Partly filled shells constituting anti-bonding orbitals with higher ionization energy than their bonding counterparts

Jørgensen, C.K.

doi:10.1007/bfb0116555

“…30 Because of the relatively long distance between the Ce 3+ ions, one can consider the Ce sites as nearly independent, and a cluster approach that takes into account explicitly only one Ce 3+ ion can be used to characterize the Ce−O interactions. For the two embedded clusters, the quantum chemical CASSCF/CASPT2 calculations with the effect of spin−orbit coupling were then performed to obtain the 4f 1 and 5d 1 energy levels of Ce 3+ . The results are shown in Tables 1 and 2 for Ce 3+ at the 6H and 4F sites, respectively.…”

Section: Ab Initio Calculationsmentioning

confidence: 99%

“…For lanthanide ions in dielectric crystals, the nature of ion–lattice interactions and chemical coordination are considered mostly ionic. The mixing of ionic–covalent interactions was realized in many previous studies. − Theoretical methods for understanding the consequences of ionic–covalent coordination are available. − Recent progresses in quantum chemical calculations enable quantitative understanding of structural and electronic properties in terms of covalent and ionic interactions. , However, theoretical analysis of the experimental results on the electronic transitions of ions in ionic–covalent mixed coordinates remains challenging. In silicate oxyapatites, two metal ion sites of different levels of covalence provide an ideal system for comparative studies of the consequences of covalent interactions.…”

Section: Introductionmentioning

confidence: 99%

Ce–O Covalence in Silicate Oxyapatites and Its Influence on Luminescence Dynamics

Zhai

¹

,

Ning

²

,

Huang

³

et al. 2014

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Cerium substituting gadolinium in Ca2Gd8(SiO4)6O2 occupies two intrinsic sites of distinct coordination. The coexistence of an ionic bonding at a 4F site and an ionic–covalent mixed bonding at a 6H site in the same crystalline compound provides an ideal system for comparative studies of ion–ligand interactions. Experimentally, the spectroscopic properties and photoluminescence dynamics of this white-phosphor are investigated. An anomalous thermal quenching of the photoluminescence of Ce3+ at the 6H site is analyzed. Theoretically, ab initio calculations are conducted to reveal the distinctive properties of the Ce–O coordination at the two Ce3+ sites. The calculated eigenstates of Ce3+ at the 6H site suggest a weak Ce–O covalent bond formed between Ce3+ and one of the coordinated oxygen ions not bonded with Si4+. The electronic energy levels and frequencies of local vibrational modes are correlated with specific Ce–O pairs to provide a comparative understanding of the site-resolved experimental results. On the basis of the calculated results, we propose a model of charge transfer and vibronic coupling for interpretation of the anomalous thermal quenching of the Ce3+ luminescence. The combination of experimental and theoretical studies in the present work provides a comprehensive understanding of the spectroscopy and luminescence dynamics of Ce3+ in crystals of ionic–covalent coordination.

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Luminescence

Fouassier¹

2005

Encyclopedia of Inorganic Chemistry

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This chapter is devoted to the luminescence of inorganic compounds. Luminescence characteristics are strongly host‐dependent. This is illustrated by various examples of the influence of covalency, crystal field, phonon energies, and structural features. The chapter is organized as follows. Section 2 describes the fundamentals of luminescence: probability of electronic transitions, shape of emission bands, quantum efficiency, energy transfer, and factors governing the position of the emitting level (nephelauxetic effect and crystal field splitting). Section 3 reviews the main families of luminescent ions: transition metal ions, lanthanide ions, and s 2 ions. The various types of electronic transitions responsible for the luminescence of transition and lanthanide ions are presented: nd → nd, (n + 1)s → nd, and charge transfer (CT) transitions for the former, 4f → 4f, 5d → 4f, and CT transitions for the latter. Data are given on the luminescence wavelength range, excited‐state lifetimes, thermal stability, and concentration quenching. Section 4 deals with donor‐acceptor transitions in ZnS. Section 5 presents the luminescence mechanisms for excitation through the host lattice. Vacuum ultraviolet (VUV), electron beam, X‐ray, and γ‐ray excitation are considered. The most efficient luminescent materials are given for the various types of excitation. Section 6 deals with electroluminescent materials.

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Luminescence

Fouassier

¹

2005

Encyclopedia of Inorganic and Bioinorganic Chemistry

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This chapter is devoted to the luminescence of inorganic compounds. Luminescence characteristics are strongly host‐dependent. This is illustrated by various examples of the influence of covalency, crystal field, phonon energies, and structural features. The chapter is organized as follows. Section 2 describes the fundamentals of luminescence: probability of electronic transitions, shape of emission bands, quantum efficiency, energy transfer, and factors governing the position of the emitting level (nephelauxetic effect and crystal field splitting). Section 3 reviews the main families of luminescent ions: transition metal ions, lanthanide ions, and s 2 ions. The various types of electronic transitions responsible for the luminescence of transition and lanthanide ions are presented: nd → nd, (n + 1)s → nd, and charge transfer (CT) transitions for the former, 4f → 4f, 5d → 4f, and CT transitions for the latter. Data are given on the luminescence wavelength range, excited‐state lifetimes, thermal stability, and concentration quenching. Section 4 deals with donor‐acceptor transitions in ZnS. Section 5 presents the luminescence mechanisms for excitation through the host lattice. Vacuum ultraviolet (VUV), electron beam, X‐ray, and γ‐ray excitation are considered. The most efficient luminescent materials are given for the various types of excitation. Section 6 deals with electroluminescent materials.

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Partly filled shells constituting anti-bonding orbitals with higher ionization energy than their bonding counterparts

Cited by 49 publications

References 107 publications

Ce–O Covalence in Silicate Oxyapatites and Its Influence on Luminescence Dynamics

Ce–O Covalence in Silicate Oxyapatites and Its Influence on Luminescence Dynamics

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