49 research outputs found
Spatial localization of quantized states responsible for sharp optical transition in AlGaN/GaN superlattice
No full textAccurate Color Tuning of Firefly Chromophore by Modulation of Local Polarization Electrostatic Fields
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Spatial localization of quantized states responsible for sharp optical transition in AlGaN/GaN superlattice
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Coupled donor states in InP by Sn doping
No full textCoupled donor states induced by Sn doping into InP and their behaviors were studied by employing photoluminescence (PL) measurements and first-principles calculations. InP: Sn crystals were grown in the [100] orientation by a modified liquid-encapsulated vertical Bridgman technique. The PL data show a donor-acceptor recombination line and its phonon replica at 898 nm and 926 nm, respectively, and another recombination line around 800 nm, which uniquely appears at the top in high Sn concentration. The first-principles calculations for the InP:Sn system support these results by observing two separate donor levels below (D(Sn1)) and above (D(Sn2)) the bottom of the conduction band, which are responsible for the recombination lines. They deviate from the bottom of the conduction band with the increase of Sn concentration. A peak at 879 nm from the band-to-band transition could only be visible at room temperature. The PL mapping of this line shows the increase of Sn concentrations with the crystal growth, which helps to reduce the dislocation density and increase the lifetime of excess carriers
Kinetic behavior of nitrogen penetration into indium double layer improving the smoothness of InN film
No full textThe kinetic process of the formation of InN thin film was clarified via the investigation of the layer-by-layer deposition on (0001) surface, by first-principles calculations. Site selection and diffusion behavior of In and N adatoms revealed an extraordinary growth kinetics. The indium bilayer preferably deposits in the initial stage and then the N atoms come up and penetrate vertically through a specific channel into between this double layer, finally forming the tetrahedral coordination of InN. Following this kinetic process, alternative pulse supply of precursors was proposed for the InN film growing and smoothening, which can effectively improve the surface smoothness. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4728993
Full Color Modulation of Firefly Luciferase through Engineering with Unified Stark Effect
No full textInternational audienceThe firefly luciferase has been a unique marking tool used in various bioimaging techniques. Extensive color modulation is strongly required to meet special marking demands; however, intentional and accurate wavelength tuning has yet to be achieved. Here, we demonstrate that the color shift of the firefly chromophore (OxyLH2-1) by internal and external fields can be described as a unified Stark shift. Electrostatic microenvironmental effects on fluorescent spectroscopy are modeled in vacuo through effective electric fields by using time-dependent density functional theory. A complete visible fluorescence spectrum of firefly chromophore is depicted, which enables one to control the emission in a specific color. As an application, the widely observed pH-correlated color shift is proved to be associated with the local Stark field generated by the trace water–ions (vicinal hydronium and hydroxide ions) at active sites close to the OxyLH2-1
