Unravelling local spin polarization of Zhang-Rice singlet in lightly hole-doped cuprates using high-energy optical conductivity

Unrevealing local magnetic and electronic correlations in the vicinity of charge carriers is crucial in order to understand rich physical properties in correlated electron systems. Here, using high-energy optical conductivity (up to 35 eV) as a function of temperature and polarization, we observe a surprisingly strong spin polarization of the local spin singlet with enhanced ferromagnetic correlations between Cu spins near the doped holes in lightly hole-doped La$_{1.95}$Sr$_{0.05}$Cu$_{0.95}$Zn$_{0.05}$O$_{4}$. The changes of the local spin polarization manifest strongly in the temperature-dependent optical conductivity at ~7.2 eV, with an anomaly at the magnetic stripe phase (~25 K), accompanied by anomalous spectral-weight transfer in a broad energy range. Supported by theoretical calculations, we also assign high-energy optical transitions and their corresponding temperature dependence, particularly at ~2.5 ~8.7, ~9.7, ~11.3 and ~21.8 eV. Our result shows the importance of a strong mixture of spin singlet and triplet states in hole-doped cuprates and demonstrates a new strategy to probe local magnetic correlations using high- energy optical conductivity in correlated electron systems.Comment: 38 pages, 11 figure

Luminescence spectroscopy under synchrotron radiation: From SUPERLUMISUPERLUMI to FINESTLUMIFINESTLUMI

Luminescence spectroscopy under synchrotron radiation excitation is the unique tool for materials characterization. In the current work we are reporting recent activity in this research field implemented in the Finnish-Estonian beamline (FinEstBeAMS) which is installed at the 1.5 GeV storage ring of the MAX IV Laboratory at Lund, Sweden. It has been designed to cover an unusually wide energy range from ultraviolet (4.3 eV) to soft X-rays (1500 eV), which is perfectly suited for luminescence spectroscopy experiments. The past development and the present technical parameters of the luminescence experimental stations $FINESTLUMI$ of FinEstBeAMS beamline are described. The comparison of the experimental parameters of the $FINESTLUMI$ and $SUPERLUMI$ (this endstation was operated long period of time at DORIS III storage ring of DESY synchrotron at Hamburg, Germany) setups will be demonstrated. The experimental possibilities and limitations of the $FINESTLUMI$ as well as the recent luminescence experiments at FinEstBeAMS are briefly discussed

Revised crystal structure and luminescent properties of gadolinium oxyfluoride Gd4O3F6Gd_{4}O_{3}F_{6} doped with Eu3+Eu^{3+} ions

The structure of gadolinium oxyfluoride nanoparticles was revised. Extensive studies including X-ray diffraction and Rietveld refinement as well as Fourier transform infrared spectroscopy and Raman spectroscopy confirmed the monoclinic P12/c1 crystal structure of Gd4O3F6. Morphological analysis using transmission electron microscopy showed the nanocrystallinity of the materials prepared via the sol–gel Pechini's method. The luminescent properties of the prepared materials with different concentrations of Eu3+ ions were characterized by emission spectroscopy. The phosphors obtained were investigated in the vacuum ultraviolet range using synchrotron radiation. The Judd–Ofelt parameters (Ω2, Ω4) and emission efficiencies η were calculated and are discussed in detail

Intrinsic and extrinsic luminescence of nanosize transition alumina powders

Luminescence spectroscopy in the VUV-visible range under electron-beam excitation and synchrotron radiation was applied to investigate electronic properties of alumina nanopowders, which were prepared using the combustion synthesis method. By varying reaction and post treatment conditions we were able to prepare phase pure samples and powders with mixtures of α- and γ-phases mainly. In addition to the well-known 7.6 eV luminescence of STE of α-alumina, all samples possessed complex emission bands in UV range (3–5 eV) which originate from intrinsic excitonic emissions and extrinsic electronic excitations

Grain-size effect on Cr3+^{3+} and F-centres photoluminescence in nanophase MgAl2_2O4_4 ceramics

Photoluminescence (PL) spectroscopy of transparent MgAl$_2$O$_4$ spinel ceramics with grain size between 100 and 300 nm was studied at 7 K temperature in the near-IR-VUV range of spectrum with synchrotron radiation excitation. The PL spectra were composed of optical transitions from spatially different regions of the ceramics, which analysis evidenced grain size effect on the emission line-shapes and intensities. In particular, emission of impurity Cr$^{3+}$ ions, being structured in the crystalline bulk, became broad-band in the grain boundary regions, which was associated with respectively strong and weak local crystalline fields. It was observed that (i) excitons and F centres transfer energy to Cr$^{3+}$ and (ii) Cr($^2$E$_g$)/Cr($^4$T$_{2g}$) and F-centres/Cr$^{3+}$ PL intensity ratios underwent a linear dependence on the grain size

Understanding Persistent Luminescence: Rare-Earth- and Eu2+\mathrm{Eu^{2+}}-doped Sr2MgSi2O7\mathrm{Sr_{2}MgSi_2O_7}

Similar to many other Eu2+,RE3+-co-doped persistent luminescence materials, for Sr2MgSi2O7:Eu2+,RE3+ the initial intensity and duration of persistent luminescence was also found to depend critically on the rare-earth (RE) co-doping. An enhancement of 1 - 2 orders of magnitude in these properties could be obtained by Dy3+ co-doping whereas total quenching of persistent luminescence resulted from the use of Sm3+ and Yb3+. To solve this drastic disparity, the effects of the individual RE3+ ions were studied with thermoluminescence (TL) spectroscopy to derive information about the formation of traps storing the excitation energy. The charge compensation defects were concluded to be the origin of the complex TL glow curve structure. The tuning of the band gap of the Sr2MgSi2O7 host and especially the position of the bottom of the conduction band due to the Eu2+,RE3+ co-doping was measured with the synchrotron radiation vacuum UV (VUV) excitation spectra of the Eu2+ dopant. The model based on the evolution of the band gap energy with RE3+ co-doping was found to explain the intensity and duration of the persistent luminescence.</jats:p

Hydrothermal Synthesis and Structural and Spectroscopic Properties of the New Triclinic Form of GdBO₃:Eu³⁺ Nanocrystals

Triclinic Gd_1‑<i>x</i>Eu_<i>x</i>BO₃ nanophosphors have been prepared by a hydrothermal method without using additional coreagents and prior precipitation of precursor (<i>in situ</i>). The formation of the borate nanorods and their crystal structure was refined on the basis of X-ray diffraction patterns (XRD) and well confirmed using various techniques such as infrared spectroscopy (IR), Raman spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The new triclinic crystal structure (space group <i>P</i>1̅) for the GdBO₃ nanocrystals and detailed structure parameters were determined with the help of the Rietveld analysis. The spectroscopic characteristics of the synthesized nanomaterials with different concentrations of Eu³⁺ ions were defined with the use of luminescence excitation spectra as well as emission spectra and decay kinetics. The Judd–Ofelt parameters (Ω₂, Ω₄) and quantum efficiency, η, were also calculated for the more detailed analysis of Eu³⁺ spectra in the GdBO₃ host

Time-resolved VUV excited luminescence of Y2O3Y_2O_3:Yb nanoparticles

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Hydrothermal Synthesis and Structural and Spectroscopic Properties of the New Triclinic Form of GdBO₃:Eu³⁺ Nanocrystals

Triclinic Gd_1‑<i>x</i>Eu_<i>x</i>BO₃ nanophosphors have been prepared by a hydrothermal method without using additional coreagents and prior precipitation of precursor (<i>in situ</i>). The formation of the borate nanorods and their crystal structure was refined on the basis of X-ray diffraction patterns (XRD) and well confirmed using various techniques such as infrared spectroscopy (IR), Raman spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The new triclinic crystal structure (space group <i>P</i>1̅) for the GdBO₃ nanocrystals and detailed structure parameters were determined with the help of the Rietveld analysis. The spectroscopic characteristics of the synthesized nanomaterials with different concentrations of Eu³⁺ ions were defined with the use of luminescence excitation spectra as well as emission spectra and decay kinetics. The Judd–Ofelt parameters (Ω₂, Ω₄) and quantum efficiency, η, were also calculated for the more detailed analysis of Eu³⁺ spectra in the GdBO₃ host

Energy Structure and Luminescence of CeF3 Crystals

The results of the calculation of the energy band structure and luminescent research of CeF3 crystals are presented. The existence of two 5d1 and 5d2 subbands of the conduction band genetically derived from 5d states of Ce3+ ions with different effective electron masses of 4.9 me and 0.9 me, respectively, is revealed. The large electron effective mass in the 5d1 subband facilitates the localization of electronic excitations forming the 4f-5d cerium Frenkel self-trapped excitons responsible for the CeF3 luminescence. The structure of the excitation spectra of the exciton luminescence peaked at 290 nm, and the defect luminescence at 340 nm confirms the aforementioned calculated features of the conduction band of CeF3 crystals. The peculiarities of the excitation spectra of the luminescence of CaF2:Ce crystals dependent on the cerium concentration are considered with respect to the phase formation possibility of CeF3