Quantum-size-induced electronic transitions in quantum dots: Indirect band-gap GaAs

2008 ◽  
Vol 78 (3) ◽  
Author(s):  
Jun-Wei Luo ◽  
Alberto Franceschetti ◽  
Alex Zunger
Keyword(s):  
Quantum Dots ◽  
Band Gap ◽  
Electronic Transitions ◽  
Quantum Size ◽  
Indirect Band Gap

Phenomenological Modeling of Confined Phonon States in TMD Quantum Dots

MRS Advances ◽  
2018 ◽  
Vol 3 (6-7) ◽  
pp. 339-344 ◽  
Author(s):  
Lu Fang ◽  
Tamia Willliam ◽  
Kofi W. Adu ◽  
Mauricio Terrones
Keyword(s):  
Quantum Dots ◽  
Size Effect ◽  
Band Gap ◽  
Bulk Material ◽  
Single Layer ◽  
Interlayer Coupling ◽  
Quantum Size Effect ◽  
Quantum Size ◽  
Indirect Band Gap ◽  
Band Gap Tuning

ABSTRACTSeveral reports have shown band-gap tuning in TMDs, from indirect band gap in the bulk material to a direct gap in single layer due to the absence of interlayer coupling. This unique property stems from the modified electronic states. The phononic properties are extremely modified as well, due to layered effect and quantum size effect. There are several reports on layered effect; however, reports on the confined phonon states in these structures are limited. Thus, we present a preliminary studies of the confined phonon states in TMDs (WS2 and MoS2) quantum dots, and elucidate on the evolution of the phonon lineshape with diameter using a phenomenological model with an envelop function that truncates the phonon wave at the surface of the quantum dot. Furthermore, we delineate the layered effect from the quantum size effect in the phonon lineshape of WS2 and MoS2.

Facile one-step sonochemical synthesis of AgCl quantum dots with enhanced photocatalytic activity and its size effects

2020 ◽  
Vol 13 (06) ◽  
pp. 2051036
Author(s):  
Junjie Zhang ◽  
Hujiabudula Maimaitizi ◽  
Tao Zhang ◽  
Yalkunjan Tursun ◽  
Dilinuer Talifu ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Photocatalytic Activity ◽  
Band Gap ◽  
Size Effects ◽  
Ultrasonic Method ◽  
Energy Levels ◽  
Average Diameter ◽  
Light Illumination ◽  
Quantum Size ◽  
One Step

In this work, a facile ultrasonic method for the fabrication of AgCl quantum dots (AgCl QDs) with an average diameter of about 2.5[Formula: see text]nm was reported for the first time. The material was analyzed by various techniques. In addition, effects of material’s size on its photocatalytic activities were studied. Results suggested that the AgCl QDs exhibited excellent photocatalytic activity to degrade Rhodamine B (RhB) and tetracycline (TC) under visible light illumination, and the degradation rate of RhB (TC) had reached up to 96.6% (72.2%) in 20 min, which was higher than that of AgCl nanoparticles (23[Formula: see text]nm) and AgCl nanospheres (114[Formula: see text]nm), respectively. Besides, the band gap of the material was increased when the size of material decreased from 23[Formula: see text]nm to 2.5[Formula: see text]nm. The significantly improved photocatalytic performance and increased band gap of AgCl QDs were mainly related to the quantum size effects of AgCl, which results in the more electron fluctuation in quantized energy levels and the lower recombination of electrons and holes.

Phonon-Assisted Indirect Transitions in Cadmium Sulfate Crystals

1978 ◽  
Vol 33 (7) ◽  
pp. 815-821
Author(s):  
C. S. Sunandana ◽  
C. Ramasastry
Keyword(s):  
Raman Spectrum ◽  
Band Gap ◽  
Photon Energy ◽  
Power Law ◽  
Absorption Edge ◽  
Fundamental Absorption Edge ◽  
Electronic Transitions ◽  
Cadmium Sulfate ◽  
Laser Raman ◽  
Indirect Band Gap

The fundamental absorption edge of “suprapur” cadmium sulphate (3CdSO4 · 8H2O) crystal occurs in the region below 200 nm. The power-law dependence of the optical density on photon energy suggests indirect electronic transitions made possible by the emission or absorption of 0.067 eV phonons. The indirect band gap (Eg′) at 300 K is 6.09 eV. The phonon energy of 0.067 eV is found to arise from one of the Raman-active modes (E ) of the sulphate ion. The band edge is found to shift monotonically towards higher energies at a rate of - 2.3 meV per K between 300 and 77 K. The laser Raman spectrum of the 3CdSO4 · 8H2O is also reported.

scholarly journals Optical orientation and alignment of excitons in direct and indirect band gap (In,Al)As/AlAs quantum dots with type-I band alignment

2019 ◽  
Vol 99 (19) ◽  
Author(s):  
J. Rautert ◽  
T. S. Shamirzaev ◽  
S. V. Nekrasov ◽  
D. R. Yakovlev ◽  
P. Klenovský ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Band Gap ◽  
Band Alignment ◽  
Type I ◽  
Optical Orientation ◽  
Indirect Band Gap

Luminescence of Direct and Indirect Gap Quantum Semiconductor Crystallites

1992 ◽  
Vol 272 ◽  
Author(s):  
L. E. Brus
Keyword(s):  
Quantum Dots ◽  
Size Effect ◽  
Band Gap ◽  
Three Dimensional ◽  
Electronic States ◽  
Quantum Size Effect ◽  
Excited Electronic States ◽  
Quantum Size ◽  
Quantum Semiconductor ◽  
Bulk Band

Semiconductor crystallites (“quantum dots”) small with respect to the bulk exciton Bohr diameter show a three dimensional electronic quantum size effect. Their internal excited electronic states are discrete and shifted to higher energy than the bulk band gap[1,2].

scholarly journals Spin-flip Raman scattering of theΓ−Xmixed exciton in indirect band gap (In,Al)As/AlAs quantum dots

2014 ◽  
Vol 90 (12) ◽  
Author(s):  
J. Debus ◽  
T. S. Shamirzaev ◽  
D. Dunker ◽  
V. F. Sapega ◽  
E. L. Ivchenko ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Raman Scattering ◽  
Band Gap ◽  
Spin Flip ◽  
Indirect Band Gap

Artificial Atoms of Silicon

1999 ◽  
Vol 582 ◽  
Author(s):  
Justin D. Holmes ◽  
Kirk J. Ziegler ◽  
Keith P. Johnston ◽  
R. Chris Doty ◽  
Brian A. Korgel
Keyword(s):  
Quantum Yield ◽  
Band Gap ◽  
Silicon Nanocrystals ◽  
Room Temperature ◽  
Band Edge ◽  
Electronic Transitions ◽  
Photoluminescence Excitation ◽  
Blue Band ◽  
Artificial Atoms ◽  
Indirect Band Gap

ABSTRACTSize-monodisperse, stable 15 Å diameter silicon nanocrystals were synthesized in significant quantities using supercritical octanol as a capping ligand. The silicon nanocrystals exhibit an indirect band gap with discrete electronic transitions in the absorbance and photoluminescence excitation (PLE) spectra. The octanol-capped clusters show efficient blue band-edge photoemission with a luminescence quantum yield of 23 % at room temperature.

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