Potential well

About: Potential well is a research topic. Over the lifetime, 1430 publications have been published within this topic receiving 30812 citations.

Surface passivation dependent photoluminescence from silicon quantum dot phosphors.

Abstract: We demonstrate wavelength-tunable, air-stable and nontoxic phosphor materials based on silicon quantum dots (SiQDs). The phosphors, which are composed of micrometer-size silicon particles with attached SiQDs, are synthesized by an electrochemical etching method under ambient conditions. The photoluminescence (PL) peak wavelength can be controlled by the SiQD size due to quantum confinement effect, as well as the surface passivation chemistry of SiQDs. The red-emitting phosphors have PL quantum yield equal to 17%. The SiQD-phosphors can be embedded in polymers and efficiently excited by 405 nm light-emitting diodes for potential general lighting applications.

Cathodoluminescence in single and multiwall WS2 nanotubes: Evidence for quantum confinement and strain effect

Abstract: For nanoparticles with sub-10 nm diameter, the electronic bandgap becomes size dependent due to quantum confinement; this, in turn, affects their electro-optical properties. Thereby, MoS2 and WS2 monolayers acquire luminescent capability, due to the confinement-induced indirect-to-direct bandgap transition. Rolling up of individual layers results in single wall inorganic nanotubes (SWINTs). Up to the present study, their luminescence properties were expected to be auspicious but were limited to theoretical investigations only, due to the scarcity of SWINTs and the difficulties in handling them. By optimizing the conditions in the plasma reactor, relatively high yields of WS2 SWINTs 3–7 nm in diameter were obtained in this work, compared to previous reports. A correlative approach, transmission electron microscopy coupled with a scanning electron microscope, was adapted to overcome handling obstacles and for testing individual nanotubes by low-temperature cathodoluminescence. Clear cathodoluminescence spectra were obtained from WS2-SWINTs and compared with those of WS2 multiwall nanotubes and the corresponding bulk material. Uniquely, the optical properties of INTs acquired from cathodoluminescence were governed by the opposite impact from quantum size effect and strain in the bent triple S-W-S layers. The experimental findings were confirmed by the Density Functional and Time-Dependent Density Functional theoretical modeling of monolayer and bilayer nanotubes of different chiralities and diameters. This study provides experimental evidence of the quantum confinement effect in WS2 SWINTs akin to WS2 monolayer. The ability to tune the electronic structure with morphology or number of layers may be exploited toward photoelectrochemical water splitting with WS2 catalysts, devising field effect transistors, photodetectors, and so on.

Ultrafast nonlinear gain dynamics in semiconductor nanocrystals

Abstract: II - VI semiconductor (CdS, CdSe) nanocrystals with an average size of approximately one bulk exciton Bohr radius are embedded in a glass matrix. Due to the quantum confinement effect, they act as a quasi zero-dimensional system (quantum dots). Under strong nanosecond and femtosecond optical excitation, these quantum dots exhibit optical amplification (gain). We investigate the ultrashort gain dynamics of the strongly confined CdSe quantum dots by femtosecond pump-probe spectroscopy. From multiple-beam pump-probe measurements, we conclude that the gain mechanism is governed by biexciton to exciton transitions. Femtosecond dephasing measurements reveal a constant scattering rate across the gain region and confirm the two-electron-hole pair gain model. Nanosecond pump-probe measurements on CdS quantum dots in sol-gel glasses show optical gain up to room temperature. In all cases, the gain region is broad and stretches below the fundamental absorption of the nanocrystals. The reason is the multitude...