Properties Design: Prediction and Experimental Validation of the Luminescence Properties of a New EuII -Based Phosphor

A theoretical model that allows to predict, for the first time, the luminescence properties of a new phosphor (BaSnSi₃ O₉ :Eu²⁺ ) is presented. The predicted emission wavelength, 488 nm with a 64 nm bandwidth, was confirmed by subsequent experimental work. The method consists in a multi-electron Hamiltonian parametrized from ab initio calculations. The luminescence properties of other similar compounds (i.e., BaHfSi₃ O₉ :Eu²⁺ and BaZrSi₃ O₉ :Eu²⁺ ), for which there is already experimental information, were also correctly reproduced.

The Electronic States of U(4+) in U(PO4)Cl: An Example for Angular Overlap Modeling of 5f(n) Systems

Detailed experimental data on UPO4Cl comprising single-crystal UV/vis/NIR spectra and temperature-dependent magnetic susceptibilities form the basis for the investigation of the electronic structure of the U(4+) cation in UPO4Cl. For modeling of the observed physical properties the angular overlap model (AOM) was successfully employed. The computations were performed using the newly developed computer program BonnMag. The calculations show that all electronic transitions and the magnetic susceptibility as well as its temperature dependence are well-reproduced within the AOM framework. Using Judd-Ofelt theory BonnMag allows estimation of the relative absorption coefficients of the electronic transitions with reasonable accuracy. Ligand field splitting for states originating from f-electron configurations are determined. Slater-Condon-Shortley parameters and the spin-orbit coupling constant for U(4+) were taken from literature. The good transferability of AOM parameters for U(4+) is confirmed by calculations of the absorption spectra of UP2O7 and (U2O)(PO4)2. The effect of variation of the fit parameters is investigated. AOM parameters for U(4+) (5f) are compared to those of the rare-earth elements (4f) and transition metals (3d).

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.

Effect of Ca(2+) codoping on the Eu(2+) luminescence properties in the Sr2Si5N8 host lattice: a theoretical approach

Here we report a theoretical analysis of the luminescence properties of Sr2Si5N8 host lattices codoped with Ca(2+) and Eu(2+). These systems have been first synthesized by Li et al. [J. Solid State Chem., 2008, 181, 515], who have found that Ca(2+) doping provokes a red-shifting of the emission peak of Eu(2+), from 620 nm to 643 nm. However, the mechanism that drives this shift is still unclear from experimental data. Based on density functional theory and ligand field analysis, we study the structure, stability, and emission properties of Eu(2+) embedded in the (Sr1-xCax)2Si5N8 host lattice. Our results provide a full explanation of the experimental data and the methodology could constitute a valuable tool for the design of phosphors with tunable emission spectra.

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+)

The most efficient way to provide domestic lighting nowadays is by light-emitting diodes (LEDs) technology combined with phosphors shifting the blue and UV emission toward a desirable sunlight spectrum. A route in the quest for warm-white light goes toward the discovery and tuning of the lanthanide-based phosphors, a difficult task, in experimental and technical respects. A proper theoretical approach, which is also complicated at the conceptual level and in computing efforts, is however a profitable complement, offering valuable structure-property rationale as a guideline in the search of the best materials. The Eu(2+)-based systems are the prototypes for ideal phosphors, exhibiting a wide range of visible light emission. Using the ligand field concepts in conjunction with density functional theory (DFT), conducted in nonroutine manner, we develop a nonempirical procedure to investigate the 4f(7)-4f(6)5d(1) luminescence of Eu(2+) in the environment of arbitrary ligands, applied here on the CsMgBr3:Eu(2+)-doped material. Providing a salient methodology for the extraction of the relevant ligand field and related parameters from DFT calculations and encompassing the bottleneck of handling large matrices in a model Hamiltonian based on the whole set of 33,462 states, we obtained an excellent match with the experimental spectrum, from first-principles, without any fit or adjustment. This proves that the ligand field density functional theory methodology can be used in the assessment of new materials and rational property design.

Ligand field density functional theory for the prediction of future domestic lighting

We deal with the computational determination of the electronic structure and properties of lanthanide ions in complexes and extended structures having open-shell f and d configurations. Particularly, we present conceptual and methodological issues based on Density Functional Theory (DFT) enabling the reliable calculation and description of the f → d transitions in lanthanide doped phosphors. We consider here the optical properties of the Pr(3+) ion embedded into various solid state fluoride host lattices, for the prospection and understanding of the so-called quantum cutting process, being important in the further quest of warm-white light source in light emitting diodes (LED). We use the conceptual formulation of the revisited ligand field (LF) theory, fully compatibilized with the quantum chemistry tools: LFDFT. We present methodological advances for the calculations of the Slater-Condon parameters, the ligand field interaction and the spin-orbit coupling constants, important in the non-empirical parameterization of the effective Hamiltonian adjusted from the ligand field theory. The model shows simple procedure using less sophisticated computational tools, which is intended to contribute to the design of modern phosphors and to help to complement the understanding of the 4f(n) → 4f(n-1)5d(1) transitions in any lanthanide system.

The angular overlap model extended for two-open-shell f and d electrons

We discuss the applicability of the Angular Overlap Model (AOM) to evaluate the electronic structure of lanthanide compounds, which are currently the subject of incredible interest in the field of luminescent materials. The functioning of phosphors is well established by the f-d transitions, which requires the investigation of both the ground 4f(n) and excited 4f(n-1)5d(1) electron configurations of the lanthanides. The computational approach to the problem is based on the effective Hamiltonian adjusted from ligand field theory, but not restricted to it. The AOM parameterization implies the chemical bonding concept. Focusing our interest on this interaction, we take the advantages offered by modern computational tools to extract AOM parameters, which ensure the transparency of the theoretical determination and convey chemical intuitiveness of the non-empirical results. The given model contributes to the understanding of lanthanides in modern phosphors with high or low site symmetry and presents a non-empirical approach using a less sophisticated computational procedure for the rather complex problem of the ligand field of both 4f and 5d open shells.

Tailoring the optical properties of lanthanide phosphors: prediction and characterization of the luminescence of Pr(3+)-doped LiYF4

We present a theoretical work detailing the electronic structure and the optical properties of (PrF8)(5-) embedded in LiYF4, complementing the insight with data that are not available by experimental line. The local distortions due to the embedding of the lanthanide ion in the sites occupied in the periodic lattice by smaller yttrium centres, not detectable in regular X-ray analyses, are reproduced with the help of geometry optimization. Then, based on the local coordination environment, the relation structure-optical properties is constructed by Density Functional Theory computations in conjunction with the ligand field theory analyses (LFDFT) determining the [Xe]4f(2)→ [Xe]4f(1)5d(1) transitions. In previous instances we analysed rather symmetric systems, here facing the complexity of low symmetry cases, treated in the Wybourne ligand field parameterization and in the Angular Overlap Model (AOM) frame. A very important improvement at the AOM level is the consideration of the f-d mixing that brings coupling term of odd-even nature, essential for the realistic description of the asymmetric coordination centres. Furthermore, we introduce now a principle for modelling the emission intensity. The results are in agreement with available experimental findings. The relevance of the modelling has a practical face in the rational design of optimal luminescent materials needed in domestic lightening and also an academic side, revisiting with modern computational tools areas incompletely explored by the standard ligand field theories.

Synthesis, Crystal Structure and Magnetic Behaviour of Dimeric and Polymeric Gadolinium Trifluoroacetate Complexes

The gadolinium(III) trifluoroacetates ((CH3)2NH2)[Gd(CF3COO)4] (1), ((CH3)3NH)[Gd(CF3 COO)4(H2O)] (2), Gd(CF3COO)3(H2O)3 (3) as well as Gd2(CF3COO)6(H2O)2(phen)3 · C2H5OH (4) (phen = 1,10-phenanthroline) were synthesized and structurally characterized by X-ray crystallography. These compounds crystallize in the space group P1̅ (No. 2, Z = 2) (1, 2 and 4) and P 21/c (No. 14, Z = 4) (3), respectively, with the following lattice constants 1: a = 884.9(2), b = 1024.9(2), c = 1173.1(2) pm, α = 105.77(2), β = 99.51(2), γ = 107.93(2)°; 2: a = 965.1(1), b = 1028.6(1), c = 1271.3(2) pm, α = 111.83(2), β = 111.33(2), γ = 90.44(2)°; 3: a = 919.6(2), b = 1890.6(4), c = 978.7(2) pm, β = 113.94(2)°; 4: a = 1286.7(8), b = 1639.3(8), c = 1712.2(9) pm, α = 62.57(6), β = 84.13(5), γ = 68.28(5)°. The compounds consist of Gd3+ ions which are bridged by carboxylate groups either to chains (1 and 2) or to dimers (3 and 4). In addition to the Gd3+ dimers, compound (4) also contains monomeric Gd3+ units. The magnetic behaviour of 2 and 3 was investigated in a temperature range of 1.77 to 300 K. The magnetic data for these compounds indicate weak antiferromagnetic interactions

Darstellung und Kristallstruktur von NdSe1,9/ Preparation and Crystal Structure of NdSe1,9

NdSe1,9 has been prepared as grey, strongly reflecting platelets by reaction of elemental neodymium with selenium in the ratio 1 :2 and subsequent chemical vapour phase transport with iodine. It crystallizes in the tetragonal space group P42/n with a = 925.36(7), c = 1679.2(3) pm and Z = 20. The structure determination results in a formulation of NdSe1,9 as Nd 20(Se(I)2)8Se(I)2⃞2Se(II)20, where the defect layer built from the Se(I)2 2- and Se(I)2- ions corresponds to the F layer in the PbFCl substructure.

Zur Kristallstruktur von Ho2Se3/ On the Crystal Structure of Ho2Se3

Starting from HoSe2-x powder and holmium metal bright brownish-yellow, plate-like single crystals of Ho2Se3 could be prepared by chemical transport with AlCl3. Holmium sesquiselenide crystallizes in the Sc2S3-type structure, space group Fddd, with lattice constants a = 1140,7(2), b -812,6(1) and c = 2423,9(3) pm.

Darstellung and Kristallstruktur von [(C6H5)4As]2M(NO3)5 (M = Ho, Er, Tm, Yb) / Preparation and Crystal Structure of [(C6H5)4As]2M(NO3)5 (M = Ho, Er, Tm, Yb)

The compounds [(C6H5)4As]2M(NO3)5 (M = Ho, Er, Tm, Yb) were prepared and investigated by X-ray diffraction. It has been found that they are isotypic with [(C6H5)4As]2Eu(NO3)5. The structure was refined by single crystal data for [(C6H5)4As]2Er(NO3)5.

Zur Polymorphie von TbCI3/ Polymorphism of TbCl3

3 different modifications of TbCl3 were synthesized. TbCl, (UCl3-type), probably in a metastable state, crystallizes in space group P63/m with a = 737.63(2) pm, c = 405.71(2) pm and Z - 2. TbCl3 (PuB3-type) crystallizes in space group Cmcm with a = 384.71(6) pm, b = 1177.37(7) pm. c = 851.77(4) pm and Z = 4. h-TbCl3, the high temperature phase being stable above 790 K. crystallizes in space group P42/mnm with a = 642.51(4) pm, c = 1177.14(18) pm and Z = 4.

Die Struktur des PrCl3 bei verschiedenen Temperaturen / The Structure of PrCl3 at Different Temperatures

Structural investigations on PrCl3 were performed from room temperature down to 40 K (powder) and from room temperature down to 83 K (single crystal). Special interest was focussed on the changes of the coordination geometry of the Pr3+-ion.

Darstellung und Struktur von (CH3NH3)3PrCl6 · 2 H2O / Synthesis and Structure of (CH3NH3)3PrCl6 · 2 H2O

(CH3NH3)3PrCl6 · 2 H2O has been prepared as light green, air sensitive crystals by the reaction of PrCl3·xH2O with [CH3NH3]Cl in ethanol. The compound was characterized by crystal structure determination. Crystal data: monoclinic space group I 2/a, Z = 8. Lattice constants: a = 1963.3(4), b = 925.9(3), c = 1954.3(4) pm, β = 90.56(1)°. The compound forms [PrCl4(H2O)2]--chains where two Pr3+-ions are connected via two chlorine atoms. The magnetic behaviour of (CH3NH3)3PrCl6· 2H2O has been studied.

Neue Verbindungen der Lanthanoiden vom Typ [(C6H5)4E]MX4 · 8 H2O = P, As; M = La, Ce, Pr, Sm, Eu, Gd; X = Cl, Br) / New Lanthanide Compounds of the Type [(C6H5)4E]MX4 · 8 H2O (E = P, As; M = La, Ce, Pr, Sm, Eu, Gd; X = Cl, Br)

The compounds [(C6H5)4P]PrX4 · 8 H2O (X = Cl, Br), [(C6H5)4P]LaBr4 · 8 H2O and [(C6H5)4As]MCl4 · 8 H2O (M = La, Ce, Pr, Sm. Eu, Gd) were prepared and investigated by X-ray diffraction. The compounds were found to be isotypic with [(C6H5)4As]NdCl4 · 8 H2O, which was structurally characterized already previously. The magnetic behaviour of [(C6H5)4P]PrX4 · 8 H2O (X = Cl, Br) has been studied.

Darstellung und Kristallstruktur von Nd2SeSiO4 / Preparation and Crystal Structure of Nd2SeSiO4

Nd2SeSiO4 has been prepared as violet rod-like single crystals by reaction of elemental neodymium, selenium and iodine in the ratio 1.0:1.0:2.5 and subsequent reaction with quartz glass powder. The compound crystallizes in the orthorhombic space group Pbcm with a = 618.2(2), b = 717.4(2), c = 1102.4(2) pm and Z = 4. The structure is built up of alternating NdSe- and NdSiO4-sheets.

The theoretical account of the ligand field bonding regime and magnetic anisotropy in the DySc2N@C80 single ion magnet endohedral fullerene

Methodological advances for the treatment of electron structure and properties of the f-type ions embedded in fullerenes are presented.

Ligand field density functional theory calculation of the 4f2→ 4f15d1 transitions in the quantum cutter Cs2KYF6:Pr3+

Herein we present a Ligand Field Density Functional Theory (LFDFT) based methodology for the analysis of the 4f(n)→ 4f(n-1)5d(1) transitions in rare earth compounds and apply it for the characterization of the 4f(2)→ 4f(1)5d(1) transitions in the quantum cutter Cs2KYF6:Pr(3+) with the elpasolite structure type. The methodological advances are relevant for the analysis and prospection of materials acting as phosphors in light-emitting diodes. The positions of the zero-phonon energy corresponding to the states of the electron configurations 4f(2) and 4f(1)5d(1) are calculated, where the praseodymium ion may occupy either the Cs(+)-, K(+)- or the Y(3+)-site, and are compared with available experimental data. The theoretical results show that the occupation of the three undistorted sites allows a quantum-cutting process. However size effects due to the difference between the ionic radii of Pr(3+) and K(+) as well as Cs(+) lead to the distortion of the K(+)- and the Cs(+)-site, which finally exclude these sites for quantum-cutting. A detailed discussion about the origin of this distortion is also described.

Crystal structures of Gd2(Cl3CCOO)6(bipy)2(H2O)2 · 4 bipy, Pr(Cl3CCOO)3(bipy)2, Nd(Cl3CCOO)3(bipy)2 and Er(Cl3CCOO)3(bipy)2(H2O)

Single crystals of Gd2(Cl3CCOO)6(bipy)2 × (H2O)2 · 4 bipy, Pr(Cl3CCOO)3(bipy)2, Nd(Cl3CCOO)3 × (bipy)2 and Er(Cl3CCOO)3(bipy)2(H2O) have been obtained by reaction of the corresponding trichloroacetate salts with 2,2′-bipyridyl (bipy) in a water/ethanol (1:1) solution. Gd2(Cl3CCOO)6(bipy)2(H2O)2 · 4 bipy crystallizes in the monoclinic space group P21/c (no. 14, Z = 4, a = 1642.40(9) pm, b = 1227.36(10) pm, c = 2303.48(14) pm, β = 107.043(7)°). The Gd3+ ions are bridged to dimers by carboxylate groups and are surrounded by six oxygen and two nitrogen atoms. One 2,2′-bipyridyl molecule is coordinated to Gd3+, the two other ones are non-coordinated.

The monomeric compounds Ln(Cl3CCOO)3(bipy)2 (Ln = Pr, Nd) are isotypic with each other and crystallize in the triclinic space group P-1 (no. 2, Z = 2, Pr: a = 989.83(8) pm, b = 1032.22(8) pm, c = 1791.56(13) pm, α = 99.312(9)°, β = 102.036(9)°, γ = 99.166(9)°; Nd: a = 990.09(7) pm, b = 1030.74(8) pm, c = 1788.70(13) pm, α = 99.393(9)°, β = 102.064(8)°, γ = 99.242(9)°). The Ln3+ atom is surrounded by six oxygen and four nitrogen atoms. A chelating coordination by the carboxylate groups is observed. There are two 2,2′-bipyridyl molecules coordinated to Ln3+.

The compound Er(Cl3CCOO)3(bipy)2(H2O) crystallizes in the triclinic space group P-1 (no. 2, Z = 2, a = 1060.65(9) pm, b = 1273.35(11) pm, c = 1402.49(11) pm, α = 105.484(10)°, β = 104.504(9)°, γ = 93.712(10)°). The Er3+ ion is coordinated by four oxygen and four nitrogen atoms. There are two 2,2′-bipyridyl molecules attached to Er3+.

Synthesis, crystal structures and magnetic behaviour of dimeric and tetrameric gadolinium carboxylates with trichloroacetic acid

The novel gadolinium(III) containing compounds (CH3NH3)2[Gd2(CCl3COO)6(H2O)6](CCl3COO)2.2CCl3COOH (1) and (NH3CH3)2[Gd4(OH)4(CCl3COO)10(H2O)6].2H2O (2) were synthesized and structurally characterized by X-ray crystallography. In the crystal structure of 1 the gadolinium ions are bridged by carboxylate groups to dimers with a Gd3+ -Gd3+ distance of 420.2(3) pm. The compound crystallizes in the triclinic space group P1. In the crystal structure of the Gd3+ ions are bridged by hydroxide ions and carboxylate groups to tetramers with Gd3+ -Gd3+ distances between 380.3(1) and 388.0(1) pm. The compound crystallizes in the triclinic space group P1. The magnetic behaviour of these two compounds as well as of Gd2(CCl3COO)6(bipy)2(H2O)2.4bipy (3) (bipy = 2,2'-bipyridyl) was investigated in the temperature range 1.77-300 K. The magnetic data for these compounds indicate weak antiferromagnetic interactions.