Zero magnetic field splitting and anomalies of intensities in the Zeeman spectra of La(Pr)Cl3-crystals

Optical absorption and Zeeman effect measurements on La(Pr)Cl₃ show a zero magnetic field splitting of the degenerate Pr³⁺ levels and . The site symmetry of the Pr³⁺ ions is lowered fromC _3h toC _s . The resultant splittings of the doublet levels are:I ³ H ₄:2|T _ak |=(0.12±0.05)cm^–1;a ³ P ₁:2|T _al |=(0.10±0.05)cm^–1.The intensities of the optical transitions induced by the deformation decrease with increasing magnetic field. All observations are described by a first order perturbation calculation using a low symmetric part of the crystal field and Zeeman energy as simultaneous perturbations on a Pr³⁺ ion in a crystal field with site symmetryC _3h .Project of the Sonderforschungsbereich Festkörperspektroskopie SFB65, Darmstadt—Frankfurt, supported by the Deutsche Forschungsgemeinschaft.     

Room temperature emission from the Pr3+ 1 S 0-level in PrF3

PrF₃ as well as PrF₃-LiF and PrF₃-MgF₂ mixtures were investigated by means of high-energetic excitation with synchrotron radiation. In the PrF₃ emission spectrum bands due to the intra-configurational 4f²4f² transitions originating from the ¹S₀ level of the Pr³⁺ ion have been identified. The emission from the ³P₀ multiplet is very weak due to non-radiative decay by cross-relaxation processes. Therefore, PrF₃ is not an efficient direct cascade emitter. In the PrF₃ excitation spectra in the ultraviolet/vacuum-ultraviolet spectral range, the ³H₄¹S₀ transition at 46858 cm^-1 as well as broad bands due to the inter-configurational 4f²4f5d transitions are observed. By comparison with data of Pr³⁺ doped YF₃, the branching ratios of the emission transitions for PrF₃ from the ¹S₀ were determined; these are 0.008, 0.075, 0.262, 0.023 and 0.629 for transitions ¹S₀³H₄, ³F₄, ¹G₄, ¹D₂ and ¹I₆, respectively. For the polycrystalline PrF₃-LiF and PrF₃-MgF₂ samples investigated by us, the measured emission and excitation spectra are nearly identical to those of PrF₃. For polycrystalline PrF₃-KMgF₃ the observed spectra are superpositions of the PrF₃ and Pr³⁺:KMgF₃ spectra. PACS 42.70.-a; 78.55.-m; 78.55.Hx     

晶场二级效应与交换作用对PrF3晶体磁性及磁光性质的影响

研究了晶场二级效应在PrF₃晶体中的作用，发现该效应可使Pr³⁺离子的晶场单态与其他态混合，对PrF₃晶体磁化率产生明显影响.进一步研究了晶体内的交换作用有效场，其形式为H_in=(1.9-0.02556T)×10^-5M，在100—300 K的温度范围内，以此计算的PrF₃晶体的倒数磁化率和Verdet常数的倒数与实验值符合较好.结果表明，在PrF₃晶体中，晶场二级效应与离子间的交换作用都不能忽略. 关键词： 晶场二级效应 交换作用有效场 Verdet常数 3晶体')" href="#">PrF₃晶体     

Ce and Pr5d-energy levels in the (pseudo) perovskites KMgF3 and NaMgF3

The location of the 5d-energy levels of Ce³⁺ and Pr³⁺ in the cubic perovskite KMgF₃ and in the distorted perovskite NaMgF₃ was determined from spectroscopic studies in the vacuum ultraviolet. It is established that Ce³⁺ and Pr³⁺ ions both occupy the same site in each host: K⁺ sites for KMgF₃ and Na⁺ sites for NaMgF₃. The small crystal field splitting and the small value of the centroid shift of the 4fⁿ⁻¹5d-configuration yield a relatively high energy for the lowest 5d state of both Ce³⁺ and Pr³⁺. The lowest 5d state of Pr³⁺ in both hosts is found at energy higher than the 4f² state, enabling the photon cascade emission to occur.     

Calculation of the energy-level scheme of Pr3+ in crystalline PrF3 from optical and inelastic neutron scattering data

By using a semi-empirical fitting approach and appropriate results of optical spectroscopy and inelastic neutron scattering experiments the energy-level scheme of the crystal field-splitted ³H₄-multiplet of Pr³⁺ in PrF₃ is determined. The results are shown to be in good agreement with the experiments.     

Praseodymium luminescence in fluorides

This work is a continuation of studies of the Pr³⁺ cascade emission in various matrices. The effect of the environment of the luminescence center on the mutual position of the lowest 5d and the 4f level ¹S₀ of Pr³⁺ is considered. PrF₃ clustering in BaF₂ is observed at a high praseodymium concentration. The promising potential of magnesium as a charge compensator for praseodymium in SrAlF₅ is demonstrated.     

The effect of the crystal-field ground-state splitting on the electrical resistivity of dilute (La,Pr)B6

We have measured the resistivity and the magnetoresistivity of some dilute (La, Pr)B₆ single crystals. At temperatures below 1 K a pronounced step in the resistivity occurs which shifts to higher temperatures with increasing Pr concentration as well as with increasing external magnetic fields. The observed resistance anomaly is caused by Pr–Pr interactions which remove the degeneracy of the ₅ crystal field ground state of Pr³⁺ in LaB₆. The resistance step reflects the temperature-dependent probability that conduction electrons are scattered from the ₅ crystal field sublevels of the Pr³⁺ ions. The shift of the resistance step in a magnetic field can be simply explained as Zeeman effect of the ₅ triplet.     

Infrared study in high magnetic fields of the crystal-field excitations in PrMnO3

Pr³⁺ ion crystal field (CF) excitations in PrMnO₃ single crystals have been studied by infrared transmission, in the 1800–8000 cm⁻¹ range, as a function of temperature and applied magnetic field up to 13 T. No noticeable frequency shifts which might occur below T_N∼100 K, as a result of the antiferromagnetic transition, are observed in the Pr³⁺ CF levels. A set of CF parameters that fit the experimental levels as well as the low temperature Pr³⁺ magnetic moment in PrMnO₃ has been determined.     

Zeeman effect of the 6011 Å line of Pr3+: LaCl3 using the fluorescence line-narrowing technique

The Zeeman effect of the 6011 Å resonance line of Pr³⁺ in a LaCl₃ crystal has been studied by means of the fluorescence line-narrowing technique using a cw single-mode tunable laser. The experiments have confirmed the assumptions made previously to interpret the spectra in zero magnetic field. They have led to accurate values of the hyperfine structure constant and of the spectroscopic splitting g-factor of the ground level.     

Satellite lines in the optical absorption spectra of doped (La,Pr)Cl3-crystals

By substitution of an impurity ion, A³⁺, for a trivalent La³⁺-ion, symmetric and asymmetric distortions may be produced in the lattice of the anhydrous lanthanum trichloride. In LaCl₃ doped with Pr³⁺-ions at very low concentrations, these distortions give rise to Pr³⁺ satellite levels, the energy shift and Zeeman effect of which are calculated in a first order approximation. A survey is given of the possible types of single and double perturbations produced by substitution of one or two impurity ions in the neighbourhood of a non-Kramers ion in a hexagonal lattice of the LaCl₃-type. The results are quite general for non-Kramers rare-earth ions on hexagonal sites in any other lattices.Project of the Sonderforschungsbereich 65 Festkörperspektroskopie Darmstadt-Frankfurt, supported by the Deutsche Forschungsgemeinschaft     

Ultraviolet sum-frequency generation utilizing optical pair interactions in solids

We report the first observation of nonlinear generation of broadband ultraviolet light by pair interactions in a solid. Emission from PrF₃ on numerous features between 270–410 nm is ascribed to transitions of coupled atoms. They occur at sum-frequencies of known Pr³⁺ intraconfigurational transitions and show quadratic dependence on input power. High intensities and structured excitation spectra are observed. The prospect of stimulated ultraviolet pair emission with visible light excitation is examined.     

Luminescence of Pr3+-Activated fluorides

The strong dependence of the emission spectrum of YF₃:Pr³⁺ on excitation source (228.8 nm, 213.9 nm or cathode rays) is ascribed to two different types of Pr³⁺ sites: one with a relatively strong crystal field and the other with a relatively weak crystal field. The presence of the latter is connected with the conversion of one short-wave UV (? 215 nm) photon into two visible photons. Two-photon luminescence of Pr³⁺ was also found for α-NaYF₄ and LaF₃, but not for CaF₂ and BaF₂ due to the too strong crystal field in these lattices. The occurrence of two-photon Pr³⁺ luminescence is compared with the intensity of the IR-excited green emission of the corresponding Yb³⁺, Er³⁺-activated lattices. The intensity of the Pr³⁺ luminescence at shortwave UV excitation (213.9 nm) is rather weak. Luminescence of reasonable efficiency is, however, observed on excitation with cathode rays.     

Crystal field analysis of the absorption spectra and electron-phonon interaction in Ca3Sc2Ge3O12:Ni

Exchange charge model of crystal field [B.Z. Malkin, in: A.A. Kaplyanskii, B.M. Macfarlane (Eds.), Spectroscopy of Solids Containing Rare-earth Ions, North-Holland, Amsterdam, 1987, pp. 33-50.] was used to analyze the energy level schemes of Ni²⁺ ion at both possible positions (octahedral and tetrahedral) in Ca₃Sc₂Ge₃O₁₂. The crystal field parameters were calculated from the crystal structure data; the crystal field Hamiltonian was diagonalised in the complete basis consisting of 25 wave functions of all LS terms of the Ni²⁺ ion. Results of calculations are in a good agreement with experimental data. From the experimental spectra available in the literature, the Huang-Rhys parameter S=3.5 and effective phonon energy were evaluated for the octahedral Ni²⁺ ion.     

Influence of the ground state of the Pr<Superscript>3+</Superscript> ion on magnetic and magnetoelectric properties of the PrFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> multiferroic

The magnetic, magnetoelectric, and magnetoelastic properties of a PrFe₃(BO₃)₄ single crystal and the phase transitions induced in this crystal by the magnetic field are studied both experimentally and theoretically. Unlike the previously investigated ferroborates, this material is characterized by a singlet ground state of the rare-earth ion. It is found that, below T _N = 32 K, the magnetic structure of the crystal in the absence of the magnetic field is uniaxial (l ∥ c), while, in a strong magnetic field H ∥ c (H _cr ～ 43 kOe at T = 4.2 K), a Fe³⁺ spin reorientation to the basal plane takes place. The reorientation is accompanied by anomalies in magnetization, magnetostriction, and electric polarization. The threshold field values determined in the temperature interval 2–32 K are used to plot an H-T phase diagram. The contribution of the Pr³⁺ ion ground state to the parameters under study is revealed, and the influence of the praseodymium ion on the magnetic and magnetoelectric properties of praseodymium ferroborate is analyzed.     

Crystal field and spectrum of Pr4+ in BaPrO3

We have measured the absorption spectrum of BaPrO₃ in the spectral range 1900–11000 cm⁻¹. All the energy levels of the 4f electronic configuration of the Pr⁴⁺ ion in a crystal have been observed for the first time. We describe the total set of electron-nuclear states and the integral intensities of the magnetic dipole transitions of the Pr⁴⁺ in BaPrO₃ in the framework of the crystal field approximation. The crystal field parameters corresponding to the real orthorhombic symmetry of BaPrO₃ are obtained with the exchange charge model.     

Luminescence of Cs2NaScCl6:Pr3+: Effects of Changing the Elpasolite Lattice Parameter

Abstract

The luminescence spectrum of Cs₂NaScCl₆:Pr³⁺ (0.1 at.%) has been recorded at temperatures down to 10 K and assigned between 20,800 and 9900 cm^?1. Twenty‐three energy levels of the 4f² configuration Pr³⁺ ion were located and then fitted by the conventional 4f² crystal field calculation, as well as by a configuration interaction assisted crystal field (CIACF) calculation. The latter gave a much better fit. A comparison of the fit for Cs₂NaScCl₆:Pr³⁺ with fits upon the same set of energy levels in Cs₂NaYCl₆:Pr³⁺ and Cs₂NaPrCl₆, where the fifth nearest neighbor of Pr³⁺ is changed and the lattice parameter increases along this series, shows a decrease in the magnitudes of the crystal field parameters, which were also semiquantitatively simulated. Several facets of the emission spectra are interesting, including the observation of weak progressions in the totally symmetric Pr–Cl stretching vibration and the occurrences of the resonance of electronic and vibronic states. The spectra of Cs₂NaScCl₆:Pr³⁺ (1 at.%) differ considerably from those of the more dilute system and show that other species are formed rather than a complete substitution of the Sc³⁺ sites by Pr³⁺.     

Magnetische Eigenschaften von wasserfreiem Cer- und Praseodymchlorid

The results of susceptibility measurements on single crystals of anhydrous CeCl₃ and PrCl₃, published in a preceeding paper, are analysed in terms of a static crystalline electric field of approximate D_3h symmetry acting upon the Ce³⁺ and Pr³⁺ ions. For each of the two salts a set of crystal field parameters V ₂ ⁰ , V ₄ ⁰ , V ₆ ⁰ , V ₆ ⁶ was adjusted to fit the susceptibility data. To get agreement within experimental accuracy a small reduction of the Landég _J-factors had to be introduced, indicating the influence of factors which are omitted in the simple crystal field model, presumably covalent bond and configurational interaction.     

Comparative analysis of energy-level splitting of Pr3＋ doped in LiYF4 and LiBiF4 crystals： a complete energy matrix calculation

Based on the combination of Racah's group-theoretical consideration with Slater's wavefunction, a 91 × 91 complete energy matrix is established in tetragonal ligand field D_2d for Pr³⁺ ion. Thus, the Stark energy-levels of Pr³⁺ ions doped separately in LiYF₄ and LiBiF₄ crystals are calculated, and our calculations imply that the complete energy matrix method can be used as an effective tool to calculate the energy-levels of the systems doped by rare earth ions. Besides, the influence of Pr³⁺ on energy-level splitting is investigated, and the similarities and the differences between the two doped crystals are demonstrated in detail by comparing their several pairs of curves and crystal field strength quantities. We see that the energy splitting patterns are similar and the crystal field interaction of LiYF₄:Pr³⁺ is stronger than that of LiBiF₄:Pr³⁺.     

Spectroscopic analysis of Pr3+:CaYAlO4 crystal

The polarized absorption, emission spectra and decay time measurements of Pr³⁺-doped CaYAlO₄ single crystal have been performed at room temperature. Based on the Judd–Ofelt theory, the spectroscopic parameters \(\Upomega_{t} (t = 2,4,6)\) , radiative transition probabilities, radiative lifetimes and branching ratios were obtained. The stimulated emission cross-section, fluorescence lifetimes and the quantum efficiency of the promising laser transition were also calculated and compared with other reported crystals. The results show that Pr³⁺:CaYAlO₄ is a promising candidate for visible solid-state laser emission.     

Spectroscopic properties of Pr 3+ in anisotropic PbWO4 crystal

The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of Pr³⁺ ions in anisotropic PbWO₄ single crystal, which was grown by the modified Bridgman method, were measured at room temperature. The standard and modified Judd–Ofelt theories, extended to anisotropic crystal, have been applied to analyze the spectra. The spectroscopic parameters, including the Judd–Ofelt intensity parameters _t(t=2,4,6), spontaneous emission probabilities, fluorescence branching ratios, radiative lifetimes, stimulated emission cross sections, and fluorescence quantum efficiencies, were estimated. The good spectroscopic properties show the possible application of the Pr³⁺-doped PbWO₄ crystal as solid-state and self-stimulated Raman laser materials. PACS 78.20.-e; 42.70.Hj