Analyzing dark exciton and altering emission of cdse nanocrystalline quantum dots

Abstract

Colloidal nanocrystalline quantum dots (QDs) are promising semiconductor material for many advanced optical devices applications. QDs have broad absorption spectra and narrow emission spectra. Furthermore, QDs have high quantum efficiency and photo-stability, compared to organic dyes molecules. QDs have been applied in many applications, such as light emitting diodes, solar cells, biomarkers, etc. QDs are also good candidate for single photon source in ambient atmosphere. This application is visible for QDs because the QDs are the smallest synthetic particle in the world. The size of QDs is even smaller than Bohr radius; therefore, the confinement of electrons in the QDs is very strong. Thus, the recombination process at single QD results in very sharp emission peak. However, some drawbacks prevent the application of single QD to advanced optical devices, such as single photon source. Those drawbacks are photobleaching, photoblueing, and photoblinking. One must solve or manipulate optical properties of single QD for further applications. Meanwhile, the optical properties of ensemble of QDs are also very useful in many advanced optical devices. One characteristic of optical properties of QDs is that the emission of QDs isotropic. Sometimes, it is necessary to alter the QDs emission. The QDs emission could be guided, reflected, re-directed, etc. There are several useful optical devices to alter QDs emission, such as, optical waveguide, fiber optics, and photonic crystals. In this work, we would like to alter photoblinking of single QD emission and to modify ensemble QDs emission. Photoblinking property of single QD is altered by changing geometrical structure of QDs. The emission of ensemble QDs is modified by 2D and 3D photonic crystals structures. The aims of this research are to gain deep understanding of so-called dark exciton dynamics, which is responsible for photoblinking, and to elaborate the usage of photonic crystal structure to modify and reflect emis...