Analysis of Ligand Field Effects in Europium(III) Phosphates

Abstract

Optical spectra (powder reflectance, UV/Vis/NIR region), and temperature dependent magnetic behavior (χ, μ/μB) were recorded for the series of anhydrous europium(III) phosphates EuIII3O3(PO4), EuIIIPO4, EuIII2P4O13, lt‐ and ht‐EuIII(PO3)3, and EuIIIP5O14. By modeling within the AOM framework, the experimental data can be related to the ligand‐field splitting experienced by the Eu3+ ions in the various mainly low‐symmetry coordination environments. Our study confirms the well‐established relation eσ(Eu3+–O2–) ~ d(Eu3+–O2–)–7.0 between the AOM parameter and the interatomic distance. In addition it is shown that eσ(Eu3+–O2–) depends strongly on the highly variable polarizability of the oxygen ligator atoms. This polarizability can be related to the optical basicity Λ of the various phosphates.

Magnetism Studies of Bis(acyl)phosphide-Supported Eu3+and Eu2+Complexes

“…The ground-state term symbol for the Eu 3+ ion is 7 F, which is split into seven different J states ( 7 F 0‑6 ) by spin–orbit coupling, λ. The 7 F 0 state is the ground state and the first excited state, 7 F 1 , is typically found to lie approximately 350 cm –1 above the 7 F 0 ground state. − This 7 F 1 excited state can therefore be thermally populated and can also mix, via out-of-state spin–orbit coupling, with the 7 F 0 ground state. − The latter effect leads to TIP. The full spin-Hamiltonian is given by eq .25ex2ex Ĥ = Ĥ Zeeman + Ĥ SO + Ĥ CF with the 7 F 1 excited state being split in zero applied magnetic field by a low-symmetry crystal field described by the following Hamiltonian , .25ex2ex Ĥ CF = ∑ i = 1 N ∑ k = 2 , 4 , 6 ∑ q = − k k σ i k B k i q θ k Ô k i q …”

“…We have assumed an axial distortion using the crystal field parameter B 2 0 (θ 2 = −1/5), 62 which is related to the axial zero-field splitting (ZFS) parameter D by 63 The magnitude and sign of D are correlated with the symmetry of the Eu 3+ complex, and the magnitude of the zerofield splitting appears to correlate with the bond length asymmetry in Eu 3+ oxo-complexes. 49,59,60,63,64 Here, a positive value of D has the m j = 0 components of the 7 F 1 excited state lying below the m j = ±1 component. The best fit of eq 3 to the data for Eu( mes BAP) 3 (thf) 2 yielded λ = 363 cm −1 and D = 46.6 (−40.0) cm −1 (B 2 0 = −15.5 (13.3) cm −1 ) with a small (1.94%) monomeric Eu 2+ impurity (Figure 5, Table 2).…”

A Theoretical Framework for Ratiometric Single Ion Luminescent Thermometers—Thermodynamic and Kinetic Guidelines for Optimized Performance

“…Usage of wavefunction-based post-Hartree-Fock approaches resulted in LUMPAC (Luminescence Package) [228,229] that employs semiempirical wavefunction methods and incorporates ORCA as a graphical user interface. [230,231] Recently, also ab initio multiconfigurational embedded cluster methods with a high level account of relativistic effects have been reported for Eu 3+ and Tb 3+ in cubic symmetries by Joos et al [232,233] Finally, the different approach by the angular overlap framework of ligand field theory [234][235][236] led to the development of the currently optimized program package BonnMag, [237][238][239][240][241] which allows for simultaneous ligand field and intensity calculations of lanthanide-based spectra even at lower symmetries than cubic ones. All those packages have the potential to perform computational studies on novel thermometers and give predictive tools at hand to facilitate experimental trial-and-error attempts and support the development of next-generation luminescence thermometers based on lanthanide dopants.…”

“…The preconstant C can be fixed by independent luminescence decay experiments at temperatures below T c . In the special case of trivalent lanthanides, both C and the emission branching ratios can alternatively be determined by Judd‐Ofelt theory with, e.g., the packages RELIC, [ 219 ] JOES, [ 220 ] LUMPAC [ 228,229 ] or, in principle also BonnMag [ 237–241 ] (see Equation 21). On the other hand, C can be independently obtained from the intercept of a Boltzmann plot in the validity regime of the Boltzmann equilibrium (see Figure 12), since …”

Understanding Optical Absorption Spectra and Magnetic Behavior of a Wide Range of Samarium(III) Oxo‐Compounds: Analysis of the Ligand‐Field Effects

“…However, no nephelauxetic effect (Slater-Condon-Shortley (SCS) parameters and ζ are constant for the whole series) was observed. This finding is even more surprising since the series of compounds covers a wide range of optical basicity [15,10] (Λ(EuP 5 O 14 ) = 0.41, Λ(Eu 2 O 3 ) = 1.10). In this context we are aiming for a detailed understanding of LF effects for all 4f n systems (1 � n � 13), with 4f 6 and 4f 5 for europium(III) and samarium(III), respectively, being the most complex in the series due to the small energy gap between the electronic ground and the first excited state.…”