-diagonalize the Hamiltonian and thus to treat spin systems of unprecedented size. In addition it provides a spectroscopic labeling by irreducible representations that is helpful when interpreting transitions induced by Electron Paramagnetic Resonance (EPR), Nuclear Magnetic Resonance (NMR) or Inelastic Neutron Scattering (INS). It is our aim to provide the reader with detailed knowledge on how to set up such a diagonalization scheme.Comment: 29 pages, many figure

Optical lines in europium-terbium double activated calcium tungstate phosphor

The Letter is devoted to the problem of the optical anisotropy of the rare-earth ions occupying low-symmetry positions in crystals. The crystal field multiplets arising from LSJ terms of Eu3+ and Tb3+ ions in the crystal field of calcium tungstate scheelite (CaWO4) are analyzed with regard to the experimental data on the low temperature photoluminescence and cathodo-luminescence spectra. The selection rules as well as an angular (polarization) dependence of the two-photon absorption are discussed. (C) 2004 Elsevier B.V. All rights reserved.This research was supported by the International Cooperation Research Program of the Ministry of Science and Technology, Republic of Korea. Financial support USA–Israel Binational Science Foundational (Proposal No. 2002409) is highly appreciated

Luminescence properties of europium-terbium double activated calcium tungstate phosphor

Double incorporation of Eu3+ and Tb3+ ions into a CaWO4 crystalline lattice modifies the luminescence spectrum due to the formation of new emission centers. Depending on the activators concentration and nature, as well as on the interaction between the activators: themselves, the luminescence color can be varied within the entire range of the visible spectrum. Variable luminescence was obtained when CaWO4:Eu,Tb phosphors with 0-5 mol% activator ions were exposed to relatively low excitation energies as UV (365 and 254 nm). Under high energy excitation such as VUV (147 nm) radiation or electron beam, white light has been observed. This material with controlled properties seems to be promising for the applications in fluorescent lamps, colored lightning for advertisement industries, and other optoelectronic devices. (C) 2004 Elsevier Ltd. All rights reserved.This research was supported by a grant (M1-02-KR-01- 0001-02-K18-01-025-1-3) from Information Display R&D Center, one of the 21st Century Frontier R&D Program funded by the Ministry of Science and Technology of Korean government