Electronic and Optical Properties of Silicon Nanocrystals: Structural Effects

2003 ◽  
Vol 770 ◽  
Author(s):  
E. Degoli ◽  
S. Ossicini ◽  
M. Luppi ◽  
E. Luppi ◽  
R. Magri ◽  
...  
Keyword(s):  
Optical Properties ◽  
Excited State ◽  
Silicon Nanocrystals ◽  
Structural Model ◽  
Stokes Shift ◽  
Optical Gain ◽  
Structural Effects ◽  
Electronic And Optical Properties ◽  
Cluster Dimension ◽  
Pseudopotential Calculations

AbstractThe aim of this work is to investigate the structural, electronic and optical properties of hydrogenated Si nanoclusters (H-Si-nc) in their ground and excited state configurations. Structural relaxations have been fully taken into account in all cases through total energy pseudopotential calculations. Recent results about ab-initio calculations of Stokes shift as a function of the cluster dimension and of optical gain will be presented here. A structural model that can be linked to the four level scheme recently invoked to explain the experimental outcomes relative to the observed optical gain in Si-nc embedded in a SiO2 matrix will be suggested too.

Doping in silicon nanocrystals: An ab initio study of the structural, electronic and optical properties

2006 ◽  
Vol 121 (2) ◽  
pp. 335-339 ◽  
Author(s):  
Federico Iori ◽  
Elena Degoli ◽  
Eleonora Luppi ◽  
Rita Magri ◽  
Ivan Marri ◽  
...  
Keyword(s):  
Optical Properties ◽  
Ab Initio ◽  
Silicon Nanocrystals ◽  
Ab Initio Study ◽  
Electronic And Optical Properties

First-Principles Study of Silicon Nanocrystals: Structural and Electronic Properties, Absorption, Emission, and Doping

2008 ◽  
Vol 8 (2) ◽  
pp. 479-492 ◽  
Author(s):  
Stefano Ossicini ◽  
O. Bisi ◽  
Elena Degoli ◽  
I. Marri ◽  
Federico Iori ◽  
...  
Keyword(s):  
Optical Properties ◽  
Silicon Nanocrystals ◽  
Density Functional ◽  
Stokes Shift ◽  
Emission Spectra ◽  
Visible Range ◽  
Hydrogenated Silicon ◽  
Absorption And Emission ◽  
Co Doping ◽  
Electron Hole Pair

Total energy calculations within the Density Functional Theory have been carried out in order to investigate the structural, electronic, and optical properties of un-doped and doped silicon nano-structures of different size and different surface terminations. In particular the effects induced by the creation of an electron-hole pair on the properties of hydrogenated silicon nanoclusters as a function of dimension are discussed in detail showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure by an electronic excitation of the cluster is analyzed and considered in the evaluation of the Stokes shift between absorption and emission energies. Besides we show how many-body effects crucially modify the absorption and emission spectra of the silicon nanocrystals. Starting from the hydrogenated clusters, different Si/O bonding at the cluster surface have been considered. We found that the presence of a Si—O—Si bridge bond originates significative excitonic luminescence features in the near-visible range. Concerning the doping, we consider B and P single- and co-doped Si nanoclusters. The neutral impurities formation energies are calculated and their dependence on the impurity position within the nanocrystal is discussed. In the case of co-doping the formation energy is strongly reduced, favoring this process with respect to the single doping. Moreover the band gap and the optical threshold are clearly red-shifted with respect to that of the pure crystals showing the possibility of an impurity based engineering of the absorption and luminescence properties of Si nanocrystals.

Electronic Structure of Divalent Defects in Tetrahedrally Bonded Amorphous Materials

1986 ◽  
Vol 70 ◽  
Author(s):  
S. Y. Lin ◽  
G. Lucovsky ◽  
S. Guha ◽  
J. S. Payson
Keyword(s):  
Optical Properties ◽  
Amorphous Materials ◽  
Structural Model ◽  
Experimental Studies ◽  
Bethe Lattice ◽  
Conduction Band Edge ◽  
Dangling Bond ◽  
Dangling Bonds ◽  
Electronic And Optical Properties ◽  
Tetrahedrally Bonded

ABSTRACTThis paper describes a calculation of twofold-coordinated (or divalent) intrinsic bonding defects in a-SiSn:H alloy films. The motivation for this study comes from experimental studies of the electronic and optical properties of a- Si, Sn:H alloys which indicate dramatic changes in the electronic and photoelectronic properties for small concentrations of Sn (approximately 1–2 at. %). We have used a cluster Bethe lattice structural model and an empirical tight-binding Hamiltonian to investigate the electronic properties of tetrahedrally bonded Sn atoms and neutral Sn defect centers (T2o and T3o) and in an a-Si host. We find that: (C) fourfoldcoordinated Sn atoms simply promote a reduction in the optical bandgap, with the energy gap disappearing for Sn concentrations of about 20 to 30 at. %; (2) neutral dangling bonds (T2o) or threefold-coordinated Sn atoms generate a localized state in the gap that is iower in energy than the corresponding neutral Si atom dangling bond; and (3) divalent (T2o) or twofold-coordinated Sn atoms give rise to two states in the gap, an occupied state that is lower in energy that either the Sn or Si dangling bond, and an empty state that is just below the conduction band edge. We show that the electronic and optical properties of the a-SiSn:H alloys can be understood in terms of a model in which there are relatively high densities of unhydrogenated Sn divalent sites and/or Sn dangling bonds.

scholarly journals Understanding the Photocatalytic Properties of Pt/CeO x /TiO 2 : Structural Effects on Electronic and Optical Properties

ChemPhysChem ◽  
2019 ◽  
Vol 20 (12) ◽  
pp. 1624-1629 ◽  
Author(s):  
J. J. Plata ◽  
E. R. Remesal ◽  
Jesús Graciani ◽  
A. M. Márquez ◽  
J. A. Rodríguez ◽  
...  
Keyword(s):  
Optical Properties ◽  
Photocatalytic Properties ◽  
Structural Effects ◽  
Electronic And Optical Properties

scholarly journals Temperature-Dependence of Solvent-Induced Stokes Shift and Fluorescence Tunability in Carbon Nanodots

2019 ◽  
Vol 5 (2) ◽  
pp. 20 ◽  
Author(s):  
Sciortino ◽  
Cannas ◽  
Messina
Keyword(s):  
Optical Properties ◽  
Excited State ◽  
Low Temperature ◽  
Carbon Dots ◽  
Emission Band ◽  
Stokes Shift ◽  
Carbon Nanodots ◽  
Emission Mechanism ◽  
Role Of Solvent

We carried out a cryogenic investigation on the optical properties of carbon dots, aiming to better understand their emission mechanism and the role of the solvent. The solvatochromic Stokes shift is quantified by a low temperature approach which allows freezing of the photo-excited state of carbon dots, preventing any solvation relaxation. Moreover, the reduction in temperature helps to identify the dynamical inhomogeneous contribution to the broadening of the emission band; therefore, disentangling the role of solvent from other types of broadening, such as the homogeneous and the static inhomogeneous contributions.

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