Prospecting Lighting Applications with Ligand Field Tools and Density Functional Theory: A First-Principles Account of the 4f(7)-4f(6)5d(1) Luminescence of CsMgBr3:Eu(2+)

Garnet phosphors for white-light-emitting diodes: modification and calculation

Herein, we outline our recent research progress in the modification and the first-principles calculations of garnet phosphors which should be helpful in guiding scientists to discover novel garnet phosphors for emerging applications.

Underestimated Color Centers: Defects as Useful Reducing Agents in Lanthanide-Activated Luminescent Materials

Inorganic hosts, such as SrB4 O7 or certain nitrides, intrinsically stabilize Eu2+ even when the dopant is an Eu3+ -based precursor and reducing conditions are not employed in the synthesis. Although this concept is well known in the synthesis of phosphorescent materials, the mechanistic details are scarcely understood. Herein, we demonstrate that trapped charge carriers, such as color centers, can also act as redox partners to stabilize certain oxidation states of activators. Eu-activated CsMgCl3 and CsMgBr3 are used as examples. Upon doping with EuCl3 and in the absence of reducing conditions during the synthesis, dominant cyan or green luminescence from Eu2+ ions was observed. Photoluminescence spectroscopy at 10 K revealed that the reduction is correlated to color centers localized at defects. Although defects are typically undesired in phosphors, we have shown that their role may be underestimated and they could be used on purpose in the preparation of selected inorganic phosphors.

Probing a variation of the inverse-trans-influence in americium and lanthanide tribromide tris(tricyclohexylphosphine oxide) complexes

The synthesis, characterization, and theoretical analysis of meridional americium tribromide tris(tricyclohexylphosphine oxide), mer-AmBr3(OPcy3)3, has been achieved and is compared with its early lanthanide (La to Nd) analogs. The data show that homo trans ligands display significantly shorter bonds than the cis or hetero trans ligands. This is particularly pronounced in the americium compound. DFT along with multiconfigurational CASSCF calculations show that the contraction of the bonds relates qualitatively with overall covalency, i.e. americium shows the most covalent interactions compared to lanthanides. However, the involvement of the 5p and 6p shells in bonding follows a different order, namely cerium > neodymium ∼ americium. This study provides further insight into the mechanisms by which ITI operates in low-valent f-block complexes.

Electronic Structure and Photoluminescence Properties of Eu(η9-C9H9)2

The electronic structure of Eu²⁺ compounds results from a complex combination of strongly correlated electrons and relativistic effects as well as weak ligand-field interaction. There is tremendous interest in calculating the electronic structure as nowadays the Eu²⁺ ion is becoming more and more crucial, for instance, in lighting technologies. Recently, interest in semiempirical methods to qualitatively evaluate the electronic structure and to model the optical spectra has gained popularity, although the theoretical methods strongly rely upon empirical inputs, hindering their prediction capabilities. Besides, ab initio multireference models are computationally heavy and demand very elaborative theoretical background. Herein, application of the ligand-field density functional theory (LFDFT) method that is recently available in the Amsterdam Modeling Suite is shown: (i) to elucidate the electronic structure properties on the basis of the multiplet energy levels of Eu configurations 4f⁷ and 4f⁶5d¹ and (ii) to model the optical spectra quite accurately if compared to the conventional time-dependent density functional theory tool. We present a theoretical study of the molecular Eu(η⁹-C₉H₉)₂ complex and its underlying photoluminescence properties with respect to the Eu 4f-5d electron transitions. We model the excitation and emission spectra with good agreement with the experiments, opening up the possibility of modeling lanthanides in complex environment like nanomaterials by means of LFDFT at much-reduced computational resources and cost.

Insights into the complexity of the excited states of Eu-doped luminescent materials

Multiconfigurational ab initio embedded-cluster methods give a detailed view of the excited states of Eu-doped luminescent materials, improving the understanding of their structure and how it is affected by changing the host's chemical composition.

Electronic fine structure calculation of metal complexes with three-open-shell s, d, and p configurations

The ligand field density functional theory (LFDFT) algorithm is extended to treat the electronic structure and properties of systems with three-open-shell electron configurations, exemplified in this work by the calculation of the core and semi-core 1s, 2s, and 3s one-electron excitations in compounds containing transition metal ions. The work presents a model to non-empirically resolve the multiplet energy levels arising from the three-open-shell systems of non-equivalent ns, 3d, and 4p electrons and to calculate the oscillator strengths corresponding to the electric-dipole 3d ^m  → ns ¹3d ^m 4p ¹ transitions, with n = 1, 2, 3 and m = 0, 1, 2, …, 10 involved in the s electron excitation process. Using the concept of ligand field, the Slater-Condon integrals, the spin-orbit coupling constants, and the parameters of the ligand field potential are determined from density functional theory (DFT). Therefore, a theoretical procedure using LFDFT is established illustrating the spectroscopic details at the atomic scale that can be valuable in the analysis and characterization of the electronic spectra obtained from X-ray absorption fine structure or electron energy loss spectroscopies.

Charge transfer induced energy storage in CaZnOS:Mn – insight from experimental and computational spectroscopy

A spectroscopic study shows that energy storage prior to mechanoluminescence and thermoluminescence in CaZnOS:Mn can be effectuated by a ligand-to-Mn charge transfer.

Decay times of the spin-forbidden and spin-enabled transitions of Yb2+ doped in CsCaX3 and CsSrX3 (X = Cl, Br, I)

In this article, a detailed analysis of the structure–property correlation of the decay times of the spin-forbidden and spin-enabled transitions of Yb²⁺ in the halidoperovskites CsCaX₃ and CsSrX₃ (X = Cl, Br, I) is presented.

A non-empirical calculation of 2p core-electron excitation in compounds with 3d transition metal ions using ligand-field and density functional theory (LFDFT)

It is shown that LFDFT can be used to simulate the optical spectrum of 2p core-electron excitation in compounds with 3d transition metal ions.

On the calculation of multiplet energies of three-open-shell 4f135fn6d1electron configuration by LFDFT: modeling the optical spectra of 4f core-electron excitation in actinide compounds

My presentation relates the modeling of X-ray absorption spectra of actinides, exemplified here by the study of U⁴⁺ion with configuration 4f¹³5f²6d¹.

Core electron excitations in U(4+): modelling of the nd(10)5f(2)→nd(9)5f(3) transitions with n = 3, 4 and 5 by ligand field tools and density functional theory

Ligand field density functional theory (LFDFT) calculations have been used to model the uranium M4,5, N4,5 and O4,5-edge X-ray absorption near edge structure (XANES) in UO2, characterized by the promotion of one electron from the core and the semi-core 3d, 4d and 5d orbitals of U(4+) to the valence 5f. The model describes the procedure to resolve non-empirically the multiplet energy levels originating from the two-open-shell system with d and f electrons and to calculate the oscillator strengths corresponding to the dipole allowed d(10)f(2)→ d(9)f(3) transitions appropriate to represent the d electron excitation process. In the first step, the energy and UO2 unit-cell volume corresponding to the minimum structures are determined using the Hubbard model (DFT+U) approach. The model of the optical properties due to the uranium nd(10)5f(2)→nd(9)5f(3) transitions, with n = 3, 4 and 5, has been tackled by means of electronic structure calculations based on the ligand field concept emulating the Slater-Condon integrals, the spin-orbit coupling constants and the parameters of the ligand field potential needed by the ligand field Hamiltonian from Density Functional Theory. A deep-rooted theoretical procedure using the LFDFT approach has been established for actinide-bearing systems that can be valuable to compute targeted results, such as spectroscopic details at the electronic scale. As a case study, uranium dioxide has been considered because it is a nuclear fuel material, and both atomic and electronic structure calculations are indispensable for a deeper understanding of irradiation driven microstructural changes occurring in this material.

Photoluminescence properties of Yb2+ ions doped in the perovskites CsCaX3 and CsSrX3 (X = Cl, Br, and I) – a comparative study

Photoluminescence spectra of Yb²⁺ ions doped into CsCaX₃ and CsSrX₃ (X = Cl, Br, and I) depict a manifold of transitions in high resolution, which allows a detailed understanding of the optical properties of divalent lanthanide ions in perovskite host lattices.