3H4 Multiplet Research Articles

Systematical site investigation and temperature sensing in Pr3+-doped M3RE4O9 (M = Sr and Ba; RE = Sc, Y, Lu)

Site engineering is an important modulation strategy for adjusting the physicochemical properties of lanthanide luminescent ions and shows growing applications in the optoelectronic field. Herein, we explored the influence of changing M2+ (or RE3+) ions on the occupation preference of Pr3+ ions and related crystal-field splittings in Pr3+:M3RE4O9 (M = Sr and Ba; RE = Sc, Y, Lu). The obtained results indicated that Pr3+ ions possess two kinds of doping sites (M2+ (Site Ⅰ) and RE3+ (Site Ⅱ)) in Pr3+:Ba3Lu4O9 and Pr3+:Ba3Y4O9, while only occupying Site Ⅰ in Pr3+:Sr3Sc4O9 and Pr3+:Ba3Sc4O9. The variation of RE3+ ions has little impact on the crystal-field splitting of both the two types of Pr3+ luminescent sites, and by contrast, replacing M2+ ones influences the energy-level splitting of the 3H4 multiplet of Site Ⅰ obviously. Moreover, we found that the host emission of M3RE4O9 stemming from intrinsic oxygen defects shows an apparent thermally induced fluorescence quenching phenomenon. And based on the defect and Site Ⅱ emissions, both Pr3+:Ba3Lu4O9 and Pr3+:Ba3Y4O9 exhibit excellent temperature sensing performance, yielding maximum relative sensitivity (Sr) of 8.40%·K−1 (132K) and 7.89%·K−1 (129K), respectively. This work enriches the site engineering strategy in Pr3+-based optical functional materials and broadens the relevant application in temperature sensing.

Resonant inelastic x-ray spectroscopy on UO2 as a test case for actinide materials

Resonant inelastic x-ray spectroscopy at the uranium N4 absorption edge at 778 eV has been used to reveal the excitations in UO2 up to 1 eV. The earlier (1989) studies by neutron inelastic scattering of the crystal-field states within the 3H4 multiplet are confirmed. In addition, the first excited state of the 3F2 multiplet at ∼520 meV has been established, and there is a weak signal corresponding to the next excited state at ∼920 meV. This represents a successful application of soft x-ray spectroscopy to an actinide sample, and resolves an open question in UO2 that has been discussed for 50 years. The technique is described and important caveats are drawn about possible future applications.

Luminescence and energy transfer phenomena in Gd3 (Al,Ga)5O12 crystals single doped with thulium and co-doped with thulium and holmium

Single crystals of Gd3Al2.5Ga2.5O12 (GAGG) doped with Tm3+ ions and co-doped with Ho3+ and Tm3+ ions were grown by the Czochralski technique and investigated employing methods of optical spectroscopy. The room temperature absorption spectra of GAGG:Tm3+ were analysed in the framework of the Judd-Ofelt theory. Obtained phenomenological parameters Ω2 = 0.62 × 10−20cm2, Ω4 = 1.41 × 10−20cm2 and Ω6 = 0.80 × 10−20cm2 were used to determine rates of radiative transitions, branching ratio values and radiative lifetimes for excited multiples of incorporated Tm3+ ions. Effect of Tm3+ concentration on decay curves of Tm3+ luminescence was examined and spectroscopic parameters characterizing the donor-acceptor interaction responsible for self-quenching of the emission from the 1D2, 1G4 and 3H4 multiplets were evaluated applying the Inokuti-Hirayama model. The crystal field splitting of Tm3+ multiplets were determined based on low temperature absorption and emission spectra. The emission cross section for Tm3+: 3F4 → 3H6 luminescence was determined to be 0.31 × 10−20cm2 at maximum and corresponding experimental lifetime amounts to 4.3ms resulting in quantum efficiency η = 0.79. The calculated ratio of Tm-Ho to back-transfer processes (CTm-Ho/CHo-Tm) is 5.18.

Crystal-field study of magnetization and specific heat properties of frustrated pyrochlore Pr2Zr2O7

The experimental results of temperature dependent dc magnetic susceptibility, field dependent isothermal magnetization, magnetic specific heat and entropy of the pyrochlore Pr2Zr2O7 are simulated and analyzed using appropriate D3d crystal-field (CF) and anisotropic molecular field tensors at Pr-sites in the self-consistent mean-field approach involving four magnetically non-equivalent rare-earth spins on the tetrahedral unit of the pyrochlore structure. CF level pattern and wave-functions of the ground 3H4 multiplet of the Pr3+ ions are obtained considering intermediate coupling between different Russell-Saunders terms of the 4f2 electronic configurations of Pr-ion and J-mixing effects. CF analysis shows that the CF ground-state of the Pr3+ ion in Pr2Zr2O7 is a well-isolated doublet, with significant admixtures of terms coming from |MJ=±4〉 and |MJ=±1〉, and the Pr-spins are effectively Ising-like along the local <111> axes. Magnetic specific heat in zero-field is simulated by considering a temperature dependence of the exchange splitting of the ground doublet.

Analysis of the optical and magnetooptical spectra of non-Kramers Pr3+(4f2) in Y3Al5O12 complemented by crystal-field modelling

The spectra of the absorption, luminescence, magnetic circular dichroism (MCD) and magnetic circular polarization of luminescence (MCPL) in the praseodymium yttrium garnet aluminate Pr3+:YAG have been studied within the visible and near ultraviolet (UV) spectral range for temperature T=90K and 300K. Analysis of the spectral and the temperature dependences of the magnetooptical and optical spectra has made it possible to identify the optical 4f→4f transitions occurring between the Stark sublevels of the 1D2, 3P0 and 3H4 multiplets in Pr3+:YAG. It has been shown that for Pr3+:YAG in the MCD within the UV spectral range for the absorption bands due to allowed 4f→5d transitions, and also in the MCPL for the luminescence bands, respectively, due to forbidden 4f→4f transitions within the visible spectral range, a significant role is being played by the effect of quantum mechanical “mixing” of the states of the three lowest energy Stark singlets of the ground state 3H4 multiplet of the non-Kramers RE Pr3+ ion. A parameterized Hamiltonian defined to operate within the entire 4f2 ground electronic configuration of Pr3+ was used to model the experimental Stark levels, their irreducible representations (irreps) and wave functions. The crystal-field parameters were determined through use of a Monte-Carlo method in which nine independent crystal-field parameters, Bqk, were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 61 calculated to experimental Stark levels is 18cm−1.

Magnetic circular dichroism of Pr3+ ions in yttrium—Aluminium garnet crystals

The spectra of the absorption and magnetic circular dichroism in the praseodymium-yttrium garnet-aluminate Pr3+:YAG have been studied within the visible and near ultraviolet (UV) spectral range for temperature T = 90 K and 300 K. Analysis of the spectral and the temperature dependences of the magnetooptical and optical spectra has made it possible to identify the optical 4f → 4f transitions occurring between the Stark sublevels of the 1D2, 3P0, and 3H4 multiplets in Pr3+:YAG. It has been shown that in the MCD mechanism in Pr3+:YAG within the visible and UV spectral range for the absorption bands due to both forbidden 4f → 4f and allowed 4f → 5d transitions, a significant role is being played by the effect of quantum-mechanical “mixing” of the states of the three lowest-energy Stark singlets of the ground-state 3H4 multiplet of the non-Kramers RE Pr3+ ion.

The influence of photon excitation and proton irradiation on the luminescence properties of yttria stabilized zirconia doped with praseodymium ions

Lanthanide doped zirconia based materials are promising phosphors for lighting applications. Transparent yttria stabilized zirconia fibres, in situ doped with Pr3+ ions, were grown by the laser floating zone method. The single crystalline doped fibres were found to be homogeneous in composition and provide an intense red luminescence at room temperature. The stability of this luminescence due to transitions between the 1D2→3H4 multiplets of the Pr3+ ions (intra-4f2 configuration) was studied by photo- and iono-luminescence. The evolution of the red integrated photoluminescence intensity with temperature indicates that the overall luminescence decreases to ca. 40% of the initial intensity at 14K when heated to room temperature (RT). RT analysis of the iono-luminescence dependence on irradiation fluence reveals a decrease of the intensity (to slightly more than ∼60% of the initial intensity after 25min of proton irradiation exposure). Nevertheless the luminescence intensity saturates at non-zero values for higher irradiation fluences revealing good potential for the use of this material in radiation environments.

Polarized spectral properties and laser demonstration of Tm^3+-doped LiGd(MoO_4)_2 crystal

Trivalent thulium-doped LiGd(MoO4)2 single crystals have been grown by the Czochralski method. Room-temperature polarized absorption and fluorescence spectra of the crystals were analyzed. The fluorescence decay curves of the 1G4, 3H4, and 3F4 multiplets were measured, and the decay mechanisms of the 1G4 and 3H4 multiplets were discussed. Spectroscopic parameters related to the laser operation around 1.90&#x2009;&#x3bc;m via the 3F4&#x2192;3H6 transition have been evaluated. Finally, end-pumped by a Ti:sapphire laser at 795 nm, the room-temperature quasi-continuous wave 1.9&#x2009;&#x3bc;m laser emission was demonstrated with a slope efficiency of 28%.

Spectroscopic analysis and laser performance of Tm3+ : NaGd(MoO4)2 crystal

Detailed polarized spectral properties of Tm3+ : NaGd(MoO4)2 crystal have been investigated. The room temperature absorption and fluorescence spectra were recorded. The fluorescence decay mechanisms of the 1G4 and 3H4 multiplets in Tm3+ : NaGd(MoO4)2 crystal were discussed. Room temperature quasi-cw 1.9 µm laser emission from the Ti : sapphire laser pumped Tm3+ : NaGd(MoO4)2 crystal has been demonstrated. The maximum output power of 170 mW has been achieved with a slope efficiency of 25%.

The influence of the admixing of different multiplets on the spin magnetic moment and Faraday effect of rare earth ions in Garnets

The influence of the admixing of the excited multiplets of the ground configuration with the ground multiplet on the spin magnetic moment of the crystal- field- and exchange-interaction-split ground state, the Faraday rotation and the magneto-optic coefficient induced by the rare earth ions in rare-earth-substituted garnets Y3-xRxFe5O12 (R=Ce and Pr) has been calculated in this paper. It is found that, in the case of Ce3+ ions, the admixing of the 4f1 2F7/2 multiplet with the 2F5/2 multiplet makes the spin magnetic moment of the crystal-field- and exchange-interaction-split ground state increase by 140% and the Faraday rotation increase by 180% at 633 nm wavelength, and 150% at 1150 nm at 294 K. In the case of Pr3+ ions, the admixing of the 4f2 3H5 multiplet with the 3H4 multiplet makes the spin magnetic moment of the crystal-field- and exchange-interaction-split ground state increase by 34% and the Faraday rotation increase by 59% at 294 K. The admixing of different multiplets of the Ce3+ ions makes the ratio between the magneto-optic coefficients at 50 and 294 K increase by 7% at 633 nm wavelength and 15% at 1150 nm.

Investigation of Zeeman second-order effects in Pr3+:LaCl3using the fluorescence-line-narrowing technique

A technique involving the laser-induced narrowing of a fluorescence line is used to obtain high-resolution spectra of Pr3+:LaCl3. The second-order effects caused by Zeeman and nuclear interactions are systematically investigated in the 3H4E2 to or from 1D2A1 transition. A non-zero perpendicular Zeeman splitting of the ground level, proportional to the square of the magnetic field, is measured and interpreted as being caused by the perturbation by the four upper Stark levels belonging to the 3H4 multiplet. The variation of the number and of the relative intensities of the hyperfine lines is demonstrated to be closely related to the angle between the external magnetic field direction and the crystal axis. It is unambiguously attributed to an angular dependence, with regard to the magnetic field direction, of the hyperfine states of the excited level. The importance of the effect, caused by a very distant perturbing level, is shown to be a result of the quasidegeneracy of the mu =0 excited level.

Study of Crystal Field Splitting of Pr3+ in PrF3 by Inelastic Neutron Scattering

AbstractThe electrical crystal field (ECF) levels of the Pr3+ ion in PrF3 are studied by means of inelastic neutron scattering. Spectra are obtained at sample temperatures of 20, 80, and 300 K. From the theoretical analysis basing on an ECF parameter set for the isostructural Pr: LaF3 a complete scheme of the 3H4 multiplet of Pr3+ in PrF3 is proposed.

Calculation of the energy-level scheme of Pr 3+ in crystalline PrF 3 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 3H 4-multiplet of Pr 3+ in PrF 3 is determined. The results are shown to be in good agreement with the experiments.

Magnetic Properties of Uranium Compounds with NaCl Structure

A model is proposed to account for the properties of uranium compounds UX, where X is either an element of the VA group (N, P, As, Sb; UV compounds) or of the VIA group (S, Se, Te; Uvi). Uv compounds are antiferromagnetic, while Uvi are ferromagnetic. All have high transition temperatures (50–220) °K and low electrical resistivities. It is assumed that uranium is in the U4+ state (3H4 configuration) both in Uv and Uvi compounds and the 5f electrons are strongly localized. The X anions are triply ionized in Uv compounds, and doubly in Uvi. The surplus electrons form a conduction band. The U ions are treated by the methods of ``crystal field'' theory. The coupling between them is via the RKKY mechanism. The coupling constant is calculated to be in the range of 12 to 22 eV Å3. In the octahedral field present the 3H4 multiplet splits, so that the ground state is a singlet. The observed saturation moment depends on the relative strength of the crystal field and the exchange interaction. The crystal-field splittings derived are in the range 500–1200 cm−1. The model accounts for the observed types of magnetic ordering. The assumptions used are justified briefly.