Local probe (170Yb3+) measurements of magnetic fields in YBa2Cu3Ox

We introduce the technique of studying the field dependence of the electro-nuclear energy levels of a rare earth to measure the magnetic field present at the rare earth/yttrium site in YBa₂Cu₃O_x. Measurements were made by¹⁷⁰Yb Mössbauer spectroscopy. The hyperfine spectrum of the ground state Kramers doublet for Yb³⁺ ions diluted into this matrix is sensitive to fields in the range 100 to 2000G. Flux penetration and trapping at the local site level have been measured in superconducting samples. A molecular field exists on the rare earth site in non superconducting samples suggesting that the ordered Cu2 magnetic moments are intrinsically non colinear.     

Mössbauer measurements on170Yb3+ substituted into YBa2Cu3O7

We present some results obtained by Mössbauer spectroscopy on Yb³⁺ when substituted into YBa₂Cu₃O _x -like compounds. For the fully substituted compound YbBa₂Cu₃O₇, we describe the properties of the rare earth sublattice magnetic ordering which coexists with superconductivity. From measurements at the dilute substitution level, we study the Yb³⁺ crystal field properties and the thermal dependence of the Yb³⁺ paramagnetic relaxation rate. By making use of the molecular field produced on the Yb³⁺ probe by the magnetically correlated Cu(2), we examine the evolution of the Cu(2)-based magnetism as a function of carrier density and study the phase separation which occurs in the superconducting samples with intermediate oxygen levels. We also examine how the properties of the Yb³⁺ probe are influenced by the substitution of Pr³⁺ or Zn²⁺ (these substitutions are known to considerably influence the superconducting properties).     

Relationship between charge transfer energies of Yb and Sm and crystal environmental factor

Relationship between charge transfer energies E_CT of Yb³⁺ and Sm³⁺ and environmental factors h_e in various crystals was investigated using a dielectric chemical bond method. Both results show that they have an exponential relation E_CT=A+B exp(−kh_e), but the exponential factors are different, which indicates that the interaction between the rare earth ions and environment is connected with the kind of rare earth ion. This result provides a method of determining charge transfer energies of Yb³⁺ and Sm³⁺ from a crystal structure.     

Arrays of micro-cavities activated with laser ions

We have combined different rare earth ions (Er³⁺, Nd³⁺ and Yb³⁺) in two dimensional ferroelectric patterns to obtain periodical fluorescent arrays. High refractive-index Er³⁺ doped CaTiO₃ nanocrystals have been embedded into Nd³⁺ or Yb³⁺ doped LiNbO₃ substrates pre-patterned with a two dimensional arrays of micro-voids. The process of incorporation and consolidation of the optically active nanoparticles into the alternate domain structures leads to luminescent ring-shaped arrangements with innovative geometries and to a micrometer spatial control of the trivalent rare earth ion emitters. Multicolor emission systems and the possibility of chromatic switching at the micrometer scale among the different compounds forming the two dimensional structure is demonstrated.     

Analysis of hyperfine structure of Rare‐Earth Ions in Single Crystals by Electron Paramagnetic Resonance Spectroscopy

Electron paramagnetic spectroscopy of rare‐earth ions in single crystals is an interesting tool to analyze the hyperfine structure of the ground state of the rare‐earth. This can be useful for coherent spectroscopy and quantum information applications where the hyperfine structure of the electronic levels is used. Moreover, in some cases, the electron paramagnetic resonance hyperfine structure of interacting rare‐earth ions allows us to retrieve the isotropic exchange interaction between the two interacting ions. We illustrate these points with the hyperfine structure of Yb³⁺ ions in vanadate crystals, the hyperfine structure of Er³⁺ ions in Y₂SiO₅, and the hyperfine structure of Yb³⁺ pairs in CsCdBr₃.     

Magnetic properties of YbNi5 from 170Yb Mössbauer and magnetisation measurements

From Yb¹⁷⁰ M?ssbauer measurements on YbNi₅, we establish: the Yb³⁺ ground state Kramers doublet is well isolated and has uniaxial anisotropy, the compound magnetically orders at 0.55 K, the Yb³⁺ moments are aligned along the hexagonal axis, they have a saturated value of 3.9μ_B and a thermal variation close to a mean field S = 1/2 law. We obtain the strength of the Yb³⁺–Yb³⁺ coupling which we find is considerably smaller than that between the rare earths (R³⁺) in the other RNi₅. From a study of the spin dynamics, we find that dynamic short range order is present just above the ordering temperature and that above 2 K, the relaxation rate of the paramagnetic Yb³⁺ spins follows a T-linear Korringa law with a relatively pronounced slope which we link to a high density of states at the Fermi level. Magnetic susceptibility and magnetisation measurements establish the ferromagnetic nature of the Yb³⁺–Yb³⁺ coupling. We comment on the Yb³⁺ crystal field properties.     

Charge transfer transitions and location of the rare earth ion energy levels in Ca-α-SiAlON

The broad bands in the room-temperature excitation spectra of Sm³⁺-, Dy³⁺- and Tm³⁺-activated Ca-α-SiAlON phosphors are interpreted as the N³⁻-to-rare earth charge transfer transition (CTT). From the energies of the charge transfer transitions and from the optical data presented for the Eu²⁺ ion, the location of the divalent rare earth ion energy levels relative to the valence and the conduction band of Ca-α-SiAlON is derived. The salient features of the energy-level diagram are shown to be practical in explaining the temperature-dependent variations of the Eu²⁺ and Yb²⁺ luminescence efficiency in Ca-α-SiAlON. A comparative study pertaining to the nature of the Yb²⁺ and Eu²⁺ ion luminescence in Ca-α-SiAlON and in SrSi₂O₂N₂ is presented. A tentative energy-level diagram of the trivalent rare earth ions in Ca-α-SiAlON is also constructed.     

Effect of Yb3+ concentration on photoluminescence properties of cubic Gd2O3 phosphor

Yb³⁺ doped phosphor of Gd₂O₃ (Gd₂O₃:Yb³⁺) have been prepared by solid state reaction method. The structure and the particle size have been determined by X-ray powder diffraction measurements. The average particle size of the phosphor is in between 35 and 50 nm. The particle size and structure of the phosphor was further confirmed by TEM analysis. The visible and NIR luminescence spectra were recorded under the 980 nm laser excitation. The visible upconversion luminescence of Yb³⁺ ion was due to cooperative luminescence and the presence of rare earth impurity ions. The cooperative upconversion and NIR luminescence spectra as a function of Yb³⁺ ion concentration were measured and the emission intensity variation with Yb³⁺ ion concentration was discussed. Yb³⁺ energy migration quenched the cooperative luminescence of Gd₂O₃:Yb³⁺ phosphor with doping level over 5%, while the NIR emission luminescence continuously increases with increasing Yb³⁺ ion concentration.     

Tm,Yb掺杂五磷酸盐非晶中的上转换蓝光发射

报道在室温下，高浓度Tm和高浓度Yb掺杂的五磷酸盐非晶在966nm半导体激光器激发下，Tm的¹G₄能级和⁴F₄能级分别产生峰位在480nm波长较强的上转换蓝光发射和很强的近红外780nm荧光发射．这一荧光发射是由于Yb的²F_5/2能级对966nm激光的强烈吸收，以及对Tm的相应上转换能级较强的能量传递而产生的上转换过程，Tm的浓度增大又使Tm的³F相似文献   

Influence of co-doping different rare earth ions on CaGa2S4: Eu, RE(RE=Ln) phosphors

Photoluminescent phosphors CaGa₂S₄: Eu²⁺, RE³⁺ (RE³⁺ including all rare earth ions except for Sc³⁺, Pm³⁺, Eu³⁺ and Lu³⁺) were prepared by sintering at high temperature in a reductive atmosphere, and their luminescent properties were studied intensively. The influences of co-doping rare earth ions on their luminescent properties were also investigated. No remarkable differences were found from excitation spectra of co-doped phosphors CaGa₂S₄: Eu²⁺, RE³⁺ in contrast with that of phosphor CaGa₂S₄: Eu²⁺, but there were a few differences in emission spectra of Ce³⁺, Pr³⁺ or Ho³⁺ co-doped phosphors. Phosphors CaGa₂S₄: Eu²⁺, RE³⁺ (RE=Ce, Pr, Gd, Tb, Ho and Y) had persistent afterglow, and very short afterglow was shown for Nd³⁺ or Er³⁺ co-doped phosphors, but no long afterglow appeared when auxiliary activator was La³⁺, Sm³⁺, Dy³⁺, Tm³⁺ or Yb³⁺. Among the phosphors with long-lasting phosphorescence, in our experiments, CaGa₂S₄: Eu²⁺, Ho³⁺ had the longest and the highest brightness long yellow afterglow. Thermo-luminescence of all co-doped phosphors was measured to find the answer of different influences from different rare earth auxiliary activators.     

The fluorescence of polyamidoamine dendrimers peripherally modified with 1,8-naphthalimide groups: Effect of the rare earth ions and protons

We report the absorption spectra, fluorescent spectra and photophysical properties of G 2.0 polyamidoamine dendrimers with peripheral 1,8-naphthalimide groups with the hydrogen ions, the rare earth ions (Er³⁺, Tb³⁺, Nb³⁺, Eu³⁺, Yb³⁺ and Gd³⁺) and the mixture of the rare earth metal and hydrogen ions. The presence of the rare earth ions and hydrogen ions was found to enhance the fluorescence owing to the coordination between the rare earth metal or hydrogen ions and internal amido groups of polyamidoamine (PAMAM) from dendrimer. The result from the 3D isogram of the fluorescence spectra for the dendrimers with peripheral 1,8-naphthalimide groups show that it was obtained for the different emission fluorescence intensity and scope by varying the excitation wavelength and the different rare earth ions as well as its concentration. The results obtained reveal that the capacities of these systems might have acted as a sensitive label agent of the rare earth cations and protons.     

Thermoluminescent properties of Eu and RE co-doped phosphors CaGa2S4:Eu, RE (RE=Ln, excluding Pm, Eu and Lu)

The thermo-luminescence (TL) of rare earth ions RE³⁺ (RE=Ln, excluding Pm, Eu and Lu) co-doped phosphors CaGa₂S₄:Eu²⁺, RE³⁺ was studied between room temperature and 300 °C, and 3D thermo-luminescence of the phosphors were measured from room temperature to 400 °C. The basic material CaGa₂S₄:Eu²⁺, showed at least two bands in the TL glow curve. Changing the auxiliary activator RE³⁺ (rare earth ion), intensities and the positions of the TL glow curve peaks were affected significantly. For the phosphors with long afterglow, auxiliary activator such as Ce³⁺, Pr³⁺, Gd³⁺, Tb³⁺, Ho³⁺, or Y³⁺ created some new defects in these compounds at lower trap levels and enhanced their TL intensities. The Nd³⁺ or Er³⁺ auxiliary activator only enhanced TL intensities to a low extent, so these two phosphors have short persistent luminescence at room temperature. TL intensities of La³⁺, Sm³⁺, Tm³⁺ or Yb³⁺ co-doped phosphors were suppressed greatly and no afterglow was shown. The relationship between auxiliary activators and corresponding thermo-luminescence curves of phosphors CaGa₂S₄:Eu²⁺, RE³⁺ are discussed in detail. According to our results, suitable activation energy and enough high corresponding trap density are necessary for the phosphor with long afterglow.     

Magnetic polarization of Yb3+ by Cu2+ in Yb2BaCuO5

The magnetic properties of Yb³⁺ in Yb₂BaCuO₅ have been examined using¹⁷⁰Yb Mössbauer spectroscopy. The quadrupole and magnetic hyperfine parameters of the Yb³⁺ ground doublet at each of the two sites have been obtained. The Yb³⁺ magnetic polarization is due uniquely to couplings with the ordered Cu²⁺ moments.     

Collisional relaxation of ionic2 P 3/2 excited states in rare gases

Optical pumping with theD ₂ line is used to study the depolarization of the first excited² P _3/2 states of alkaline earth ions and Yb⁺ ions in collisions with rare gas atoms. The deorientation cross sections for the even isotopes of Ba⁺ and Yb⁺ ions are obtained (in units of 10^?16 cm²): rare gas He Ne Ar Kr Xeσ ₁ (Ba⁺ 6p ² P _3/2) 79(11) 89(13) 123(18) 152(22) 204(30)σ ₁ (Yb⁺ 6p ² P _3/2) 60(10) 62(9) 107(18) 133(17) 167(37) The cross sections are discussed in comparison with theoretical calculations and those of isoelectronic atoms. The comparison of the² P _3/2 relaxation of even and odd (I=3/2) isotopes of Ba⁺ allows to draw conclusions on the nature of the depolarization interaction.     

Experiments and analysis of infrared quantum cutting luminescence phenomena of Ho/Yb codoped nanophase oxyfluoride vitroceramics

The infrared quantum cutting phenomenon, which is an international hot research field, of Ho³⁺Yb³⁺: oxyfluoride vitroceramics (FOV) was studied in the present paper. It was found from the fluorescence spectroscopy experiments that the excitation spectrum of 973.0 nm fluorescence of Yb³⁺ ion is very similar to the absorption and excitation spectra of Ho³⁺ ion. It suggests that the energy transfer from Ho³⁺ ion to Yb³⁺ ion is very efficient. Then, all the possible important energy transfer passages were analyzed. It was found that the energy transfers {⁵G₄(Ho³⁺)→⁵F₅(Ho³⁺), ²F_7/2(Yb³⁺)→²F_5/2(Yb³⁺)} and {⁵F₅(Ho³⁺)→⁵I₇(Ho³⁺), ²F_7/2(Yb³⁺)→²F_5/2(Yb³⁺)} result in the effective two-photon quantum cutting 973.0 nm fluorescence of Yb³⁺ ion when ⁵G₄ or ³K₇ or the above energy level of Ho³⁺ ion are excited. Finally, the quantum efficiency η_QE,1%Yb=43.0% and η_QE,5%Yb=171.7% of two-photon quantum cutting was calculated for Ho(0.5)Yb(1):FOV and Ho(0.5)Yb(5):FOV respectively. This research would be beneficial for the enhancement of solar cell efficiency.     

Microwave sol-gel process of KGd(WO4)2:Ho3+/Yb3 phosphors and their upconversion photoluminescence properties

Double tungstate KGd_1−x(WO₄)₂:Ho³⁺/Yb³⁺ phosphors with doping concentrations of Ho³⁺ and Yb³⁺ (x=Ho³⁺+Yb³⁺, Ho³⁺=0.05, 0.1, 0.2 and Yb³⁺=0.2, 0.45) were successfully synthesized by the microwave sol–gel method, and the upconversion mechanisms were investigated in detail. The synthesized particles formed after heat-treatment at 900 °C for 16 h showed a well crystallized morphology with particle sizes of 2–5 μm. Under excitation at 980 nm, the UC intensities of KGd_0.7(WO₄)₂:Ho_0.1Yb_0.2 and KGd_0.5(WO₄)₂Ho_0.05Yb_0.45 particles exhibited yellow emissions based on a strong 550-nm emission band in the green region and a strong 655-nm emission band in the red region, which were assigned to the ⁵S₂/⁵F₄→⁵I₈ and ⁵F₅→⁵I₈ transitions, respectively. The Raman spectra of the doped particles indicated the presence of strong peaks at higher frequencies of 764, 812, 904, 984, 1050, 1106, 1250 and 1340 cm⁻¹ induced by the disorder of the [WO₄]²⁻ groups with the incorporation of the Ho³⁺ and Yb³⁺ elements into the crystal lattice or by a new phase formation.     

Power factors of late rare earth-doped Ca3Co2O6 oxides

Polycrystalline samples of (Ca_1−xR_x)₃Co₂O₆ with R = Gd, Tb, Dy and Ho at x=0-0.1 were synthesized and the effects of rare earth substitution on their thermoelectric properties were investigated. In the high-temperature region, the rare earth substitution resulted in an increase in the Seebeck coefficients (S), and the S values increased with decreasing ionic radius of rare earth elements in the order Gd³⁺>Tb³⁺>Dy³⁺>Ho³⁺. In contrast, the influence of rare earth substitution on the electrical resistivity was small. The high-temperature power factor was thereby improved by the late rare earth substitutions, particularly those with Ho³⁺ for Ca²⁺. For the Ho-doped samples (x≤0.05), the power factor was significantly improved by increasing Ho concentration.     

Magneto-optical spectroscopy of Yb ions in huntite structure

We report the first measurements of magnetic circular dichroism (MCD) and magneto-optical activity (ratio of zero moments of MCD and absorption bands) of Yb³⁺ ion in the trigonal single crystals Yb_xTm_1−xAl₃(BO₃)₄ as a function of temperature in the range of 100-293 K. Magneto-optical activity follows the Curie-Weiss law with the Weiss constant θ=−55 K for Yb_0.1Tm_0.9Al₃(BO₃)₄ crystal. The value and origin of the magneto-optical activity is theoretically analyzed.     

Luminescent properties of Yb-doped monoclinic yttrium polyphosphates

Yb³⁺-doped monoclinic yttrium polyphosphate Y(PO₃)₃ powder compounds were synthesized and were characterized by X-ray diffraction, IR absorption spectroscopy and Raman scattering spectroscopy.An attempt to use Yb³⁺ ion as structural probe is carried out to investigate the site occupation. Yb³⁺ emission and fluorescence decay studies were carried out both at low and room temperatures. The interpretation of electronic energy level positions has been done by using the comparison of emission spectra with those of vibronic sideband energy positions from Raman scattering spectroscopy.The spectroscopic results are discussed and correlated with the data of the already known monoclinic structure of Y(PO₃)₃ where four slightly different octahedral sites are available for the trivalent rare earth ion.     

Lasing Yb<Superscript>3+</Superscript> in crystals with a wavelength dependence anisotropy displayed from La<Subscript>2</Subscript>CaB<Subscript>10</Subscript>O<Subscript>19</Subscript>

We report spectroscopic and laser properties for propagation directions outside the principal axes of Yb³⁺-doped low symmetry laser crystals with a special devotion to the wavelength dependence anisotropy. We illustrate our report with experimental data in the 900–1075 nm range of wavelengths from the Yb³⁺:La₂CaB₁₀O₁₉ monoclinic crystal excited under laser diode pumping at 975 nm. This study, which makes easier the realization of Yb³⁺ lasers with an efficient free-running operation at the wavelength having the highest emission intensity or at a specified wavelength, or emitting two frequencies with a specified frequency difference, is of promising interest for applications.