The Interband Transition Region: Crystalline Materials

Adachi, Sadao

doi:10.1007/978-1-4615-5241-3_3

Cited by 2 publications

(2 citation statements)

References 75 publications

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“…Quantitative examination of the electronic structures of the POTs was first performed by calculation of the HOMO–LUMO transitions (Figure S5). The direct transitions and indirect transitions are obtained by extrapolation of the (α h ν ) 2 and (α h ν ) 1/2 (α, absorption coefficient; h , Planck’s constant; ν, frequency) plots to the horizontal axis ( h ν ), and the values are listed in Table . , These values are energies needed for excitation of an electron from the HOMO (valence band) to the LUMO (conduction band). The transitions from the valence band maximum (VBM) to the conduction band minimum (CBM) are indirect transitions (obtained from the (α h ν ) 1/2 vs h ν plot), corresponding to lower extinction coefficients, and determine the minimum energy necessary for optical excitation.…”

Section: Resultssupporting

confidence: 88%

Effects of Substitutional Dopants on the Photoresponse of a Polyoxotitanate Cluster

Zhan

Zhang

et al. 2016

Inorg. Chem.

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In this paper, using a simple method, 17 isostructural polyoxotitanates (POTs) were synthesized, including the pristine [Ti12O16(O(i)Pr)16], the monodefected [Ti11O13(O(i)Pr)18], and the heterometal-doped [Ti11O14(O(i)Pr)17(ML)] (M = Mg, Ca, Zn, Cd, Co, or Ni; L = Cl, Br, I, or NO3). The electronic structures of these POTs were determined by UV-vis spectroscopy and DFT calculations. Upon UV irradiation of the POTs, electron spin resonance showed the formation of Ti(III) under anaerobic conditions and superoxide (O2(•-)) in the presence of O2. The photoactivities of the POTs were then probed with Ti(III) production and short-circuit photocurrent experiments. The photophysical processes were studied using steady-state and transient photoluminescence. The results show that within the very similar structures, the deexcitation processes of the photoexcited POTs can be greatly affected by the dopants, which result in enhanced or decreased photoactivities. Co and Ni doping enhances the absorption of the visible light accompanied by serious loss of UV photoactivities. On the other hand, a Ti vacancy (in [Ti11O13(O(i)Pr)18]) does not reduce the band gap of a POT but improves the UV photoactivities by serving as surface reaction site. The POTs were then used as molecular models of titanium oxide nanoparticles to understand some important issues relevant to doped titanate, i.e., coordination environment of the dopant metal, electronic structure, photoactivities, and photophysical processes. Our present findings suggest that for solar energy harvesting applications of titanium oxides like photocatalysis and solar cells substitution of titanium atoms by transition metal ions (like Co and Ni) to extend the absorption edges may not be an efficient way, while loading of Ti vacancies is very effective.

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Section: Resultssupporting

confidence: 88%

Effects of Substitutional Dopants on the Photoresponse of a Polyoxotitanate Cluster

Zhan

Zhang

et al. 2016

Inorg. Chem.

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“…(iii) the external medium has a refractive index of 1.5, like epoxy; (iv) DBRs are phase matched with the cavity: λ DBR = λ FP = Ln, where λ DBR is the central wavelength of the DBRs and n = 3.4 (at 880 nm), is the refractive index of the cavity medium; (v) Al x Ga 1−x As refractive indexes are taken from reference [33]; (vi) absorption into the QWs is fixed at 0.3% per QW and per pass (3000 cm −1 for 10 nm thick QWs); (vii) free carrier absorption due to doping is set to α dop = 10 cm −1 for all layers [34,35].…”

Section: Optical Designmentioning

confidence: 99%

Microcavity light emitting diodes as efficient planar light emitters for telecommunication applications

Ochoa

Houdré

Ilegems

et al. 2002

Comptes Rendus. Physique

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Light emitting diodes (LEDs) can be coupled to optical fibers and used in telecommunication applications. Compared to laser diodes, the coupling is usually small, due to the isotropic emission of the source, combined with the large refractive index difference between the semiconductor and the outside medium. However, it is possible to greatly enhance the optical extraction of a planar LED by placing the source inside a microcavity which optical thickness is close to the wavelength of the emitted light. Some elementary design rules of a microcavity light emitting diode (MCLED) are explained here, and are illustrated on a real GaAs/Al x Ga 1−x As device emitting at 880 nm. The surface external quantum efficiency of this MCLED reaches 14% into air and 20.6% with an encapsulation into an epoxy lens. These values are about 10 times larger than for a usual LED and are in good agreement with theoretical values, calculated with a plane waves model. To cite this article: D. Ochoa et al., C. R. Physique 3 (2002) 3-14.  2002 Académie des sciences/Éditions scientifiques et médicales Elsevier SAS light emitting diode / microcavity / brightness / Fabry-Pérot / semiconductors La diode électroluminescente à microcavité : un émetteur de lumière planaire efficace pour des applications en télécommunications Résumé Les diodes électroluminescentes (LEDs) peuvent être couplées à des fibres optiques et utilisées pour des applications en télécommunications. Ce couplage est généralement assez faible, en comparaison de celui qui est obtenu avec des diodes laser. Ceci est dû principalement à l'émission isotropique de la source, combinée à la grande différence d'indice de réfraction entre le semiconducteur et le milieu extérieur. Cependant, l'extraction optique d'une LED planaire peut être largement augmentée si la source est placée à l'intérieur d'une microcavité dont l'épaisseur est proche de la longueur d'onde de la lumière émise. Nous expliquons ici quelques règles fondamentales de conception d'une LED à microcavité (MCLED), et nous les illustrons avec l'exemple d'un composant réel en GaAs/Al x Ga 1−x As, émettant à 880 nm. Le rendement quantique externe de cette MCLED atteint 14% pour une emission dans l'air et 20,6% avec une encapsulation dans une lentille en époxy. Ces valeurs sont près de dix fois supérieures à celles d'une LED standard, et sont

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The Interband Transition Region: Crystalline Materials

Cited by 2 publications

References 75 publications

Effects of Substitutional Dopants on the Photoresponse of a Polyoxotitanate Cluster

Effects of Substitutional Dopants on the Photoresponse of a Polyoxotitanate Cluster

Microcavity light emitting diodes as efficient planar light emitters for telecommunication applications

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