Intensity and bandwidth of multiphonon vibronic transitions of rare-earth ions in crystals

The theory of multiphonon vibronic coupling to electronic transitions is applied in analysing fluorescence spectra of Eu²⁺ in BaFCI, which consist of the 4f⁷(⁶P_7/2,) → 4f⁷(⁸S_7/2) and 4f⁶5d → 4f⁷ transitions, and the 4f⁷-4f⁶5d excitation spectrum of Ce³⁺ in YPO⁴. The 4f electrons are weakly coupled to lattice vibration modes so that only weak one- and two-phonon sidebands are observable in the 4f-4f optical transitions, whereas the electron-phonon coupling is significantly stronger for a 5d electron. Accordingly, intensive multiphonon vibronic transitions overwhelmingly dominate the 4f⁶5d → 4f⁷ spectrum. It is shown that the extended Judd-Ofelt theory for weak vibronic coupling in the framework of the M-process is equivalent to the Huang-Rhys theory for the δ-process. In the analysis of experimental data, contributions from local ligand modes and lattice acoustic modes are separated, and the coupling strength is evaluated, in terms of the Huang-Rhys parameter S, for the 4f-4f and 5d-4f vibronic transitions.     

Influence of excited configurations on the intensities of electric-dipole transitions of rare-earth ions

The theory of induced electric-dipole transitions of rare-earth ions in crystals and glasses is improved by taking into account the third-order effects of perturbation theory with respect to the energies of virtual excitations of 4f electrons to the 5d states. Since the energy regions of excited 4f ^{N ? 1}5d states are usually superimposed with the charge-transfer bands, the effects caused by a virtual transfer of an electron from the outer shells of ions of the surroundings (ligands) to the unfilled 4f ^N shells are also considered. The Pr³⁺, Sm³⁺, and Eu³⁺ ions are considered as examples. It is found that some difficulties inherent in the Judd-Ofelt calculation scheme are successfully overcome. The agreement of the calculated results with the experimental data improves.     

On the crystalline field of rare-earth ions in the cubic intermetallic compound: YSb

Resolved fine structure spliting of Gd in YSb yields a fourth order crystalline field parameter b₄ = (29±3)G. A correlation between b₄ and the crystalline field experienced by other rare-earth ions in the same host is demonstrated.     

Crystal field parameters and shifts of the Slater integrals for rare-earth ions in metals

The Fermi-Thomas model screening of a charge in metals is used to derive the crystal field parameters and to predict the shifts of the Slater parameters of rare-earth ions in metals. Numerical estimates are given for PrSb.     

Behavior of high-spin molecules and rare-earth ions in a bifrequency AC magnetic field

The behavior of high-spin molecules and rare-earth ions subject to a bifrequency AC magnetic field has been studied theoretically for times much greater than the relaxation times which characterize transitions between three lowest levels of a molecule (a stationary process). The bifrequency AC field is a superposition of intense and weak AC fields with different frequencies and polarizations. The nonlinear susceptibility of the molecules has been found. It has been shown that the intense AC field influences the absorption of the weak AC field. A way of estimation of some phase relaxation times of the molecule is suggested.     

Magnetooptics of magnetic-dipole transitions in the rare-earth paramagnetic garnets

The Faraday effect (FE) of the rare-earth (RE) paramagnetic garnet crystals associated with magnetic-dipole (MD) transitions has been investigated theoretically over a wide temperature range 80 to 300 K. Over this temperature range, the ??gyromagnetic?? Verdet V _gm ^(m) of the Eu₃Ga₅O₁₂ (EuGG) is not a linear function of the magnetic susceptibility ?? measured along the [111] axis. We find that the nontrivial character of the temperature dependence of the MD Verdet constant V _gm ^(m) is associated with the presence of a contribution to the Faraday rotation of the Van Vleck ??mixing?? by an external magnetic field of the Eu³⁺ electronic states. The optical absorption and magnetic circular dichroism (MCD) of Eu³⁺ ion in EuGG at 85 K for the MD transition ⁷ F ₀ ?? ⁵ D ₁ were measured along the [111] axis. We show that the appearance of the MCD feature observed for the absorption line near 526.6 nm for the ⁷ F ₀ ?? ⁵ D ₁ MD absorption band may be well-explained by the contribution of Van Vleck ??mixing?? between the Stark singlet states from the ⁷ F ₀ and ⁷ F ₁ multiplet manifolds mixed by the external magnetic field H.     

Two-particle configuration interaction in rare-earth ions

Summary The two-particle configuration interaction by way of Coulomb field in rare-earth ions is considered and the interaction energy matrices for the commonly studied cases off ⁿ (n=2, 3, 4) are calculated in terms of three parameters.     

Mechanism of dissipation of the excitation energy in garnet oxides doped with rare-earth ions with 4f-5d transitions

Mechanisms of dissipation of the excitation energy in garnet crystal phosphors Y₃Al₅O₁₂ and Y₃Ga₅O₁₂ doped with rare-earth ions with interconfiguration transitions are studied depending on the Ga concentration.     

Hypersensitive transitions of Tm3+, Ho3+ and Dy3+ rare-earth ions in garnet crystals

In this work, spectroscopic characteristics (oscillator strengths, intensity parameters) of intermanifold f–f transitions of Tm^{3 +}, Ho³⁺and Dy³⁺ions in garnet crystals are investigated. It has been found that the intensity change of the hypersensitive intermanifold f–f transitions of rare-earth ions in garnet crystals is determined by the characteristics of their local environment.     

Magnetic field stimulated transitions of excited states in fast μHe+ ions

It is shown that one can stimulate, by using the present-day laboratory magnetic fields, transitions between the lm sub-levels of fast μHe⁺ ions formed in muon catalyzed fusion. This gives a possibility to drive the population of the lm sub-levels by applying a field of a few Tesla, which affects the reactivation rate and is especially important to the Kα X-ray production. Strong fields also cause the self-ionization from highly excited states of the muonic helium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Intensities of hypersensitive transitions in garnet crystals doped with Er<Superscript>3+</Superscript> ions

We examine the oscillator strengths and the intensity parameters Ω _t (t = 2, 4, 6) of yttrium-aluminum, scandium-containing, and gallium garnet crystals doped with Er³⁺ ions. A comparative analysis of the oscillator strengths and the intensity parameters Ω _t (t = 2, 4, 6) of garnets with different contents of Al³⁺ and Sc³⁺ ions (Gd_2.4Er_0.5Sc_1.8Al_3.3O₁₂, Gd_2.4Er_0.5Sc_1.9Al_3.2O₁₂, Gd_2.4Er_0.5Sc_2.0Al_3.1O₁₂) is performed, as a result of which the oscillator strengths and the intensity parameters Ω _t (t = 2, 4, 6) of these crystals are shown to have close values. We find that Ca₃(NbGa)₅O₁₂ crystals doped with Er³⁺ ions are characterized by highest values of the oscillator strengths for hypersensitive transitions and of the intensity parameter Ω₂ of Er³⁺ ions compared to the values of these quantities in the examined garnet crystals, which is determined by the fact that the symmetry of the local environment of Er³⁺ ions in these crystals is C ₁, C ₂, or C _2ν. We reveal that, as the concentration of Er³⁺ ions in these crystals increases from 1 to 39 at %, both the oscillator strength of the hypersensitive transition ⁴ I _15/2 → ² H _11/2 of Er³⁺ ions and their intensity parameter Ω₂ tend to decrease, which can be related to an increase in the relative fraction of Er³⁺ ions with higher symmetry of the local environment.