Potential well

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

Enhancement of electron-hole exchange interaction in CdSe nanocrystals: A quantum confinement effect

Abstract: Photoluminescence of CdSe nanocrystals in a glass matrix was investigated at low temperature with size-selective excitation. The emission spectrum consists of a line a few meV below the excitation laser energy (denoted the F line) and a two-phonon replica superimposed on a broadband. The energy difference between the excitation energy and the F-line position increases with decreasing nanocrystal size. From the analysis of the time behavior of the luminescence and the degree of linear polarization, we attribute the F line to the recombination of the optically forbidden A exciton. Radiation recombination is made possible through a phonon-assisted virtual transition to the confined B-exciton state. The experimental degree of linear polarization is in good agreement with the theoretical calculations. The value of the electron-hole exchange energy obtained from the energy separation between the excitation energy and the F line is much larger than the bulk value and reaches 24 meV in 30-\AA{}-diam. nanocrystals. The size dependence of the exchange energy is in good agreement with the theoretical prediction in the limit of small nanocrystals. \textcopyright{} 1996 The American Physical Society.

Optical properties of confined polaronic excitons in spherical ionic quantum dots

Abstract: We report the results of a variational calculation of the energy and the oscillator strength of the exciton ground state in a spherical ionic quantum dot as a function of radius, assuming infinite potential barriers. The strong interaction of the exciton with optical phonons is taken into account by using an effective potential between the electron and the hole as derived by Pollmann and B\"uttner. The values of the exciton ground-state energies calculated using this effective potential are compared with the results of a recent calculation that treats the exciton interaction with confined and interface phonons independently, and excellent agreement is found. Comparisons with two simpler models of excitons reveal that the high degree of confinement in small quantum dots suppresses polaronic corrections in exciton properties. The reduction of the electron-hole correlation in small quantum dots is observed in the behavior of oscillator strength, which becomes less dependent on the form of the effective interaction as the dot size is reduced. A proper definition of exciton transition energy in ionic materials is pointed out, where self-energy renormalization effects are important. The results of our calculation are presented for quantum dots of some ionic materials such as CdSe, GaN, ZnO, and CuCl.

Size dependence of photoluminescence and resonant Raman scattering from ZnO quantum dots

Abstract: ZnO quantum dots (QDs) of controlled sizes have been fabricated by a simple sol-gel method. The blueshift of room-temperature photoluminescence measurement from free exciton transition are observed decreasing with the QD size that is ascribed to the quantum confinement effect. From the resonant Raman scattering, the coupling strength between electron and longitudinal optical phonon, deduced from the ratio of the second- to the first-order Raman scattering intensity, diminishes with reducing the ZnO QD diameter. The size dependence of electron-phonon coupling is principally a result of the Frohlich interaction.

Triplet Energy Transfer from CsPbBr3 Nanocrystals Enabled by Quantum Confinement

Abstract: The spectral properties of lead halide perovskite nanocrystals (NCs) can be engineered by tuning either their sizes via the quantum confinement effect or their compositions using anion and/or cation exchange. To date, the latter is more frequently adopted, primarily because of the ease of ion exchange for lead halide perovskites, making the quantum confinement effect seemingly redundant for perovskite NCs. Here we report that quantum confinement is required for triplet energy transfer (TET) from perovskite NCs to polycyclic aromatic hydrocarbons (PAHs). Static and transient spectroscopy measurements on CsPbBr3 NC-pyrene hybrids showed that efficient TET occurred only for small-sized, quantum-confined CsPbBr3 NCs. The influences of the size-dependent driving force and spectral overlap on the TET rate were found to be negligible. Instead, the TET rate scaled linearly with carrier probability density at the NC surface, consistent with a Dexter-type TET mechanism requiring wave function exchange between the NC donors and pyrene acceptors. Efficient TET funnels the excitation energy generated in strongly light-absorbing perovskite NCs into long-lived triplets in PAHs, which may find broad applications such as photon upconversion and photoredox catalysis.

Growth of 2D GaN Single Crystals on Liquid Metals

Abstract: Two-dimensional (2D) gallium nitride (GaN) has been highly anticipated because its quantum confinement effect enables desirable deep-ultraviolet emission, excitonic effect and electronic transport properties. However, the currently obtained 2D GaN can only exist as intercalated layers of atomically thin quantum wells or nanometer-scale islands, limiting further exploration of its intrinsic characteristics. Here, we report, for the first time, the growth of micrometer-sized 2D GaN single crystals on liquid metals via a surface-confined nitridation reaction and demonstrate that the 2D GaN shows uniformly incremental lattice, unique phonon modes, blue-shifted photoluminescence emission and improved internal quantum efficiency, providing direct evidence to the previous theoretical predictions. The as-grown 2D GaN exhibits an electronic mobility of 160 cm2·V–1·s–1. These findings pave the way to potential optoelectronic applications of 2D GaN single crystals.