Divalent Yb Ions Research Articles

Near-Infrared Emission from CdSe-Based Nanoplatelets Induced by Ytterbium Doping

Cadmium selenide (CdSe) nanoplatelets (NPLs) have attracted significant attention thanks to their favorable optical properties, including narrow emission linewidths, reduced Auger recombination, and a high absorption cross section. However, the photoluminescence (PL) quantum yield (QY) in the near-infrared (NIR) region is poor as compared to that in the visible region. Doping of metal ions is proven to be a successful strategy for inducing Stokes-shifted NIR emission. Here, we report the first account of the successful doping of ytterbium (Yb) into CdSe NPLs by a modified seeded-growth method. The successful incorporation of divalent Yb ions into CdSe NPLs resulted in an additional NIR emission apart from their excitonic emission. By optimizing the dopant concentration, we observed an impressive PL QY of ∼55% for these Yb-doped NPLs. Detailed elemental and optical characterizations were conducted to understand the emerging photophysical properties of these Yb-doped NPLs. These NIR-emitting lanthanide-doped CdSe NPLs might have applications in the next-generation bioimaging, night vision, and photodetection.

Thermal and electron transport studies on the valence fluctuating compound YbNiAl4

We report the thermoelectric power S and thermal conductivity κ measurements on the valence fluctuating compound YbNiAl4, furthermore taking into account the impact of the applied magnetic field. We discuss our new results with revisiting the magnetic [χ(T)], transport [ρ(T)], and thermodynamic [Cp(T)] properties in order to better understand the phenomenon of thermal and electron transport in this compound. The field dependence of the magnetoresistivity data is also given. The temperature dependence of thermoelectric power S(T) was found to exhibit a similar behaviour as expected for Yb-based compounds with divalent or nearly divalent Yb ions. In addition, the values of total thermal conductivity as a function of temperature κ(T) of YbNiAl4 are fairly low compared to those of pure metals which may be linked to the fact that the conduction band is perturbed by strong hybridization. A deeper analysis of the specific heat revealed the low-T anomaly of the ratio Cp(T)/T3, most likely associated with the localized low-frequency oscillators in this alloy. In addition, the Kadowaki-Woods ratio and the Wilson ratio are discussed with respect to the electronic correlations in YbNiAl4.

Optical properties of ytterbium‐doped yttrium oxide ceramics

Ytterbium‐doped yttrium oxide (Yb:Y2O3) transparent ceramics with different sintering additives (Lu2O3, Sc2O3, CeO2, ZrO2, or HfO2) were fabricated using nanopowders produced by laser ablation. Transmission and photoluminescence spectra of the obtained ceramics were investigated at room temperature. Highest in‐line transmittance was over 80% at the wavelength of 1060 nm for 2 mm thick Yb:Y2O3 ceramics with zirconium and hafnium. Divalent Yb ions with the ground state electron configuration 4f136s were revealed. The absorption and emission bands caused by s↔s transitions of these ions were observed in the IR spectral range of Yb3+ ions. The superposition of both Yb3+ and Yb2+ emission bands leads to an effective broadening of the whole luminescence band.

Electronic structure and X-ray spectroscopic properties of YbNi2P2

X-ray absorption spectrum at the Yb L3 edge and X-ray emission spectra of Ni and P at the K and L2,3 edges have been studied experimentally and theoretically in the mixed valent compound YbNi2P2 with ThCr2Si2 type crystal structure. The electronic structure of YbNi2P2 is investigated using the fully relativistic Dirac linear muffin-tin orbital (LMTO) band-structure method. The effect of the spin–orbit (SO) interaction and Coulomb repulsion U on the electronic structure of YbNi2P2 is examined in the frame of the LSDA+SO+U method. The core-hole effect in the final states as well as the effect of the electric quadrupole E2 transitions have been investigated. A good agreement between the theory and the experiment was found. Both the trivalent and the divalent Yb ions in YbNi2P2 are reflected in the experimentally measured Yb L3 X-ray absorption spectrum simultaneously. We found that the best agreement between the experimental spectrum and sum of the theoretically calculated Yb2+ and Yb3+ spectra is achieved with 73% ytterbium ions in 2+ state and 27% ions in 3+ state.

The determination of dopant ion valence distributions in insulating crystals using XANES measurements

Ytterbium-doped wide-bandgap fluoride crystals CaF2, SrF2 and NaMgF3 have been measured using x-ray absorption near edge structure (XANES) on the L3 edge to determine the ratio of trivalent to divalent Yb ions present in the crystals. This study improves upon previous XANES measurements of dopant ion valency by taking into account the x-ray emission transition probabilities for the divalent and trivalent species instead of simply assuming that the relative concentrations may be determined by the ratio of the x-ray excitation band areas. Trivalent to divalent ratios as high as 5 are inferred even at low total dopant ion concentrations of 0.05 mol% Yb.

Low lattice-thermal conductivity in a cage-structured compound YbCu9Sn4 with divalent Yb ions

Polycrystalline sample of YbCu9Sn4 has been prepared and the physical properties have been investigated. Magnetic susceptibility shows a weak diamagnetism, indicating the Yb ions are in the nonmagnetic Yb2+ state. Electrical resistivity shows a normal metallic behavior and Seebeck coefficient is as small as the order of 1μV/K. Specific heat reveals the prominent contribution of Einstein mode at low temperature with the Einstein temperature of 67K. Lattice thermal conductivity is found to be as small as 2.7W/Km below room temperature. These results demonstrate that the Yb ions inside the Cu–Sn cage exhibit rattling, which reduces the lattice thermal conductivity of YbCu9Sn4.

Crystal structure and physical properties of the novel stannide Yb3Pd2Sn2

The crystal structure and the physical properties at low temperatures of the novel stannide Yb3Pd2Sn2 have been studied. The compound crystallizes in a new structure type, space group Pbcm, with Yb occupying four different positions in the lattice. Measurements of DC susceptibility and 170Yb Mössbauer suggest a close to divalent Yb-ions behaviour, ruling out a scenario of heterogeneous mixed valence for the Yb-ions.

Electrical and magnetic properties of TmCoIn 5 and YbCoIn 5 single crystals

Electrical and magnetic properties of TmCoIn 5 and YbCoIn 5 single crystals were investigated by means of electrical resistivity and magnetization measurements in the temperature range from 300 to 0.5 K under the magnetic field up to 5 T. TmCoIn 5 is an antiferromagnetic metal with a Néel temperature T N=2.6 K. YbCoIn 5 shows non-magnetic behavior, reflecting of divalent Yb ion.

Growth of YbF3-doped CaF2 crystals and characterization of Yb3+/Yb2+ conversion

Abstract Calcium fluoride crystals doped with YbF 3 and PbF 2 -, NaF- and LiF-codoped were grown using the vertical Bridgman method. Transparent, high quality, with various high Yb 2+ contents in the as-grown crystals has been obtained using a special procedure. The optical absorption spectra reveal the characteristic ultraviolet (UV) absorption bands of the divalent Yb ions. Influence of the codoping with Pb 2+ , Li + and Na + ions on the absorption spectra and on the Yb 2+ ions content has been studied. High-intensity emission bands in the near-UV spectral region, not reported before, have been observed for excitation by 230 nm. A comparison of our results with those obtained by other authors is also given.

Magnetic properties in [formula omitted] (R=rare earth)

We succeeded in growing single crystals of RRhIn 5 (R: rare earth) and measured the magnetic susceptibility and magnetization. The lattice constants of RRhIn 5 with the tetragonal structure are well understood from a viewpoint of the lanthanide contraction, except YbRhIn 5 with the divalent Yb ion. Most of RRhIn 5 compounds order antiferromagnetically. NdRhIn 5 indicates two metamagnetic transitions at H m 1 = 7.2 and H m 2 = 9.6 T below T N for the magnetic field along the [0 0 1] direction. The saturation moment of 2.5 μ B / Nd is in good agreement with a staggered Nd moment determined by the neutron scattering experiment. The similar metamagnetic transitions were observed in TbRhIn 5 , DyRhIn 5 and HoRhIn 5 .

Electronic Structure of YbTX Compounds

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electronic structure of YbTX compounds

The electronic structure of ternary YbTX compounds (T=Au, Pd, Rh, Pt; X=Sn, Bi) was studied by X-ray photoemission spectroscopy (XPS). XPS valence bands were compared with calculations using the tight-binding linear muffin-tin orbital method. The results showed that the valence bands in these compounds were formed mainly by the 4f orbitals of ytterbium and the 4d (5d) orbitals of the transition elements. Analysis of the Yb 4f valence band and Yb 4d core level states clearly indicated the presence of divalent Yb ions in YbAuSn and YbAuBi, and trivalent ions in YbRhSn and YbPtSn. In turn, the Yb ions in YbPdBi exhibited a mixed valence character.

Magnetic and transport properties of YbRhIn and YbPdIn

Electrical resistivity, magnetization and specific heat have been measured on a single crystal of YbRhIn and polycrystals of LuRhIn and YbPdIn. It is confirmed that YbPdIn is a metal with a divalent Yb ion. For YbRhIn, the electrical resistivity increases with logarithmic temperature dependence with decreasing temperature and saturates at a constant value below 20 K, while that of the nonmagnetic reference LuRhIn shows typical metallic behavior. The magnetic susceptibility of YbRhIn indicates that the Yb ion is in the trivalent state. The irreversibility of the magnetization curves which is observed in the high pulsed magnetic field below 1.5 K suggests an increase of relaxation time in the magnetic system. The specific heat increases rapidly below 4 K with decreasing temperature down to 0.9 K and moves toward higher temperatures on application of a magnetic field. These facts suggest that some magnetic transition to either ferromagnetic or spin-glass state occurs at low temperature.

Ab initiotheory of valency in ytterbium compounds

The electronic structure of 26 Yb compounds is calculated with the ab initio self-interaction-corrected local-spin-density approximation. In this approach f electrons can be described as either localized or delocalized. Hence a divalent Yb ion is represented with a completely localized f14 shell, while a trivalent Yb ion is represented with a localized f13 shell with the remaining 14th f electron giving rise to a very narrow f resonance, which straddles the Fermi energy. The systems studied comprise the Yb monopnictides and monochalcogenides as well as a series of intermetallic compounds. Experimental equilibrium volumes are well reproduced. The results provide quantitative support to the experimental classification of Yb compounds in terms of effective valencies.

Preparation and spectroscopy of Yb 2+-doped Y 3Al 5O 12, YAlO 3, and LiBaF 3

We report on the preparation and spectroscopic properties of Yb 2+ in Y 3Al 5O 12, YAlO 3 and LiBaF 3 with respect to the realization of a tunable solid-state laser based on a 5d–4f transition of Yb 2+. We observe broad emission bands in the region of 470 nm (LiBaF 3) and 580 nm (YAlO 3) due to the 4f–5d transition correlated with the divalent Yb ion. Exciton-like states, formed by a delocalized electron in the conduction band and an Yb 3+ ion, are also involved in the excitation and emission mechanism.

Electrical resistivity measurements on some R 5Si 3 phases: R = Gd, Tb, Yb, Lu and Y

The electrical resistivity of the R 5 Si 3 phases with R = Gd, Tb, Yb, Lu, Y has been measured in the 10–800 K temperature range. The compounds of Gd and Tb exhibit one transformation point, which can be ascribed to magnetic transitions. The temperature dependence of the resistivity of Y 5 Si 3 and Lu 5 Si 3 has been described by a combination of the phonon contribution and an interband scattering term. For Yb 5 Si 3, the different behaviour in the electrical resistivity, the low value of the magnetic moment as well as the anomalous values of the elementary cell constants can be explained assuming a mixed valent state of Yb: a divalent Yb ion in one site set and a trivalent Yb ion in the other site.