A detailed spectroscopic study of ${\text{Yb}}^{3+}:{\text{CaF}}_{2}$ is made by using laser selective excitation, low-temperature time-resolved fluorescence, and Raman techniques. Three dominant types of ${\text{Yb}}^{3+}$ isolated ion centers are identified at very low $(0.03\text{ }\text{at}\text{.}\text{ }%)$ dopant concentration: two of them with cubic and tetragonal symmetries and the third one not clearly identified but likely of trigonal symmetry. Fluorescence decays strongly differ from one site to another. The overall measured positions of the Stark sublevels of the ${^{2}F}_{7/2}$ and ${^{2}F}_{5/2}$ multiplets are satisfactorily explained by the crystal-field calculations. On the other hand, at higher dopant concentrations, only one dominant class of ${\text{Yb}}^{3+}$ centers occurs which corresponds to some hexameric cluster in which the ${\text{Yb}}^{3+}$ ions site in nearly tetragonal crystal-field environments and whose energy-level positions are discussed and compared with those previously reported in the literature.

Spectroscopy of Yb 3+ :CaF 2 : From isolated centers to clusters

In this paper, the question posed in the title is critically examined on the basis of the available literature evidence implying the positive answer. The distinction between, on the one hand, the actual crystal field (CF) or equivalently ligand field (LF) related quantities and, on the other hand, the actual zero-field splitting (ZFS) or equivalently fine structure (FS) quantities, is elucidated. The origin and possible roots of the incorrect terminology consisting in mixing up the two physically distinct quantities at different levels are examined. Aspects concerning Hamiltonians, parameters, energy level splitting, and nature of the operators involved are taken into account. Problems with the various notations for the operators and parameters used in the electron magnetic resonance (EMR) area are also identified and reviewed. A large number of cases of incorrect terminology and other inconsistencies identified in the course of a comprehensive literature survey are analyzed and systematically classified. Implications of the confusion in question, which go beyond the simple semantic issues, are discussed. The results of the survey reveal that the two most serious categories of this confusion lead to misinterpretation of the experimental EMR data. Several examples of serious misinterpretations found in the books, reviews, and original papers are discussed. The incorrect terminology contributes also to misleading keyword classifications of papers in journals as well as references in scientific literature databases. Thus, the database searches may produce unreliable outcomes. Examples of such outcomes are also shown. It is concluded that, in order to prevent further proliferation of the incorrect terminology and thus to increase reliability of the published EMR data, a concerted effort within the EMR community is indispensable. Various ways in this regard at the international level are suggested.

Can the electron magnetic resonance (EMR) techniques measure the crystal (ligand) field parameters

Effect of L-threonine (LT) doping on crystalline perfection, second harmonic generation (SHG) efficiency, optical transparency, and laser damage threshold (LDT) in potassium dihydrogen phosphate (KDP) crystals grown by slow evaporation solution technique (SEST) has been investigated. The influence of doping on growth rate and morphology of the grown crystals has also been studied. Powder x-ray diffraction data confirms the crystal structure of KDP and shows a systematic variation in intensity of diffraction peaks in correlation with morphology due to varying LT concentration. No extra phase formation was observed which is further confirmed by Fourier transform Raman (FT-Raman) studies. High-resolution x-ray diffraction curves indicate that crystalline perfection has been improved to a great extent at low concentrations with a maximum perfection at 1 mol % doping. At higher concentrations (5 to 10 mol %), it is slightly reduced due to excess incorporation of dopants at the interstitial sites of the crystalline matrix. LDT has been increased considerably with increase in doping concentration, whereas SHG efficiency was found to be maximum at 1 mol % in correlation with crystalline. The optical transparency for doped crystals has been increased as compared to that of pure KDP with a maximum value at 1 mol % doping.

/pdf/remarkable-enhancement-in-crystalline-perfection-second-221mdv4kw4.pdf

Remarkable enhancement in crystalline perfection, second harmonic generation efficiency, optical transparency, and laser damage threshold in potassium dihydrogen phosphate crystals by L-threonine doping

EPR detection of the flux distribution in ceramic high-Tc superconductors

One- and two-photon spectroscopy of f → d and f → f transitions of Eu2+ ions in M1-xNxF2 mixed fluoride crystals (M, N = Ba, Sr, Ca; 0 ⩽ x ⩽ 1)

We report here experimental data on the crystal-field interaction of gadolinium ions with their environment in ${\mathrm{Gd}}_{x}{\mathrm{Eu}}_{1\ensuremath{-}x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$. The ESR spectrum and a Schottky anomaly in the specific heat of dilute samples ($x\ensuremath{\ll}1$) indicate the existence of a crystal-field splitting of the $^{8}S_{\frac{7}{2}}$ ground state of ${\mathrm{Gd}}^{3+}$ ions of about 1.5 K. We discuss the parametrization of the measured splitting in terms of an effective Hamiltonian, and the microscopic origin of the interaction within the framework of a superposition model. Since the single-ion energies involved are of the same order of magnitude as the energies associated with the magnetic ordering of the ${\mathrm{Gd}}^{3+}$ moments in $\mathrm{Gd}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ (${T}_{N}\ensuremath{\cong}2.24$ K), we analyze the effects of the crystal-field interaction on the magnetic transition.

/pdf/crystal-field-interaction-in-the-gdxeu1-xba2cu3or7-delta-4401ddlhhj.pdf

Crystal-field interaction in the GdxEu1-xBa2Cu3OR7- delta superconductors.

We have calculated the lattice distortions around trivalent rare-earth dilute impurities, occupying substitutionally metal sites in fluorites. Explicit results are given for the equilibrium positions of the nearest fluorine ligands, $R$, the induced electric dipole moments, and the local hydrostatic strains for $M{\mathrm{F}}_{2}$ ($M=\mathrm{C}\mathrm{d},\phantom{\rule{0ex}{0ex}}\mathrm{C}\mathrm{a},\phantom{\rule{0ex}{0ex}}\mathrm{S}\mathrm{r},\phantom{\rule{0ex}{0ex}}\mathrm{P}\mathrm{b},\phantom{\rule{0ex}{0ex}}\mathrm{a}\mathrm{n}\mathrm{d}\phantom{\rule{0ex}{0ex}}\mathrm{B}\mathrm{a}$). These results are used to study the impurity-ligand distance dependence of the fourth-order cubic-crystal-field parameter, ${b}_{4}$, for ${\mathrm{Gd}}^{3+}$ and the isoelectronic ion ${\mathrm{Eu}}^{2+}$. Comparison is made with the change of ${b}_{4}$ with hydrostatic stress using the calculated local compressibility of the lattice. A consistent description of the experimental data is obtained assuming ${b}_{4}\ensuremath{\propto}{R}^{\ensuremath{-}m}$ with $m\ensuremath{\sim}10$.

Lattice distortions and local compressibility around trivalent rare-earth impurities in fluorites

A comparative study by means of resonant Raman scattering and optical transmission spectroscopy between the different color centers originating from Fe~III! and Cu~II! doping of L-alanine crystals is presented. In both samples we find a selective resonant enhancement of Raman active modes related to vibrations of the lattice and carboxyl group. We found that Cu~II!- and Fe~III!-doped samples have qualitatively similar electronic absorptions, but they display different effects on the resonant profiles of the phonons. Fe~III!-doped samples show an antiresonance behavior for some modes, something that is not observed in samples with Cu~II! impurities.

Resonant Raman scattering and optical transmission studies of Cu(II) and Fe(III) impurities in crystalline L -alanine

The color centers in electron irradiated L-alanine crystals are studied by means of resonant Raman scattering and photoluminescence. We find a selective resonant enhancement of some of the Raman-active vibrations. The Raman resonant modes are either localized at the methyl group or belong to lattice modes comprising displacements of the ammonium group in the damaged amino acid molecules. The luminescence intensity wanes with increasing temperature above an onset of ;150 K, indicating a strong interaction of the photoexcited electrons in the defects with the lattice modes. These results are compared with the electronparamagnetic-resonance absorption brought forth by these defects. A simple model calculation that explains the experimental results qualitatively is presented. It is shown that optical spectroscopy provides a valuable technique to study color centers in organic crystals on account of the spatial information of the wave function that can be obtained by resonant Raman scattering. @S0163-1829~98!03221-4#

C. Fainstein

Papers

Crystal-field interaction in the GdxEu1-xBa2Cu3OR7- delta superconductors.

Lattice distortions and local compressibility around trivalent rare-earth impurities in fluorites

Resonant Raman scattering and optical transmission studies of Cu(II) and Fe(III) impurities in crystalline L -alanine

Luminescence and resonant Raman scattering of color centers in irradiated crystalline L-alanine

Ligand electron-nuclear double resonance of 19F ions around Yb3+ impurities in fluorites.