Huayna Terraschke

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

SrAl 2 O 4 nanosized particles (NPs) undoped as well as doped with Eu and Dy were prepared by combustion synthesis for the discussion of their intensively debated spectroscopic properties. Emission spectra of SrAl 2 O 4 :Eu(,Dy) NPs are composed by a green band at 19 230 cm (520 nm) at room temperature, assigned to anomalous luminescence originated by Eu in this host lattice. At low temperatures, a blue emission band at 22 520 cm (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 4f(F J )5d(t 2g)→ 4f (S 7/2 ) transition of Eu substituting the Sr 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 4f core.Moreover, Fano antiresonances with the 6IJ (J = 9/2, 7/2) levels could be observed. In addition, the Stokes shifts (ΔE S = 1 980 cm and 5 270 cm 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 and 470 cm coupled with the electronic states could be reliably determined.

In situ luminescence analysis: a new light on monitoring calcium phosphate phase transitions

In this work, in situ luminescence analysis was applied for the first time for monitoring the phase transitions of calcium phosphate (CaP) and confirmed by synchrotron in situ X-ray diffraction in addition to in situ infrared spectroscopy, with simultaneous measurements of pH and ion conductivity. Applying doped Ce3+ and Eu3+ as local coordination sensors, the high sensitivity of their emission spectra upon the changes in the coordination sphere of the doped cation sites enabled to detect the formation of amorphous calcium phosphate (ACP) and Ca5(PO4)3OH, besides their subsequent transitions to CaHPO4·2H2O and Ca8H2(PO4)6·5H2O under real reaction conditions. Calcium phosphates are widely present in mammals and understanding their phase transitions is important to comprehend the conversion between healthy and diseased tissues. In situ luminescence measurements are advantageous for allowing monitoring these phase transitions in a fast and sensitive fashion also in conventional laboratories, independent of synchrotron radiation.

In situ monitoring metal-ligand exchange processes by optical spectroscopy and X-ray diffraction analysis: a review

Abstract Knowledge about the mechanisms involved in the structural development of solid materials at the atomic level is essential for designing rational synthesis protocols for these compounds, which may be used to improve desired technical properties, such as light emission, conductivity, magnetism, porosity or particle size, and may allow the tailored design of solid materials to generate the aforementioned properties. Recent technological advancements have allowed the combination of synchrotron-based in situ X-ray diffraction (XRD) with in situ optical spectroscopy techniques, providing researchers with remarkable opportunities to directly investigate structural changes during synthesis reactions. Among the various available methods to measure optical properties, in situ luminescence, UV/Vis absorption, and light transmission spectroscopies are highlighted here, with in situ luminescence being subdivided into in situ luminescence analysis of coordination sensors (ILACS) and time-resolved laser fluorescence spectroscopy (TRLFS). This article consists of a review of 122 references exploring various aspects of in situ analyses, with particular emphasis on the use of XRD-combined techniques in the study of metal-ligand exchange processes during the formation, phase transitions and decomposition of solid materials, including complexes, coordination polymers, metal-organic frameworks, nanoparticles and polyoxo- or chalcogenide metallates. We will then conclude with an exploration of future trends in this exciting research field.

Monitoring the mechanism of formation of [Ce(1,10-phenanthroline)2(NO3)3] by in situ luminescence analysis of 5d–4f electronic transitions

This work introduces the application of the in situ luminescence analysis of coordination sensors (ILACS) technique for monitoring the emission of Ce3+ 5d–4f electronic transitions under real reaction conditions during the formation of [Ce(phen)2(NO3)3] (phen = 1,10-phenanthroline). The mechanism of formation indicated by the ILACS data was confirmed by several additional methods, including ex situ and synchrotron-based in situ X-ray diffraction (XRD) analysis, in situ light transmission, and in situ infrared (IR) spectroscopy, among others. Initially, the in situ luminescence measurements presented a broad emission band at 415–700 nm, which was assigned to the Ce3+ ions in ethanolic solution. Upon the addition of the phen solution to the reactor, a gradual shift of the emission band to lower energies (500–900 nm) was observed. This occurs due to the changes in the Ce3+ coordination environment during its incorporation into the solid [Ce(phen)2(NO3)3] complex. In situ IR measurements during the crystallization of [Ce(phen)2(NO3)3] confirmed the kinetics of the crystallization process by detecting changes in the phen and nitrate vibrations at e.g. 842 and 1301 cm−1, respectively. Simultaneous in situ XRD measurements confirmed the induction time of approximately 3 minutes after the addition of the phen solution, previously detected by the in situ luminescence measurements, coinciding with the onset of the [Ce(phen)2(NO3)3] Bragg reflections. In situ monitoring of events occurring during the formation of solid materials is a crucially important step for developing rational synthesis approaches and for tailoring structure-related properties, such as luminescence.

Cd(II) and Zn(II) thiocyanate coordination compounds with 3-ethylpyridine: synthesis, crystal structures and properties

Abstract Reaction of Cd(NCS)2 and Zn(NCS)2 with 3-ethylpyridine leads to the formation of compounds of compositions M(NCS)2(3-ethylpyridine)4 (M=Cd, 1-Cd; Zn, 1-Zn) and M(NCS)2(3-ethylpyridine)2 (M=Cd, 2-Cd; Zn, 2-Zn). 1-Cd and 1-Zn are isotypic and form discrete complexes in which the metal cations are octahedrally coordinated by two trans-coordinating N-bonded thiocyanate anions and four 3-ethylpyridine co-ligands. In 2-Cd the cations are also octahedrally coordinated but linked into chains by pairs of μ-1,3-bridging anionic ligands. 2-Zn is built up of discrete complexes, in which the Zn cation is tetrahedrally coordinated by two N-bonded thiocyanate anions and two 3-ethylpyridine co-ligands. Compounds 1-Cd, 2-Cd and 2-Zn can be prepared in a pure state, whereas 1-Zn is unstable and transforms on storage into 2-Zn. If 1-Cd and 1-Zn are heated, a transformation into 2-Cd, respectively 2-Zn is observed. Luminescence measurements reveal that 1-Cd, 2-Cd and 2-Zn emit light in the blue spectral range with maxima at, respectively, 21724, 21654 and 22055 cm−1, assigned to ligand-based luminescence.