Optical electron transfer between metal ions and its consequences
01 Jan 1991-pp 153-187
TL;DR: In this paper, a survey of metal-to-metal charge transfer transitions is presented, focusing on species of interest originate from non-molecular and molecular solids and from solutions.
Abstract: This paper surveys several aspects of metal-to-metal charge-transfer transitions. Species of interest originate from non-molecular and molecular solids and from solutions. The parallel in the different approaches is stressed. In addition to the spectroscopy of these transitions, their influence or role in other phenomena is also discussed.
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TL;DR: In this paper, structural and luminescence properties of fluoride and oxyfluoride phosphors were described and compared with a (Sr,Ca)3(Al,Si)O4(F,O):Ce3+ yellow-green phosphor and a K2TiF6:Mn4+ red phosphor.
Abstract: LED lamps using phosphor downconversion can be designed to replace incandescent or halogen sources with a “warm-white” correlated color temperature (CCT) of 2700−3200 K and a color rendering index (CRI) greater than 90. However, these lamps have efficacies of ∼70% of standard “cool-white” LED packages (CCT = 4500−6000 K; CRI = 75−80). In this report, we describe structural and luminescence properties of fluoride and oxyfluoride phosphors, specifically a (Sr,Ca)3(Al,Si)O4(F,O):Ce3+ yellow-green phosphor and a K2TiF6:Mn4+ red phosphor, that can reduce this gap and therefore meet the spectral and efficiency requirements for high-efficacy LED lighting. LED lamps with a warm-white color temperature (3088 K), high CRI (90), and an efficacy of ∼82 lm/W are demonstrated using these phosphors. This efficacy is ∼85% of comparable cool-white lamps using typical Y3Al5O12:Ce3+-based phosphors, significantly reducing the efficacy gap between warm-white and cool-white LED lamps that use phosphor downconversion.
250 citations
TL;DR: It is shown, through a critical review of the archival literature, that this model provides new insights on the assignment of the luminescence spectra and the related interpretation of the spectroscopic behaviors.
Abstract: A model is introduced to predict the energy of metal-to-metal charge-transfer transitions in oxide compounds containing Bi3+ ions and d0 or d10 metals (Mn+). The model takes into account the structural characteristics of the host lattices, the anion relaxation resulting from Bi3+ doping, and the electronegativities and coordination numbers of the Bi3+ and Mn+ ions in the compounds. It is shown, through a critical review of the archival literature, that this model provides new insights on the assignment of the luminescence spectra and the related interpretation of the spectroscopic behaviors.
228 citations
TL;DR: In this article, the performance of cobalt and cobalt-phosphorus catalysts in the presence of octahedral Co 2+ ions was investigated in the context of ethane ODH.
223 citations
TL;DR: In this article, a Pt-cocatalyst-free, CdS-layered titanate nanohybrids were shown to have much higher photocatalytic activity for H2 production than the precursors, which is due to the increased lifetime of the electrons and holes, the decrease of the bandgap energy, and the expansion of the surface area upon hybridization.
Abstract: Highly efficient, visible-light-induced H2 generation can be achieved without the help of a Pt cocatalyst by new hybrid photocatalysts, in which CdS quantum dots (QDs) (particle size ≈2.5 nm) are incorporated in the porous assembly of sub-nanometer-thick layered titanate nanosheets. Due to the very-limited crystal dimension of component semiconductors, the electronic structure of CdS QDs is strongly coupled with that of the layered titanate nanosheets, leading to an efficient electron transfer between them and the enhancement of the CdS photostability. As a consequence of the promoted electron transfer, the photoluminescence of CdS QDs is nearly quenched after hybridization, indicating the almost-suppression of electron-hole recombination. These Pt-cocatalyst-free, CdS-layered titanate nanohybrids show much-higher photocatalytic activity for H2 production than the precursor CdS QDs and layered titanate, which is due to the increased lifetime of the electrons and holes, the decrease of the bandgap energy, and the expansion of the surface area upon hybridization. The observed photocatalytic efficiency of these Pt-free hybrids (≈1.0 mmol g−1 h−1) is much greater than reported values of other Pt-free CdS-TiO2 systems. This finding highlights the validity of 2D semiconductor nanosheets as effective building blocks for exploring efficient visible-light-active photocatalysts for H2 production.
183 citations
TL;DR: MoO42/WO42-intercalated layered double hydroxide (LDH) was prepared by taking nitrate intercalated Zn/Y LDH by the ion exchange method as discussed by the authors.
Abstract: MoO42–/WO42– intercalated layered double hydroxide (LDH) was prepared by taking nitrate intercalated Zn/Y LDH (Zn/Y/N) by the ion exchange method. The structure, morphology, texture, optical absorp...
155 citations
References
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TL;DR: In this article, the resonance theory of Forster, which involves only allowed transitions, is extended to include transfer by means of forbidden transitions which, it is concluded, are responsible for the transfer in all inorganic systems yet investigated.
Abstract: The term ``sensitized luminescence'' in crystalline phosphors refers to the phenomenon whereby an impurity (activator, or emitter) is enabled to luminesce upon the absorption of light in a different type of center (sensitizer, or absorber) and upon the subsequent radiationless transfer of energy from the sensitizer to the activator The resonance theory of Forster, which involves only allowed transitions, is extended to include transfer by means of forbidden transitions which, it is concluded, are responsible for the transfer in all inorganic systems yet investigated The transfer mechanisms of importance are, in order of decreasing strength, the overlapping of the electric dipole fields of the sensitizer and the activator, the overlapping of the dipole field of the sensitizer with the quadrupole field of the activator, and exchange effects These mechanisms will give rise to ``sensitization'' of about 103−104, 102, and 30 lattice sites surrounding each sensitizer in typical systems The dependence of transfer efficiency upon sensitizer and activator concentrations and on temperature are discussed Application is made of the theory to experimental results on inorganic phosphors, and further experiments are suggested
7,635 citations
TL;DR: In this article, a review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation, and a number of references cite that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures.
Abstract: Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.
2,208 citations
TL;DR: A new theory is presented for describing band gaps and electronic structures of transition-metal compounds and both the metallic sulfides and insulating oxides and halides occur in a quite natural manner.
Abstract: A new theory is presented for describing band gaps and electronic structures of transition-metal compounds. A theoretical phase diagram is presented in which both the metallic sulfides and insulating oxides and halides occur in a quite natural manner.
2,190 citations