Decay times of the spin-forbidden and spin-enabled transitions of Yb 2+ doped in CsCaX 3 and CsSrX 3 (X = Cl, Br, I)

© the Owner Societies 2017. In this paper, a systematic study of the decay times of the spin-enabled and spin-forbidden transitions of Yb 2+ doped into the halidoperovskites CsMX 3 (M = Ca, Sr; X = Cl, Br, I) is presented. The spin-forbidden transitions are characterized by ms decay times, which are typical for Yb 2+ . On the contrary, the spin-enabled transitions show much shorter decay times in the range of μs and have so far only been rarely observed. These results allow detailed conclusions about systematics of the decay times of Yb 2+ doped in similar compounds and their correlation to the local structure of the coordination sphere of Yb 2+ as well as the role of vibrational interaction between the excited high spin (HS) and low spin (LS) states. The halidoperovskites are ideally suited as host lattices in this context and may work as text book examples due to their comparable structures, which allows a detailed interpretation of the decay times in relation to the local structure. An understanding of the impact of the composition and structure of the host material on the decay times of Yb 2+ will be of relevance for future applications of this activator in scintillators or lighting materials

ABiO 2 X (A = Cd, Ca, Sr, Ba, Pb; X = halogen) Sillen X1 Series: Polymorphism Versus Optical Properties

International audienceThe Sillen X1 series of Bi 3+ A 2+ O 2 X (A = Cd, Ca, Sr, Ba, Pb; X = Cl, Br, I) compounds is composed of three main crystallographic types, namely, the tetragonal form (space group (S.G.) I4/mmm), the orthorhombic form (S.G. Cmcm), and the monoclinic form (S.G. P2 1 /m). Because of Bi 3+ /A 2+ disorder the Bi 3+ based photoluminescence (PL) of the tetragonal polytypes is quenched at room temperature (RT). In the two other ordered forms, the Bi−O−Bi connectivity is different but limited, such that bluish/ greenish emission occurs at RT in the monoclinic CdBiO 2 Cl and CaBiO 2 Cl and orthorhombic SrBiO 2 Cl and BaBiO 2 Cl phases. The crystal structure of BaBiO 2 Br was refined in the orthorhombic Cmcm space group and also shows RT emission. Focusing on the RT luminescent activity as a key parameter, the PL active compounds were investigated by means of density functional theory calculations and UV−visible reflectance spectroscopy. The influence of A and X ions on the excitation energy is discussed by analyzing the A−O−Bi and Bi−X bonding schemes and gives some insights for rational tuning of both the excitation and emission energies

Impact of 1,10-Phenanthroline-Induced Intermediate Valence on the Luminesence of Divalent Europium Halides

Starting from EuX2 (X = Cl, Br, I), we systematically investigated a variety of divalent europium complexes containing bidentate 1,10-phenanthroline (Phen) ligands. Depending on the Eu/Phen ratio, mono-, di-, and polynuclear complexes are formed, with the latter yielding one-dimensional infinity 1[EuBr2(phen)] chains. Seven new divalent europium complexes, [Eu(phen)4(H2O)]Br2 center dot 2MeCN, [Eu(phen)4]I2 center dot 1.7Tol, [EuBr(phen)3]2Br2 center dot 4MeCN, [EuCl2(phen)2]2 center dot 2MeCN, [EuBr2(phen)2]2, [EuI2(phen)2]2, and [EuBr2(phen)]x, are presented in this work. All species show remarkable optical properties based on a partial electron transfer from the EuII center to the Phen ligand. The photophysical characterization is further supported by electrochemistry studies in order to describe the intermediate valence of the Eu center

SrAl2O4:Eu2+(,Dy3+) Nanosized Particles: Synthesis and Interpretation of Temperature-Dependent Optical Properties

SrAl2O4 nanosized particles (NPs) undoped as well as doped with Eu2+ and Dy3+ were prepared by combustion synthesis for the discussion of their intensively debated spectroscopic properties. Emission spectra of SrAl2O4:Eu2+(,Dy3+) NPs are composed by a green band at 19 230 cm−1 (520 nm) at room temperature, assigned to anomalous luminescence originated by Eu2+ in this host lattice. At low temperatures, a blue emission band at 22 520 cm−1 (444 nm) is observed. Contrary to most of the interpretations provided in the literature, we assign this blue emission band very reliably to a normal 4f6(7FJ)5d(t2g)→4f7(8S7/2) transition of Eu2+ substituting the Sr2+ sites. This can be justified by the presence of a fine structure in the excitation spectra due to the different 7FJ levels (J=0⋯6) of the 4f6 core. Moreover, Fano antiresonances with the 6IJ (J=9/2,7/2) levels could be observed. In addition, the Stokes shifts (ΔES=1 980 cm−1 and 5 270 cm−1 for the blue and green emission, resp.), the Huang-Rhys parameters of S=2.5 and 6, and the average phonon energies of ħω=480 cm-1 and 470 cm−1 coupled with the electronic states could be reliably determined

Oscillating Emission of [2]Rotaxane Driven by Chemical Fuel

A molecular shuttle consisting of a dibenzo-24-crown-8 macrocycle and an axle with two degenerate peripheral triazolium stations, a central dibenzyl ammonium station, and two anthracenes stoppers was exposed to 2-cyano-2-phenylpropanoic acid as a chemical fuel. Protonation/deprotonation of the amine reversibly switches the rotaxane from a static and little emissive to a dynamic fluorescent shuttling device, the latter exhibiting rapid motion (15 kHz at 25 °C). Four fuel cycles were run

Physical Properties of Superbulky Lanthanide Metallocenes:Synthesis and Extraordinary Luminescence of [Eu-II(Cp-BIG)(2)] (Cp-BIG=(4-nBu-C6H4)(5)-Cyclopentadienyl)

The superbulky deca-aryleuropocene [Eu(Cp-BIG)(2)], Cp-BIG=(4-nBu-C6H4)(5)-cyclopentadienyl, was prepared by reaction of [Eu(dmat)(2)(thf)(2)], DMAT=2-Me2N--Me3Si-benzyl, with two equivalents of (CpH)-H-BIG. Recrystallizyation from cold hexane gave the product with a surprisingly bright and efficient orange emission (45% quantum yield). The crystal structure is isomorphic to those of [M(Cp-BIG)(2)] (M=Sm, Yb, Ca, Ba) and shows the typical distortions that arise from (CpCpBIG)-Cp-BIG attraction as well as excessively large displacement parameter for the heavy Eu atom (U-eq=0.075). In order to gain information on the true oxidation state of the central metal in superbulky metallocenes [M(Cp-BIG)(2)] (M=Sm, Eu, Yb), several physical analyses have been applied. Temperature-dependent magnetic susceptibility data of [Yb(Cp-BIG)(2)] show diamagnetism, indicating stable divalent ytterbium. Temperature-dependent Eu-151 Mossbauer effect spectroscopic examination of [Eu(Cp-BIG)(2)] was examined over the temperature range 93-215K and the hyperfine and dynamical properties of the Eu-II species are discussed in detail. The mean square amplitude of vibration of the Eu atom as a function of temperature was determined and compared to the value extracted from the single-crystal X-ray data at 203K. The large difference in these two values was ascribed to the presence of static disorder and/or the presence of low-frequency torsional and librational modes in [Eu(Cp-BIG)(2)]. X-ray absorbance near edge spectroscopy (XANES) showed that all three [Ln(Cp-BIG)(2)] (Ln=Sm, Eu, Yb) compounds are divalent. The XANES white-line spectra are at 8.3, 7.3, and 7.8eV, for Sm, Eu, and Yb, respectively, lower than the Ln(2)O(3) standards. No XANES temperature dependence was found from room temperature to 100K. XANES also showed that the [Ln(Cp-BIG)(2)] complexes had less trivalent impurity than a [EuI2(thf)(x)] standard. The complex [Eu(Cp-BIG)(2)] shows already at room temperature strong orange photoluminescence (quantum yield: 45%): excitation at 412nm (24270cm(-1)) gives a symmetrical single band in the emission spectrum at 606nm ((max)=16495cm(-1), FWHM: 2090cm(-1), Stokes-shift: 2140cm(-1)), which is assigned to a 4f(6)5d(1)4f(7) transition of Eu-II. These remarkable values compare well to those for Eu-II-doped ionic host lattices and are likely caused by the rigidity of the [Eu(Cp-BIG)(2)] complex. Sharp emission signals, typical for Eu-III, are not visible

ABiO₂X (A = Cd, Ca, Sr, Ba, Pb; X = halogen) <i>Sillen</i> X1 Series: Polymorphism Versus Optical Properties

The <i>Sillen</i> X1 series of Bi³⁺A²⁺O₂X (A = Cd, Ca, Sr, Ba, Pb; X = Cl, Br, I) compounds is composed of three main crystallographic types, namely, the tetragonal form (space group (S.G.) <i>I</i>4<i>/mmm</i>), the orthorhombic form (S.G. <i>Cmcm</i>), and the monoclinic form (S.G. <i>P</i>2₁/<i>m</i>). Because of Bi³⁺/A²⁺ disorder the Bi³⁺ based photoluminescence (PL) of the tetragonal polytypes is quenched at room temperature (RT). In the two other ordered forms, the Bi–O–Bi connectivity is different but limited, such that bluish/greenish emission occurs at RT in the monoclinic CdBiO₂Cl and CaBiO₂Cl and orthorhombic SrBiO₂Cl and BaBiO₂Cl phases. The crystal structure of BaBiO₂Br was refined in the orthorhombic <i>Cmcm</i> space group and also shows RT emission. Focusing on the RT luminescent activity as a key parameter, the PL active compounds were investigated by means of density functional theory calculations and UV–visible reflectance spectroscopy. The influence of A and X ions on the excitation energy is discussed by analyzing the A–O–Bi and Bi–X bonding schemes and gives some insights for rational tuning of both the excitation and emission energies

Heterometallic Europium Disiloxanediolates: Synthesis, Structural Diversity, and Photoluminescence Properties

This contribution presents a full account of a structurally diverse class of heterometallic europium disiloxanediolates. The synthetic protocol involves <i>in situ</i> metalation of (HO)­SiPh₂OSiPh₂(OH) (<b>1</b>) with either ^<i>n</i>BuLi or KN­(SiMe₃)₂ followed by treatment with EuCl₃ in suitable solvents such as 1,2-dimethoxyethane (DME) or tetrahydrofuran (THF). Reaction of EuCl₃ with 2 equiv of (LiO)­SiPh₂OSiPh₂(OLi) in DME afforded the Eu^III bis­(disiloxanediolate) “ate” complex [{(Ph₂SiO)₂O}₂{Li­(DME)}₃]­EuCl₂ (<b>2</b>), which upon attempted reduction with Zn gave the tris­(disiloxanediolate) [{(Ph₂SiO)₂O}₃{Li­(DME)}₃]Eu (<b>3</b>). Treatment of EuCl₃ with (LiO)­SiPh₂OSiPh₂(OLi) in a molar ratio of 1:2 yielded both the ate complex [{(Ph₂SiO)₂O}₃Li­{Li­(THF)₂}­{Li­(THF)}]­EuCl·Li­(THF)₃ (<b>4</b>) and the LiCl-free europium­(III) complex [{(Ph₂SiO)₂O}₂{Li­(THF)₂}₂]­EuCl (<b>5</b>). Compound <b>5</b> was found to exhibit a brilliant red triboluminescence. When (KO)­SiPh₂OSiPh₂(OK) was used as starting material in a 3:1 reaction with EuCl₃, the Eu^III tris­(disiloxanediolate) [{(Ph₂SiO)₂O}₃{K­(DME)}₃]Eu (<b>6</b>) was isolated. Attempted ligand transfer between <b>5</b> and (DAD^Dipp)₂Ba­(DME) (DAD^Dipp = <i>N</i>,<i>N</i>′-bis­(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene) afforded the unique mixed-valent Eu^III/Eu^II disiloxanediolate cluster [(Ph₂SiO)₂O]₆Eu^II₄Eu^III₂Li₄O₂Cl₂ (<b>7</b>). All new complexes were structurally characterized by X-ray diffraction. Photoluminescence studies were carried out for complex <b>5</b> showing an excellent color quality, due to the strong ⁵D₀→⁷F₂ transition, but a weak antenna effect