Excited Multiplets Research Articles

Dual-mode downconversion luminescence with broad near-ultraviolet and blue light excitation in Tm3+/Yb3+ codoped oxy-fluoride glasses for c-Si solar cells

In this work, we demonstrated an efficient dual-mode solar spectral converter Tm3+/Yb3+ co-doped oxy-fluoride glasses synthesized using high temperature melt-quenching method. The transmittance, photoluminescence emission (PL) and photoluminescence excitation (PLE) spectra and decay dynamics have been systematically investigated. The experimental results revealed that two distinct solar spectral converting processes, quantum cutting (QC) and down-shifting (DS) were achieved through the sensitization of Tm3+ excited multiplets and a broad band attributing to Yb3+-O2− charge transfer state (CTS), respectively. The prepared materials could convert the UV (250–370 nm) and blue (450–490 nm) photons into broad NIR emission (900–1100 nm), which coincides well with the most efficient spectral response of Si-based solar cells. The resultant Tm3+/Yb3+ co-doped oxy-fluoride glasses with dual-mode solar spectral modification indicate its potential application in improving the energy conversion efficiency of Si-based solar cells.

Magnetic susceptibilities, Raman spectroscopy and crystal field analysis of Pr3+ in monoclinic single crystals of PrPO4

Single crystals of praseodymium phosphate (PrPO4) are grown by flux method from Pb2P2O7 flux with PbF2 as an additive. The magnetic anisotropy of PrPO4 with different modes of suspensions (b-axis vertical, c-axis vertical and (100) plane horizontal) are measured in the temperature range of 300–80 K. The principal magnetic susceptibilities, χ1 and χ3 are measured from room temperature down to 14 K. The other principal magnetic susceptibility, χ2 is obtained from the value of anisotropy measured with b-axis vertical mode of suspension. The observed magnetic data of PrPO4 has been analyzed using one electron crystal field (CF) theory with rare earth site symmetry as C2v. No ordering effect has been noticed in the observed magnetic data within the temperature range of our study, which indicates that the inter-ionic interaction is of dipolar type. To substantiate the crystal field analysis, the Raman spectra of the single crystal in the wave number range of 0–1800 cm−1 has also been recorded. All the observed data like, magnetic susceptibilities including anisotropies, Stark energies extracted from Raman spectra etc. are considered in the CF analysis. Interestingly, the calculated values of CF electronic Stark energies in all the excited multiplets are in agreement with those extracted from the Raman data. Magnetic data are also successfully fitted by the CF analysis. The CF analysis provides the electronic specific heat capacity which gives Schottky anomalies at ∼48.5 K.

Down- and Upconversion Phenomena in Gd3(Al,Ga)5O12 Crystals Doped with Pr3+ and Yb3+ Ions

Single crystals of Gd3Al2.5Ga2.5O12, single-doped with Pr3+ ions and double-doped with Pr3+ and Yb3+ ions, were fabricated by the Czochralski technique. Transition intensities and relaxation dynamics of Pr3+ ions were determined employing the Judd–Ofelt treatment. Crystal field splitting of excited multiplets of incorporated luminescent ions were determined on the basis of optical spectra recorded at liquid helium temperature. The Pr3+ → Yb3+ energy-transfer phenomena were determined analyzing the effect of Yb3+ concentration on luminescence spectra and decay curves of Pr3+ ions. It was concluded that the observed downconversion phenomenon involves a quantum-cutting mechanism consisting of a two-step energy transfer from Pr3+ to Yb3+. We observed a phenomenon of nonresonant conversion of femtosecond pulses of infrared light into visible Pr3+ emission that was weakly affected by the wavelength of incident light at least in the 1100–1600 nm region. It was concluded that excitation mechanisms consist of multiphoton absorption of incident infrared radiation involving interconfigurational 4f2–4f15d transitions of Pr3+ and/or indirect excitation of Pr3+ ions by energy transfer from electrons created in the conduction band of the host.

Interplay of rare-earth and transition-metal subsystems inCu3Yb(SeO3)2O2Cl

We present the synthesis and the experimental and theoretical study of the new member of the francisite family, $\mathrm{C}{\mathrm{u}}_{3}\mathrm{Yb}{(\mathrm{Se}{\mathrm{O}}_{3})}_{2}{\mathrm{O}}_{2}\mathrm{Cl}$. The compound reaches an antiferromagnetic order at ${T}_{\mathrm{N}}=36.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and experiences first-order spin-reorientation transition to weakly ferromagnetic phase at ${T}_{\mathrm{R}}=8.7\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ evidenced in specific heat ${C}_{\mathrm{p}}$ and magnetic susceptibility \ensuremath{\chi} measurements. Distinctly different magnetization loops in $T<{T}_{\mathrm{R}}$ and ${T}_{\mathrm{R}}<T<{T}_{\mathrm{N}}$ temperature ranges reflect the interplay of rare-earth and transition-metal subsystems. At low temperatures, the saturation magnetization ${M}_{\mathrm{s}}\ensuremath{\sim}5.2\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ is reached in pulsed magnetic-field measurements. The electron spin resonance data reveal the complicated character of the absorption line attributed to response from both copper and ytterbium ions. Critical broadening of the linewidth at the phase transitions points to quasi-two-dimensional character of the magnetic correlations. The spectroscopy of $\mathrm{Y}{\mathrm{b}}^{3+}$ ions evidences splitting of the lowest-energy Kramers doublet of ${}^{2}{F}_{5/2}$ excited multiplet at ${T}_{\mathrm{R}}<T<{T}_{\mathrm{N}}$ while the ground Kramers doublet splits only at $T<{T}_{\mathrm{R}}$. We describe the magnetic properties both above and below the spin-reorientation transition in the framework of a unified approach based on the mean-field approximation and crystal-field calculations.

Crystal structure and magnetic properties of Ba2R2/3TeO6 (R = Y, La, Pr, Nd, Sm–Lu) double perovskites

A new series of cubic double perovskites BaTeO6 (R = Y, La, Pr, Nd, Sm–Lu) was synthesized via solid state reaction. The and ions are ordered on alternating octahedral sites, with the rare earth sites 2/3 occupied to balance the charge. The lattice parameters decrease monotonically from for Ba2TeO6 to for Ba2TeO6. The lattice parameter for R = Y is close to that of Ho. Analysis of the resulting bond lengths indicates a structural relaxation around the R ion site. Ba2TeO6, Ba2TeO6 and Ba2TeO6 show primarily temperature-independent magnetic susceptibility due to the lack of a local rare earth moment. For Ba2TeO6 and Ba2TeO6, the susceptibilities are influenced by Van Vleck-like contributions from excited state multiplets. For the remaining members, the Curie–Weiss law is followed with low-temperature deviations that can be associated with various degrees of crystalline electric field splitting. No magnetic ordering was observed down to 1.8 K in any of the compounds.

Intensities and spectral features of the – potential laser transition of Er3+ centers in CaF2–CeF3 disordered crystal**Project supported by Shanghai Engineering Research Center for Sapphire Crystals, China (Grant No. 14DZ2252500), the Fund of Key Laboratory of Optoelectronic Materials Chemistry and Physics Chinese Academy of Sciences (Grant No. 2008DP17301), the Fundamental Research Funds for the Central Universities of China, the National

A CaF2–CeF3 disordered crystal containing 1.06% of Er3+ ions was grown by the temperature gradient technique. Optical absorption and emission spectra recorded at room temperature and at 10 K, luminescence decay curve recorded at room temperature, and extended x-ray-absorption fine structure spectra were analyzed with an intention to assess the laser potential related to the transition of Er3+. In addition, the thermal diffusivity of the crystal was measured at room temperature. The analysis of room-temperature spectra revealed that the emission is long-lived with a radiative lifetime value of 5.5 ms, peak emission cross section of , and large spectral width pointing at the tunability of the emission wavelength in the region stretching from approximately 1480 nm to 1630 nm. The energies of the crystal field components for the ground and excited multiplets determined from low-temperature absorption and emission spectra made it possible to predict successfully the spectral position and shape of the room-temperature emission band. Based on the correlation of the optical spectra and dynamics of the luminescence decay, it was concluded that in contrast to Yb3+ ions in heavily doped CaF2 erbium ions in the CaF2–CeF3 crystal reside in numerous sites with dissimilar relaxation rates.

Natural optical activity of f-f transitions in ErAl3(BO3)4 single crystal

Absorption and natural circular dichroism (NCD) spectra of ErAl3(BO3)4 single crystal were measured at 90K in the range of 10,000–28,200cm−1. The spectra were decomposed on the Lorentz shape components and the natural optical activities (NOA) of f-f transitions between Stark components of the ground and excited multiplets were found. The NCD spectra permitted us to find out existence of two non equivalent positions of Er3+ ion in one of its excited states, which are due to the local decrease of the crystal symmetry in this state. Very large NOA of a vibronic line was revealed. This phenomenon was accounted for basing on the new quantum mechanical formula for the NOA of electron transitions. The principle difference of the NOA properties of electric dipole allowed and parity forbidden transitions is discussed.

Muon spin relaxation and inelastic neutron scattering investigations of the all-in/all-out antiferromagnetNd2Hf2O7

${\mathrm{Nd}}_{2}{\mathrm{Hf}}_{2}{\mathrm{O}}_{7}$, belonging to the family of geometrically frustrated cubic rare-earth pyrochlore oxides, was recently identified to order antiferromagnetically below ${T}_{\mathrm{N}}\ensuremath{\approx}0.55$ K with an all-in/all-out arrangement of ${\mathrm{Nd}}^{3+}$ moments, however, with a much reduced ordered state moment. Herein, we investigate the spin dynamics and crystal-field states of ${\mathrm{Nd}}_{2}{\mathrm{Hf}}_{2}{\mathrm{O}}_{7}$ using muon spin relaxation $(\ensuremath{\mu}\mathrm{SR})$ and inelastic neutron scattering (INS) measurements. Our $\ensuremath{\mu}\mathrm{SR}$ study confirms the long-range magnetic ordering and shows evidence for coexisting persistent dynamic spin fluctuations deep inside the ordered state down to 42 mK. The INS data show the crystal electric field (CEF) excitations due to the transitions both within the ground-state multiplet and to the first excited state multiplet. The INS data are analyzed by a model based on CEF and crystal-field states are determined. Strong Ising-type anisotropy is inferred from the ground-state wave function. The CEF parameters indicate the CEF-split Kramers doublet ground state of ${\mathrm{Nd}}^{3+}$ to be consistent with the dipolar-octupolar character.

Optical spectra and emission characteristics of terbium-doped potassium–lead double chloride crystals (KPb2Cl5:Tb3+)

Optical transitions in KPb2Cl5:Tb3+ crystals are studied experimentally and theoretically. The absorption cross-section spectra are plotted and the oscillator strengths of transitions from the ground terbium state to excited multiplets are determined. Intensity parameters Ωt for KPC:Tb3+ are determined by the Judd–Ofelt method to be Ω2 = 2.70 × 10–20 cm2, Ω4 = 7.0 × 10–20 cm2, and Ω6 = 0.72 × 10–20 cm2. These values were used to calculate such characteristics of spontaneous radiative transitions as oscillator strengths, probabilities of radiative transitions, and radiative lifetimes. The emission spectra of KPb2Cl5:Tb3+ crystals upon UV excitation and the decay kinetics of luminescence from the excited 5 D 3 and 5 D 4 levels are studied experimentally, the lifetimes of these levels are determined, and the dependences of the rates of nonradiative relaxation from the excited 7 F j (j = 0–5), 5 D 4, and 5 D 3 levels to lower-lying terbium levels are calculated. It is shown that the population of the 5 D 4 level in KPC:Tb3+ crystals occurs according to a cascade scheme, which leads to quenching of the 5 D 3 level. The calculated data agree well with the known experimental rates of multiphonon nonradiative transitions for Dy:KPC, Nd:KPC, Er:KPC, Tb:KPB, and Nd:KPB crystals. It is shown that transitions in the near-IR (3–6 μm) region in double halide crystals (MPb2Hal5) are almost unquenched and the rates of nonradiative relaxation of excited levels spaced by energy gaps ΔE ji > 1000 cm–1 are W ji NR < 103s–1. This circumstance suggests that it is possible to obtain stimulated emission in KPb2Cl5:RE3+ crystals in the IR spectral region up to 6 μm.

A New Approach for Obtaining the Non-Strange Baryons Spectrum in a Phenomenological Interaction Potential

In our work, we present the nonrelativistic quark model and a new mass formula for study the non-strange baryons octet and decuplet masses. Our model contains a dominant SU(6)-invariant part accounting for the average multiplet energies, and a perturbative SU(6)-violating interaction for the splitting within the multiplets, a structure which is inspired by early Lattice QCD calculations. For our purpose we introduced a spin independent description for SU(6) invariant part of the spectrum, we presented the analytical solution of three particle Schrodinger equation under the suitable phenomenological interaction potential by using the anzast method, through which the average energy values of the nonstrange resonances are reproduced. To describe the hyperfine structure of the baryon and splittings within the SU(6)-multiplets, we used the generalized Gursey Radicati mass formula. A comparison between our calculations and the experimental data shows that the spectrum of the Roper resonances, the ground states and the excited multiplets up to three GeV are in general well reproduced and comparable with the experimental spectrum. Also one can conclude that; the interaction between the quark constituents of baryon resonances could be described adequately by using the combination of Killingbeck and isotonic oscillator potentials form.

Crystal electric field effects and thermal expansion of rare-earth hexaborides

Abstract Anomalies in the magnetic contribution to the thermal expansion coefficients ∆β(T) of the CeB 6 , PrB 6 , and NdB 6 hexaborides in the range of 5–300 K were found by comparison with diamagnetic LaB 6 . The characteristic of the anomalies was the same in all the studied borides: a distinct peak at low temperatures, followed by a broad maximum at higher temperatures (50–100 K), then a decrease and transition to the region of negative values as the temperature increases further. The features of ∆β(T) are explained by the effects of the magnetic order (sharp low temperature peaks) and the crystal electric field (CEF). The β CEF (T) dependencies were calculated using Raman and neutron scattering data on the splitting of the rare-earth (RE) ions R 3+ f-level by the CEF. A satisfactory consistency between the values of β CEF (T) and ∆β(T) was obtained for the studied hexaborides. Additionally, we determined the values of the Gruneisen parameter γ i that correspond to the transition between the ground and excited multiplets of R 3+ ions f-level splitting.

Optical and magneto-optical spectra and electron structure of ErAl3(BO3)4 single crystal

Linearly polarized absorption spectra and magnetic circular dichroism (MCD) spectra of ErAl3(BO3)4 single crystal were measured in the range of 10000–27000 cm−1 at 90 K. The Stark components of the ground and excited multiplets of Er3+ ion were identified in terms of the irreducible representations, basing on the linearly polarized absorption spectra. MCD spectra permitted us to measure the Zeeman splitting of some transitions and so to determine changes of the Landé factors along the C3 axis during these transitions. Additionally, the MCD spectra permitted us to identify some states in the |J,±MJ〉 function approximation. In particular, it was shown that the ground state of the Er3+ ion in this approximation has MJ = ± 13/2 that corresponds to magnetic moment m = ±7.8 μB. Very intensive f-f vibronic transitions, corresponding to electron transitions from the upper components of the ground multiplet, were revealed. Energies of the local vibrations in a number of the excited states were found.

Optical spectroscopy and decoherence studies ofYb3+:YAG at 968 nm

The $^{2}F_{7/2}\ensuremath{\leftrightarrow}^{2}F_{5/2}$ optical transitions of $\mathrm{Y}{\mathrm{b}}^{3+}$ doped into ${\mathrm{Y}}_{3}\mathrm{A}{\mathrm{l}}_{5}{\mathrm{O}}_{12}$ (YAG) were studied for potential quantum information and photonic signal processing applications. Absorption and fluorescence spectroscopy located the energy levels of the ground $^{2}F_{7/2}$ and excited $^{2}F_{5/2}$ manifolds, allowing inconsistencies between previous assignments of crystal field splittings in the literature to be resolved. These measurements reveal an unusually large splitting between the first and second levels in both the ground and excited multiplets, potentially providing for reduced sensitivity to thermally induced decoherence and spin-lattice relaxation. Spectral hole burning through two-level saturation was observed, determining the excited state lifetime to be 860 \ensuremath{\mu}s and resolving ambiguities in previous fluorescence measurements that were caused by the large radiation trapping effects in this material. Optical decoherence measurements using two-pulse photon echoes gave a homogeneous linewidth of 18 kHz for an applied magnetic field of 1 T, narrowing to 5 kHz at 2.5 T. The observed decoherence was described by spectral diffusion attributed to $\mathrm{Y}{\mathrm{b}}^{3+}\mathrm{\ensuremath{-}}\mathrm{Y}{\mathrm{b}}^{3+}$ magnetic dipole interactions. Laser absorption determined an inhomogeneous linewidth of 3.6 GHz for this transition in this 0.05%-doped crystal, which is narrower than for any other rare-earth-ion transition previously studied in the YAG host. The temperature dependence of the transition energy and linewidth of the lowest $^{2}F_{7/2}$ to lowest $^{2}F_{5/2}$ transition centered at 968.571 nm measured from 4 K to 300 K was well described by phonon scattering at higher temperatures, with an additional anomalous linear temperature-dependent broadening at temperatures below 80 K. Two magnetically inequivalent subgroups of $\mathrm{Y}{\mathrm{b}}^{3+}$ ions were identified when a magnetic field was applied along the $\ensuremath{\langle}111\ensuremath{\rangle}$ axis, as expected for the ${D}_{2}$ sites in the cubic symmetry crystal, with ground and excited state effective $g$-values of ${g}_{\mathrm{g}}=3.40$ (3.34) and ${g}_{\mathrm{e}}=1.04$ (2.01), respectively. Together with the convenient diode laser wavelength of this transition, our study suggests that $\mathrm{Y}{\mathrm{b}}^{3+}$:YAG is a promising material system for spectral hole burning and quantum information applications.

Excited state relaxation dynamics and up-conversion phenomena in Gd3(Al,Ga)5O12 single crystals co-doped with erbium and ytterbium

Single crystals of Gd3(Al,Ga)5O12 (GAGG) doped with Er3+ or Yb3+ ions and co-doped with Er3+ and Yb3+ ions were grown successfully by the Czochralski technique. Their optical properties were investigated in detail. Rates of radiative transitions, branching ratio values and radiative lifetimes for excited multiplets of incorporated Er3+ were determined based on the Judd–Ofelt treatment of optical absorption spectra recorded at room temperature. Obtained parameters Ωt (t=2, 4, and 6) are 1.47×10−20cm2, 1.38×10−20cm2, and 1.19×10−20cm2 respectively. Low energy crystal levels of Er3+ in GAGG were determined employing absorption and luminescence spectra recorded at 5K. Consequently, the energy diagram constructed was used to substantial discussion of obtained experimental data. Up-conversion of infrared radiation at 980nm into visible emission in crystals co-doped with erbium and ytterbium was observed and discussed. It was concluded that gathered spectroscopic data point at the potential of the GAGG:Yb3+, Er3+ system for application as a laser active material operating around 1500nm within the 4I13/2→4I15/2 transition of Er3+.

Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths

In the context of observations of the rest-frame ultraviolet and optical emission from distant galaxies, we explore the emission-line properties of photoionization models of active and inactive galaxies. Our aim is to identify new line-ratio diagnostics to discriminate between gas photoionization by active galactic nuclei (AGN) and star formation. We use a standard photoionization code to compute the emission from AGN narrow-line regions and compare this with calculations of the nebular emission from star-forming galaxies achieved using the same code. We confirm the appropriateness of widely used optical spectral diagnostics of nuclear activity versus star formation and explore new diagnostics at ultraviolet wavelengths. We find that combinations of a collisionally excited metal line or line multiplet, such as CIV 1548,1551, OIII]1661,1666, NIII]1750, [SiIII]1883+[SiIII]1892 and [CIII]1907+CIII]1909, with the HeII 1640 recombination line are individually good discriminants of the nature of the ionizing source. Diagrams involving at least 3 of these lines allow an even more stringent distinction between active and inactive galaxies, as well as valuable constraints on interstellar gas parameters and the shape of the ionizing radiation. Several line ratios involving Ne-based emission lines, such as [NeIV]2424, [NeIII]3343 and [NeV]3426, are also good diagnostics of nuclear activity. Our results provide a comprehensive framework to identify the sources of photoionization and physical conditions of the ionized gas from the ultraviolet and optical nebular emission from galaxies. This will be particularly useful to interpret observations of high-redshift galaxies with future facilities, such as the James Webb Space Telescope and extremely large ground-based telescopes.

A New Method for Obtaining the Baryons Mass under the Killingbeck Plus Isotonic Oscillator Potentials

The spectrum of ground state and excited baryons (N, Δ, Λ, Σ,Ξ, and Ω particles) has been investigated by using nonrelativistic quantum mechanics under the Killingbeck plus isotonic oscillator potentials. Using the Jacobi coordinates, anzast method, and generalized Gürsey Radicati (GR) mass formula the three-body-wave equation is solved to calculate the different states of the considered baryons. A comparison between our calculations and the available experimental data shows that the position of the Roper resonances of the nucleon, the ground states, and the excited multiplets up to three GeV are in general well reproduced. Also one can conclude that the interaction between the quark constituents of baryon resonances could be described adequately by using the combination of Killingbeck and isotonic oscillator potentials form.

Nucleon pairing in Sn isotopes

The systematics of excited states in Sn isotopes are discussed on basis of pairing interaction in nuclei. Nucleon paring leads to formation of excited states multiplets. The estimation of multiplet splitting based on experimental nuclear masses allows one to calculate the position of excited states with different seniority in δ -approximation. The wide systematics of the spectra of Sn isotopes gives a possibility to check the pairing interaction for different subshells and consider the multiplets of excited states in the neutron-rich isotopes far from stability.

Excited state relaxation dynamics and up-conversion phenomena in Gd3(Al,Ga)5O12 single crystals co-doped with holmium and ytterbium

Single crystals of Gd3(Al,Ga)5O12 single doped with Ho3+ or Yb3+ ions and co-doped with Ho3+ and Yb3+ ions were grown by the Czochralski technique and investigated employing methods of optical spectroscopy. Rates of radiative transitions, branching ratio values and radiative lifetimes for excited multiplets of incorporated Ho3+ ions were determined based on the Judd–Ofelt treatment of optical absorption spectra recorded at room temperature. Absorption spectra and luminescence spectra recorded at 5 K made it possible to determine crystal field splitting for several low energy multiplets of Ho3+ ions and for the 2F5/2 multiplet of Yb3+ ions. Lifetimes of luminescent levels of incorporated holmium and ytterbium ions and the Yb3+ − Ho3+ energy transfer efficiency were determined based on analysis of recorded luminescence decay curves. Up-conversion of infrared radiation at 980 nm into yellow emission in crystals co-doped with holmium and ytterbium was observed and discussed. It was found that the structural disorder of the Gd3(Al,Ga)5O12 host resulting from a disparity of ionic radii of Al and Ga ions induces an inhomogeneous broadening of spectral lines of incorporated luminescent ions but the crystal field splitting of their multiplets is similar to that encountered in ordered garnet hosts. Based on analysis of gathered spectroscopic data it was concluded that the Gd3(Al,Ga)5O12:Ho3+,Yb3+ crystals are promising materials for the design of laser-diode pumped infrared lasers operating near 2000 nm.

Study of spectroscopic properties of LiNbO3:Ho3+ crystal in 1880–2130 nm luminescence band

Theoretical study of spectroscopic properties of LiNbO3:Ho3+ crystal in the wavelength range of 1880–2130 nm was carried out, when the Stark structure of optical spectrum of the impurity ion was taken into account. Wave functions of Stark sublevels of the ground (5 I 8) and first excited (5 I 7) multiplets of the Ho3+ ion were defined, the line strengths induced by the indirect electric-dipole and magnetic-dipole intra-Stark transitions were calculated, and the main spectroscopic characteristics were determined on this basis.

Temperature dependent infrared absorption, crystal-field and intensity analysis of Ce3+ doped LiYF4

Infrared absorption has been used to determine the crystal-field levels of the 2F7/2 excited multiplet of trivalent cerium doped into scheelite structure LiYF4 single crystals. A crystal-field analysis well accounts for a total of six experimentally observed energy levels and the ground state g-values as previously determined by electron paramagnetic resonance, whilst intensity simulations confirm the experimentally assigned level symmetries. Temperature dependent spectral line broadening measurements highlight the importance of coupling to low frequency phonon modes of the YF8 tetrahedron.