Optical study of praseodymium dicarboxylate [Pr(H2O)]2[O2C(CH2)3CO2]3.4H2O

Praseodymium dicarboxylate, [Pr(H₂O)]₂[O₂C(CH₂)₃CO₂]₃.4H₂O]–glutarate, Pr[glut], is synthesized by hydrothermal techniques. The title compound crystallizes in the monoclinic space group C2/c (No. 15). The rare earth cation is coordinated by nine oxygen atoms, eight oxygen atoms from the carboxylate groups and one from the water molecule. The local symmetry of Pr site is low, C_s. The absorption spectra of Pr[glut] are recorded from the visible to the far IR domain at 300, 77 and 9 K. Under various Ar⁺ laser excitations no emission is detected from ³P₀ and ¹D₂ excited levels of Pr³⁺ ion. In the low temperature absorption spectra only one electronic line is recorded for ³H₄→³P₀ transition. It confirms a unique local environment for the rare earth ion in Pr[glut]. The utility of the ‘barycenter curves’ in the attribution of electronic lines is demonstrated. Energy level scheme of 36 Stark components is deduced from the absorption spectra. The parametric calculation was performed on the whole 4f² (Pr³⁺) configuration with the starting set of crystal field parameters obtained previously for the Eu³⁺ ion in the isostructural compound. Eight free ion and nine phenomenological crystal field parameters in C_2v symmetry reproduce quite well several electronic levels of Pr³⁺ ion experimentally observed in Pr[glut]. A good r.m.s. standard deviation of 14.8 cm⁻¹ is obtained.     

Optical study of a new phase LaGa3O6:RE (RE=Pr, Nd, Eu) in the La2O3–Ga2O3 system

The absorption and emission spectroscopies of RE³⁺ ions embedded in a new phase, LaGa₃O₆, owing to the La₂O₃–Ga₂O₃ binary system (RE=Pr, Nd, Eu) are discussed. The ^2S+1L_J level degeneracies are completely lifted in accordance with the low point symmetry of the site occupied by the rare earth ion in LaGa₃O₆. The energy level schemes deduced from the data are reproduced by considering a crystal field (CF) effective Hamiltonian involving the nine real and five imaginary parameters required for the C₂ or C_s symmetry of the rare earth site. The rms deviation is satisfactory for the three simulations. However, the strong variation of the CF parameters between Pr³⁺ and Eu³⁺ in LaGa₃O₆ suggests the possible limit of existence of the phase, intimately correlated to small variations of the rare earth ionic radius.     

Simulation of the crystal field effect on the Pr ion in K2La1−xPrxCl5 ternary chlorides

The high resolution absorption, luminescence and excitation spectra of the orthorhombic potassium lanthanum praseodymium ternary chloride, K₂La_1−xPr_xCl₅, (0.02 ≤ x ≤ 0.15) single crystals were recorded at 4, 77 and 293 K with different excitation sources. The experimental 4f² energy level scheme of the Pr³⁺ ion in K₂LaCl₅ derived from the absorption and emission spectra consisted of 86 (out of 91) Stark components. This energy level scheme was simulated by using a phenomenological crystal field (cf) model which included eight free ion and nine cf parameters according to the C_2v symmetry. Despite the approximate C_2v point symmetry instead of the real C_s one, the simulation yielded a very satisfactory rms deviation of 17 cm⁻¹ between the experimental and calculated energy level schemes. The results, especially the weak cf strength, are discussed taking into account the bonding characteristics in K₂LaCl₅.     

Spectroscopic study of europium doped RCOB host lattices: evidence of local perturbations

The results of the high-resolution absorption, selective excitation, time-resolved emission and emission kinetics of Eu³⁺ in GdCOB and EuCOB single crystals are presented. The Eu³⁺ spectra show at least three non-equivalent centers whose static spectral characteristics were used to assign structural models. The crystal field parameters were estimated for prevailing Eu³⁺ center in EuCOB. The inhomogeneous broadening and shifts of the ⁵D₀→⁷F₀ and ⁵D₀→⁷F₁ Eu³⁺ lines in GdCOB under selective excitation in main lines were explained by J mixing of ⁷F₂ states into ⁷F₁ and ⁷F₀ by second order crystal field terms and connected to disordered structure in cationic spheres.     

Crystal fields in (La1−xGdx)OCl:Eu solid solutions

The formation of cation solid solution in the (La_1−xGd_x)OCl:Eu³⁺ (0≤x_Gd≤1; Δx_Gd=0.1) series was studied by photoluminescence spectroscopy. The luminescence from the ⁵D_0–2 to the ⁷F_0–4 levels of the Eu³⁺ ion in the (La_1−xGd_x)OCl series was recorded at 77 K by using argon ion laser excitation (457.9 nm). The interpretation of the spectra according to the C_4v site symmetry of the Eu³⁺ ion in the tetragonal PbFCl-type structure yielded nearly complete sets (18 to 19 levels) for the ⁷F_0–4 levels. Simulations of the Stark level schemes were carried out with the aid of a phenomenological c.f. theory utilizing the five non-zero c.f. B_q^k parameters (B₀², B₀⁴, B₄⁴, B₀⁶ and B₄⁶) allowed for the C_4v site symmetry. By using the calculated c.f. parameter sets a quantitative measure was obtained to monitor the formation of cation solid solutions. The strength of the c.f. effect was estimated with the c.f. strength parameters S and S^k (k=2, 4 and 6). The c.f. parameter sets reproduced the experimental ⁷F_J (J=0–4) energy level schemes with the rms deviations between 4 and 11 cm⁻¹. The individual parameters as well as the c.f. strength parameters were found to evolve in a smooth manner indicating complete solid solubility in the (La_1−xGd_x)OCl series. Some local distortions from the C_4v symmetry — probably of long range—leading to the splitting of the ⁷F₁ doubly degenerate E level were observed, however.     

Optical absorption spectrum, oscillator strengths, magnetic splitting factors and paramagnetic susceptibility of Nd doped into LiYO2

Optical and magnetic measurements are performed on Nd³⁺ doped into LiYO₂. 105 energy levels of Nd³⁺ are assigned from the optical absorption and excitation spectra for the powdered sample at 20 K. The crystal field analysis is performed in the C₁ site symmetry of Nd³⁺. Theoretical values of the crystal field parameters, oscillator strengths, magnetic susceptibility and ground state splitting factors are calculated and compared with experimentally measured quantities.     

The reduction of Eu to Eu in air and luminescence properties of Eu activated ZnO–B2O3–P2O5 glasses

A valence change from Eu³⁺ to Eu²⁺ was observed in the europium ion-doped ZnO–B₂O₃–P₂O₅ glasses prepared at high temperature in air. The fluorescence emission spectrum of the sample consists of a broad emission band ascribed to the 5d–4f transition of Eu²⁺ ion and sharp emission peaks assigned to the transitions of ⁵D_o–⁷F_J (J = 0, 1, 2, 3, and 4) of Eu³⁺ ion, indicating that part of Eu³⁺ can be reduced into Eu²⁺ in the glass. A charge compensation model is proposed. The rigid tetrahedral network structure of glasses plays an important role in stability of Eu²⁺. The fabrication conditions are also studied.     

Preparation of nanocrystalline Lu2O3:Eu phosphor via a molten salts route

The paper reports on the course of decomposition of hydrated lutetium nitrate and lutetium chloride to Lu₂O₃ in the eutectic mixture of NaNO₂ and KNO₂. It was shown that a crystallographically pure phase of the cubic Lu₂O₃ is formed at temperature as low as 250 °C. IR spectra revealed that the recovered powder contains some OH-contamination, however. The powders are characterized by crystallites sizes in the range of 18–30 nm in average. Emission and excitation spectra of Eu-doped powders show characteristic features for Eu³⁺ ion in an oxide host, which indicates that the procedure is appropriate for making activated nanoparticulate oxide phosphors. Most profound emission appears around 611 nm and the luminescence from the powder made starting with Lu(NO₃)₃ was noticeably higher compared to the product obtained from LuCl₃. The excitation spectrum of Eu³⁺ emission at 611 nm contains a band related to the fundamental absorption of the lutetia host lattice, which indicates an existence of the host-to-activator energy transfer.     

Synthesis of SrAl2O4：Eu^2＋,Dy^3＋ phosphors by the coupling route of microemulsion with coprecipitation method

Nano-sized SrAl2O4：Eu^2＋,Dy^3＋ phosphors with good monodispersity and narrow size distribution were synthesized by the coupling of water-in-oil （W/O） microemulsion with coprecipitation method. The phase composition, morphology, crystallinity, excitation spectra, emission spectra, and afterglow decay of SrAl2O4：Eu^2＋,Dy^3＋ nanophosphors were measured. It was found that the amount of surfactant that was used had an important effect on the shape and average size of the phosphor particles. SrAl204 phase of the phosphors showed an increase with the increase in calcination temperature. When the calcination temperature reached 1150℃, the fine crystal of SrAl2O4 was formed and the long afterglow luminescence could be obviously observed. In comparison with the samples prepared by the high-temperature solid-state method, the calcination temperature showed an obvious decrease and a dear blue shift occurred in the excitation and emission spectra of the sample. The afterglow time could be more than 8 h.     

Effect of Zn and Li codoping ions on nanosized Gd2O3:Eu phosphor

Nanosized Gd_1.92−x−yZn_xLi_yEu_0.08O_3−δ phosphor was fabricated by combustion synthesis. The effect of Zn²⁺ and Li⁺ ions on the crystallization behavior, morphology, and luminescence property of Gd₂O₃:Eu³⁺ was investigated. The results indicated that incorporation of Zn²⁺ and Li⁺ ions into Gd₂O₃:Eu³⁺ nanoparticles (NPs) could lead to a remarkable increase of photoluminescence or X-ray excited luminescence, and the intensity at 612 nm was increased by a factor of 7.1 or 21.5 in comparison with that of undoped sample. The enhanced luminescence was regarded as the results of the creation of oxygen vacancies due to the Gd³⁺ sites occupied by Li⁺ ions, the alteration of the crystal field surrounding the activator Eu³⁺ ions owing to the incorporation Zn²⁺ ions into interstitial sites, and the flux effect of Zn²⁺ and Li⁺ ions. The Zn- and Li-codoped Gd₂O₃:Eu³⁺ phosphor with highly enhanced luminescence is very encouraging for applications in high-resolution display devices.     

Optical properties and crystal field calculations of europium tellurium oxide

Absorption and fluorescence measurements have been performed on pure Eu₂Te₄O₁₁ tellurium oxide and on Eu³⁺-doped Gd₂Te₄O₁₁ samples. The spectra were recorded at liquid helium, liquid nitrogen and room temperatures. In this monoclinic host matrix, the rare earth occupies a single crystallographic point site, with the very low symmetry C₁. The energy level scheme is derived, from the experimental data, for the ⁷F_j (J= 0,1,2,3,4) ground multiplet of the 4f⁶ configuration of Eu³⁺. Despite the low symmetry for the rare earth, parametrization of the crystal field effects was carried out with very good r.m.s. standard deviations and residues.     

Structure and properties of the KNbW2O9 hexagonal bronze doped with Eu ions as an optically active probe

Luminescence properties of KNbW₂O₉ crystal doped with Eu³⁺, investigated at room and liquid nitrogen temperatures, showed that the active ions occupy two crystallographically different sites. The structural and IR spectra investigations were also carried for better understanding of Eu³⁺ ion behavior. The luminescence decay profiles were slightly non-exponential. The luminescence lifetimes of Eu³⁺ were approximated by biexponential decays. Both were ascribed to two different Eu(III) sites. The longer component was determined to be ca. 1 ms, whereas the shorter one was about 0.5 ms. It was found that the Eu sites characterized by longer decay times were not affected by temperature, whereas the sites characterized by shorter decay times revealed strong decrease of decay times with temperature. Infrared investigation demonstrated the presence of water molecules occupying hexagonal tunnels in the KNbW₂O₉ crystal. The UV irradiated crystal showed the presence of blue coloration. The observed color was attributed to small W⁵⁺ polarons or intervalence charge transfer between W⁵⁺ and W⁶⁺ states. The electrons, necessary for the formation of the W⁵⁺ states, originate most likely from UV photodissociation of water molecules.     

The electronic structure of organometallic complexes of the f elements XLI: Crystal field strength of η-cyclooctatetraenyl ligand estimated on the basis of the preliminary crystal field parameters of (COT)Nd[HB(3,5-Me2pz)3]

The absorption spectrum of (η⁸-COT)Nd[HB(3,5-Me₂pz)₃] (COT=cyclooctatetraenyl, pz=pyrazol-1-yl) has been measured at room temperature, at approximately 90 K and in parts at ca. 30 K. The bands were assigned by applying the selection rules for C_8v symmetry and by performing crystal field (CF) calculations assuming the CF parameters of the Nd complex were the same as for the previously analyzed (COT)Pr[HB(3,5-Me₂pz)₃]. The parameters of an empirical Hamiltonian were fitted to the energies of 27 levels to give an r.m.s. deviation of 25.5 cm⁻¹. Neglecting the influence of [HB(3,5-Me₂pz)₃] ligand, the CF strength of the [COT]⁻⁻ ligand could be estimated from the CF parameters obtained.     

Optical absorption and spectroscopic characteristics of Tm ions doped NaY(MoO4)2 crystal

The polarized absorption and emission spectra have been measured for the Tm³⁺ doped NaY(MoO₄)₂ crystal and spectral parameters have been estimated from the absorption data based on the Judd–Ofelt theory. The effective intensity parameters (t = 2, 4, 6) are 11.67 ×10⁻²⁰, 2.21 × 10⁻²⁰, 1.74 × 10⁻²⁰ cm², respectively. From the intensity parameters, the radiative transition probabilities, radiative lifetimes, branching ratios and the emission cross-section have been calculated. In comparison with other Tm³⁺ doped laser crystals, Tm³⁺:NaY(MoO₄)₂ crystal has potential as a promising laser crystal.     

Absorption and magnetic circular dichroism spectra of praseodymium doped fluorozirconate (ZBLAN) glass

Optical absorption and magnetic circular dichroism (MCD) spectra of 1% Pr³⁺ doped ZBLAN fluorozirconate glass have been recorded at several temperatures between 4.2 K and room-temperature. The dipole strengths of the 4f–4f transitions are parametrized in terms of three phenomenological Judd–Ofelt intensity parameters Ω_λ (λ=2, 4 and 6). The method of moments was used to extract the Faraday parameters from the MCD spectra. While the room-temperature MCD spectra are dominated by A-terms (which have the shape of the first derivative of an absorption curve), C-terms become more important at lower temperature. The temperature dependence of the ³P₀←³H₄ transition is a typical example. The temperature dependent change of the MCD spectrum can be explained by the differential thermal population of the Zeeman levels from which absorption of left and right circularly polarized light takes place.     

The size-effect on luminescence properties of BaTiO3:Eu nanocrystallites prepared by the sol–gel method

Luminescence investigations of nanocrystalline (nc) BaTiO₃ powders doped with Eu³⁺-ions prepared by the sol–gel method is described. A stability of Eu³⁺-ions replacing Ba²⁺-sites up to 1100 °C is reported. The effect of BaTiO₃ grain sizes on luminescence properties of Eu³⁺ was noticed. To explain these differences a detailed analysis of luminescence spectra by the Judd–Ofelt theory has been performed.     

Crystal fields in ROF:Tb (R = La, Gd)

Laser excited luminescence and site selective excitation spectra of trivalent terbium (Tb³⁺) in two rare earth oxyfluoride (ROF) matrices, LaOF and GdOF, were detected at temperatures down to liquid helium. From the analyses of spectra, the crystal field (c.f.) fine structure of the ⁷F_J (J=0–6) ground multiplet was obtained for the 4f⁸ electron configuration. The energy level schemes comprising 26 c.f. sublevels out of 33 allowed for the C_3v point symmetry of the R³⁺ site were simulated according to a phenomenological model taking into account only the c.f. effect.

The simulation including six c.f. parameters (B₀², B₀⁴, B₃⁴, B₀⁶, B₃⁶, and B₆⁶) reproduced the experimental energy level schemes in a satisfactory manner with rms deviations of 5 and 6 cm⁻¹ for the LaOF and GdOF hosts, respectively. The c.f. parameter sets are characterized by B₀² values close to zero while the fourth and sixth rank parameters assumed rather high values. The O_h to C_3v descending symmetry method revealed a slight trigonal distortion from the cubic fluorite CaF₂-type structure. The c.f. parameters vary only slightly as a function of the host matrix. The ⁷F₆ level was not simulated correctly probably because of the electron–phonon interaction.     

Kinetic and spectral aspects in chemiluminescence system Eu(III)/HCO3/H2O2

Chemiluminescence (CL) of the systems containing Eu₂⁺ or HCO₃⁻ ions and hydrogen peroxide was studied. The kinetic curves and CL emission spectra of the systems were discussed. The emission spectrum of the system containing carbonates revealed two emission maxima: the first directly after initiation of the reaction by hydrogen peroxide and the second in several seconds after the first. On the basis of the characteristic bands in the CL spectrum the emitters in the system Eu₂⁺/HCO₃⁻/H₂O₂ were identified as: excited Eu³⁺ ions and excited products of carbonate decomposition. The emission bands for λ=600 and 420 nm appeared in a time distance of a few ten seconds.     

Structural chemistry and magnetism of dicyclopentadienidehalides of lanthanides Part 8: terbiumdicyclopentadienidebromide [Tb(C5H5)2Br]2

A single-crystal X-ray structural investigation of [Tb(C₅H₅)₂Br]₂ revealed the [Sc(C₅H₅)₂Cl]₂-type structure, space group P2₁/c, with a = 1407.6(2) pm, b = 1644.7(2) pm, c = 1370.6(9) pm, β = 93.46(3)°, V = 3167(2) × 10⁶ pm³, D_c = 2.322 g cm⁻³ and Z = 6 dimers (R = 0.036 for 4627 reflections with I > 3σ(I)). The metal centres have the pseudosymmetry C_2v. Magnetic susceptibility data show Curie-Weiss behaviour between 213 and 6 K with θ_p = −4.5(3) K and a magnetic moment μ = 9.8(1) μ_B close to the Tb³⁺ free-ion value (9.72 μ_B). Below 6 K, deviations from Curie-Weiss behaviour are observed, and at 5.3 K a maximum in the susceptibility is detected which may be caused by intradimer antiferromagnetic spin coupling. The magnetic properties are compared with the prediction of various models, starting from cubic crystal fields and isotropic intramolecular exchange interactions, followed by extension to lower crystal field symmetry (orthorhombic) and anisotropic contributions to the spin coupling. However, a reasonable agreement between the measured and calculated data was not obtained. As in [Gd(C₅H₅)₂Br]₂, the low-temperature behaviour is governed by effects which cannot be described by spin coupling models in the generally accepted form.     

Luminescence and energy migration in the oxyapatite Ca2Gd8(SiO4)6O2 doped with several rare earth and mercury-like ions

Energy transfer phenomena have been observed by activating the oxyapatite host-lattice Ca₂Gd₈(SiO₄)₆O₂ with Eu³⁺, Tb³⁺, Dy³⁺, Sm³⁺. This is based on the energy migration in the Gd³⁺ sublattice and trapping by the activators. The trapping efficiency for Gd³⁺ excitation energy increases in the sequence of Sm³⁺ < Dy³⁺ < Tb³⁺ < Eu³⁺. It is supposed that the activator ions are incorporated on both Gd³⁺ sites in Ca₂Gd₈(SiO₄)₆O₂. The Gd³⁺ sublattice in Ca₂Gd₈(SiO₄)₆O₂ can be sensitized by Pb²⁺ but not by Ce³⁺, Pr³⁺ and Bi³⁺.