Strategy to Probe the Local Atomic Structure of Luminescent Rare Earth Complexes by X-ray Absorption Near-Edge Spectroscopy Simulation Using a Machine Learning-Based PyFitIt Approach

Abstract

Rare earth(III) β-diketonates are highly remarkable luminophores in the visible spectral region among the rare earth compounds, owing to the efficient contribution from the 4f–4f intraconfigurational transitions. To get detailed structural insight into the RE3+ sites (RE = Eu, Gd, and Sm), X-ray absorption near-edge spectroscopy (XANES) can be very potent in probing the local chemical environment around the RE3+ ion. In this work, a PyFitIt machine learning approach was employed as a new strategy to simulate the Eu, Gd, and Sm L3-edge XANES and thereby determine the local atomic structure of the luminescence RE3+ β-diketonate complexes, [Eu(tta)3(H2O)2], [C4mim][Eu(dbm)4], [Gd(tta)3(H2O)2], and [Sm(dbm)3(phen)] (tta, 3-thenoyltrifluoroacetonate; dbm, dibenzoylmethane; phen, phenanthroline; and C4mim, 1-butyl-3-methylimidazolium bromide). Continuous Cauchy wavelet transform validated the PyFitIt calculated XANES by visualizing very efficiently the coordination geometries, composed of O and O/N backscatterers around the RE3+ (RE = Eu and Gd) and Sm3+ ions, respectively, as a pinkish-red color map in the two-dimensional images of the corresponding complexes. Extended X-ray absorption fine structure fit in Artemis also corroborated the three-dimensional structures generated by PyFitIt XANES simulation for all the compounds. Though, relatively slightly higher bond distance values for the Sm3+ complex are due to the higher atomic radius of the Sm3+ ion when compared to the Eu3+ and Gd3+ complexes. Meanwhile, higher Debye–Waller factor (σ2) values for the [C4mim][Eu(dbm)4] when compared to the [Eu(tta)3(H2O)2] indicated the structure disorder, owing to the distortion in the local geometry. It is noteworthy that the optical properties, described mainly by the Ωλ (λ = 2 and 4) 4f–4f intensity parameters, are very sensitive to the local coordination environment around the Eu3+ ion. Thus, a close agreement between the experimental and theoretically calculated Ωλ parameter values confirmed that the PyFitIt calculated square antiprismatic structures are precisely similar to the real structures of the Eu3+ complexes.

Insight into a pure spinel Co3O4 and boron, nitrogen, sulphur (BNS) tri-doped Co3O4-rGO nanocomposite for the electrocatalytic oxygen reduction reaction

“…successive change in shape of the second peak (∼2.8 Å) for the Co 3 O 4 /BNS rGO and Co 3 O 4 /rGO, and considerable decrease in the amplitude for the Co 3 O 4 /BNS rGO demonstrated clear change for Co site in second shell for these two nanocatalysts, when compared to the Co 3 O 4 . The similar result was also observed in the two-dimensional CCWT images of the Co 3 O 4 / BNS rGO and Co 3 O 4 /rGO, which were qualitatively analyzed through continuous Cauchy wavelet transform (CCWT), using MATLAB 2019b 43. The two-dimensional CCWT images of these two nanostructures showed the difference in the shape of the colormaps, corresponding to O backscattered in rst coordination shell and Co backscattered in second coordination shell, when compared to those of Co3 O 4 .…”

“…The similar result was also observed in the two-dimensional CCWT images of the Co 3 O 4 /BNS rGO and Co 3 O 4 /rGO, which were qualitatively analyzed through continuous Cauchy wavelet transform (CCWT), using MATLAB 2019b. 43 The two-dimensional CCWT images of these two nanostructures showed the difference in the shape of the colormaps, corresponding to O backscattered in first coordination shell and Co backscattered in second coordination shell, when compared to those of Co 3 O 4 . Nevertheless, the overall X-ray absorption fine structure spectroscopy (XAFS) data analyses results suggested pure cubic Co 3 O 4 phase for the Co 3 O 4 , and thus, change in the local atomic structure of the Co site for Co 3 O 4 /BNS rGO and Co 3 O 4 /rGO nanocatalysts, when compared to the Co 3 O 4 cubic lattice Fig.…”

Singlet Molecular Oxygen Generation via Unexpected Emission Color-Tunable CdSe/ZnS Nanocrystals for Applications in Photodynamic Therapy

“…The local atomic structure order, chemical composition, and nature of alloying in QDs were further unraveled in detail by X-ray absorption fine structure (XAFS) data analyses. 48 The Zn K-edge X-ray absorption electronic structure in the near edge region (XANES) spectra of QDs (I) and QDs (II) displayed a typical sharp rising edge or white line peak A at ∼9663.8 eV, followed by two lower intensity distinct peaks B and C in the multiple scattering region, within the spectral range of 50 eV above the edge, and a broader peak D from the first single-like scattering of EXAFS oscillation, manifesting the typical Zn K-edge features of the Zn site with the sulfide anion in the zinc blende cubic lattice. These spectra are significantly different from the Zn K-edge XANES of ZnSe, 6 which display two characteristic absorption peaks in the spectral region of 50 eV above the edge (Figure 2a).…”

Colloidal Quantum Dots as an Emerging Vast Platform and Versatile Sensitizer for Singlet Molecular Oxygen Generation

“…X-ray absorption spectroscopy (XAS) is a highly element-specific technique that probes efficiently the local atomic/electronic structure of the photoabsorber (metal site) in NCs . The lattice disorder, oxygen vacancies, and defects in the lattice can be probed by quantitative X-ray absorption near-edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) analyses. , The emission color of the QDs is extended over the wide visible to near-infrared (NIR) wavelength ranges, mainly due to the size-dependent quantum confinement effects, originating from the spatial confinement of electron–hole pairs (excitons) in one or more dimensions within a material, carrying a discrete electronic energy level structure when compared to the bulk material counterparts. ,,,,,,, The quantum confinement effect usually occurs in semiconductors, when the particle sizes are reduced to the same order as the exciton radius, i.e., to a few nanometers, providing modified exciton properties with a changeable bandgap in relation to the size of the nanocrystal.…”