More Like this

1. Anisotropic magnetic and transport properties of orthorhombic o-Pr 2 Co 3 Ge 5

   https://doi.org/10.1088/2515-7639/ac9ad9  

   Kyrk, Trent M. ; Kennedy, Ellis R. ; Galeano-Cabral, Jorge ; Wei, Kaya ; McCandless, Gregory T. ; Scott, Mary C. ; Baumbach, Ryan E. ; Chan, Julia Y. ( October 2022 , Journal of Physics: Materials)

   The crystal structure, electron energy-loss spectroscopy (EELS), heat capacity, and anisotropic magnetic and resistivity measurements are reported for Sn flux grown single crystals of orthorhombic Pr₂Co₃Ge₅(U₂Co₃Si₅-type,Ibam). Our findings show thato-Pr₂Co₃Ge₅hosts nearly trivalent Pr ions, as evidenced by EELS and fits to temperature dependent magnetic susceptibility measurements. Complex magnetic ordering with a partially spin-polarized state emerges nearT_sp= 32 K, with a spin reconfiguration transition nearT_M= 15 K. Heat capacity measurements show that the phase transitions appear as broad peaks in the vicinity ofT_spandT_M. The magnetic entropy further reveals that crystal electric field splitting lifts the Hund’s rule degeneracy at low temperatures. Taken together, these measurements show that Pr₂Co₃Ge₅is an environment for complexfstate magnetism with potential strongly correlated electron states.

    

   more » « less
2. Exploring the optical properties of La 2 Hf 2 O 7 :Pr 3+ nanoparticles under UV and X-ray excitation for potential lighting and scintillating applications

   https://doi.org/10.1039/c8nj00895g  

   Zuniga, Jose P. ; Gupta, Santosh K. ; Pokhrel, Madhab ; Mao, Yuanbing ( January 2018 , New Journal of Chemistry)

   New optical materials with efficient luminescence and scintillation properties have drawn a great deal of attention due to the demand for optoelectronic devices and medical theranostics. Their nanomaterials are expected to reduce the cost while incrementing the efficiency for potential lighting and scintillator applications. In this study, we have developed praseodymium-doped lanthanum hafnate (La 2 Hf 2 O 7 :Pr 3+ ) pyrochlore nanoparticles (NPs) using a combined co-precipitation and relatively low-temperature molten salt synthesis procedure. XRD and Raman investigations confirmed ordered pyrochlore phase for the as-synthesized undoped and Pr 3+ -doped La 2 Hf 2 O 7 NPs. The emission profile displayed the involvement of both the 3 P 0 and 1 D 2 states in the photoluminescence process, however, the intensity of the emission from the 1 D 2 states was found to be higher than that from the 3 P 0 states. This can have a huge implication on the design of novel red phosphors for possible application in solid-state lighting. As a function of the Pr 3+ concentration, we found that the 0.1%Pr 3+ doped La 2 Hf 2 O 7 NPs possessed the strongest emission intensity with a quantum yield of 20.54 ± 0.1%. The concentration quenching, in this case, is mainly induced by the cross-relaxation process 3 P 0 + 3 H 4 → 1 D 2 + 3 H 6 . Emission kinetics studies showed that the fast decaying species arise because of the Pr 3+ ions occupying the Hf 4+ sites, whereas the slow decaying species can be attributed to the Pr 3+ ions occupying the La 3+ sites in the pyrochlore structure of La 2 Hf 2 O 7 . X-ray excited luminescence (XEL) showed a strong red-light emission, which showed that the material is a promising scintillator for radiation detection. In addition, the photon counts were found to be much higher when the NPs are exposed to X-rays when compared to ultraviolet light. Altogether, these La 2 Hf 2 O 7 :Pr 3+ NPs have great potential as a good down-conversion phosphor as well as scintillator material. 

   more » « less
3. Room-temperature valence transition in a strain-tuned perovskite oxide

   https://doi.org/10.1038/s41467-022-35024-8  

   Chaturvedi, Vipul ; Ghosh, Supriya ; Gautreau, Dominique ; Postiglione, William M. ; Dewey, John E. ; Quarterman, Patrick ; Balakrishnan, Purnima P. ; Kirby, Brian J. ; Zhou, Hua ; Cheng, Huikai ; et al ( December 2022 , Nature Communications)

   Cobalt oxides have long been understood to display intriguing phenomena known as spin-state crossovers, where the cobalt ion spin changes vs. temperature, pressure, etc. A very different situation was recently uncovered in praseodymium-containing cobalt oxides, where a first-order coupled spin-state/structural/metal-insulator transition occurs, driven by a remarkable praseodymium valence transition. Such valence transitions, particularly when triggering spin-state and metal-insulator transitions, offer highly appealing functionality, but have thus far been confined to cryogenic temperatures in bulk materials (e.g., 90 K in Pr_1-xCa_xCoO₃). Here, we show that in thin films of the complex perovskite (Pr_1-yY_y)_1-xCa_xCoO_3-δ, heteroepitaxial strain tuning enables stabilization of valence-driven spin-state/structural/metal-insulator transitions to at least 291 K, i.e., around room temperature. The technological implications of this result are accompanied by fundamental prospects, as complete strain control of the electronic ground state is demonstrated, from ferromagnetic metal under tension to nonmagnetic insulator under compression, thereby exposing a potential novel quantum critical point.

    

   more » « less
4. Spectroscopic and electrochemical characterization of a Pr 4+ imidophosphorane complex and the redox chemistry of Nd 3+ and Dy 3+ complexes

   https://doi.org/10.1039/D2DT00758D  

   Rice, Natalie T. ; Popov, Ivan A. ; Carlson, Rebecca K. ; Greer, Samuel M. ; Boggiano, Andrew C. ; Stein, Benjamin W. ; Bacsa, John ; Batista, Enrique R. ; Yang, Ping ; La Pierre, Henry S. ( May 2022 , Dalton Transactions)

   The molecular tetravalent oxidation state for praseodymium is observed in solution via oxidation of the anionic trivalent precursor [K][Pr 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (1-Pr(NP*)) with AgI at −35 °C. The Pr 4+ complex is characterized in solution via cyclic voltammetry, UV-vis-NIR electronic absorption spectroscopy, and EPR spectroscopy. Electrochemical analyses of [K][Ln 3+ (NP(1,2-bis- t Bu-diamidoethane)(NEt 2 )) 4 ] (Ln = Nd and Dy) by cyclic voltammetry are reported and, in conjunction with theoretical modeling of electronic structure and oxidation potential, are indicative of principal ligand oxidations in contrast to the metal-centered oxidation observed for 1-Pr(NP*). The identification of a tetravalent praseodymium complex in in situ UV-vis and EPR experiments is further validated by theoretical modeling of the redox chemistry and the UV-vis spectrum. The latter study was performed by extended multistate pair-density functional theory (XMS-PDFT) and implicates a multiconfigurational ground state for the tetravalent praseodymium complex. 

   more » « less
5. Comparing Pr 3+ and Nd 3+ for deactivating the Er 3+ :  4 I 13/2 level in lanthanum titanate glass

   https://doi.org/10.1364/OME.517790  

   Topper, Brian ; Neumann, Alexander ; Wilke, Stephen K. ; Youngman, Randall E. ; Alrubkhi, Abdulrahman ; Weber, Richard ( April 2024 , Optical Materials Express)

   Erbium lanthanum titanate glasses were prepared by levitation melting for the spectroscopic study of ways to promote the mid-infrared fluorescence. Two series of heavily erbium doped glasses (15 wt%) were prepared with the addition of either Pr³⁺or Nd³⁺in amounts relative to Er³⁺of 0.05, 0.1, and 0.2. Both ions quench the lower Er³⁺laser level with the Pr³⁺doing so more rapidly. Although high co-dopant concentrations result in higher energy transfer, as clearly evidenced in upconversion and downconversion fluorescence measurements, the mid-infrared lifetime also suffers a reduction and, therefore, a balance must be struck in the co-dopant concentration. Lifetime and spectral measurements indicate that, at a fixed relative co-dopant amount, Pr³⁺is more effective than Nd³⁺at removing the bottleneck of the Er^3+ 4I_13/2level. Moreover, consideration of the lifetimes alongside the absorption data of the individual ions indicates that despite the large absorption cross-section of Nd³⁺at 808 nm, the concentration needed to yield more absorbed power than utilizing direct 976 nm excitation of Er³⁺results in unfavorable lifetimes of the mid-infrared transition. In the end, Pr³⁺prevails as the superior co-dopant in terms of the effects on fluorescence lifetimes as well as potential laser system design considerations. In a unique self-doping approach, a reducing melt atmosphere of Ar instead of O₂creates a small fraction of Ti³⁺. In 5Er₂O₃-12La₂O₃-83TiO₂glass, the presence of Ti³⁺quenches the⁴I_13/2emission about 2.6 times more than the⁴I_11/2when lifetimes are compared to an O₂melt environment. As an additional means of increasing the mid-infrared emission, the effect of temperature on the mid- and near- infrared lifetimes of a lightly doped lanthanum titanate composition is investigated between 77-300 K. The mid-infrared lifetime increases by ∼30% while the near-infrared lifetime increases by ∼10%, which suggests in addition to co-doping, active cooling of the gain media will further enhance performance.

    

   more » « less