CdSe-ZnS Core-Shell Quantum Dots: Surface Plasmons Effect and Optical Spectra

Abstract

<p>Absorption and photoluminescence (PL) spectra of a colloidal CdSe-ZnS core-shell quantum dots (QDs) were measured within the strong confinement regime. The QDs were casted on half-coated quartz substrates with 50 nm of gold and prepared for studying the surface plasmons effect. The samples were optically arranged and pumped by different wavelengths, and the PL spectra were detected. Excitation with a wavelength of 400 nm reveals a structure fluorescence spectrum which consists of five distinct bands. These bands are more intense and resolved than the corresponding traditional weak absorption bands. They were detected for the first time and assigned according to the theoretical predictions of excitons in a spherical potential with Coulomb interactions and valence bands mixing. A scheme based on multiple exciton generation (MEG) for the appearance of the fluorescence bands was proposed. This scheme was confirmed by the recent theoretical prediction using the state-of-the art time domain <em>ab initio </em>density functional theory and the atomistic pseudopotential calculations. The detected surface plasmons effect in QDs enhances the intensity of the fluorescence bands. This surface plasmons effect facilitated the appearance of these mentioned bands in more intensive features than the corresponding traditional weak absorption bands. Furthermore, the reduction in the measured lifetime of the first excited electronic state from 20 ns for the QDs deposited directly on the quartz substrate to 7 ns for the QDs casted on the gold film, gives a further evidence of the surface plasmons effect in the (PL) of the CdSe-ZnS QDs.</p><span style="font-family: Times New Roman; font-size: small;"> </span><p class="MsoNormal" style="margin: 0cm 0cm 10pt; text-align: justify; line-height: 150%; unicode-bidi: embed; direction: ltr;"><span style="line-height: 150%; font-family: "Times New Roman","serif"; font-size: 12pt; mso-ascii-theme-font: major-bidi; mso-hansi-theme-font: major-bidi; mso-bidi-theme-font: major-bidi;"></span></p><span style="font-family: Times New Roman; font-size: small;"> </span

The Fabrication of the Infrared CdSe Doped With Cu Photodetector

“…However, this tuning spectrum was detected by using a surface Plasmon's technique. Five distinguishable transitions were detected by the absorption and fluorescence spectra of the CdSe quantum dots (Mohammed, 2013). The populations of these levels were explained by the multiple exciton generation (MEG), in full agreement with the theoretical predictions.…”

“…A) Energy levels involved in the absorption of CdSe:Cu film B) Energy Levels involved in the absorption and fluorescence of CdSe-ZnS core-shell quantum dots (Mohammed, 2013) www.ccsenet.org/apr Applied Physics Research Vol. 8, No.…”