Photoluminescence from Single Semiconductor Nanostructures

Abstract

We review some recent results in the spectroscopy of single CdSe nanocrystal quantum dots. By eliminating the effects of inhomogeneous broadening and ensemble averaging, single nanocrystal spectroscopy has revealed many new and previously unexpected physical phenomena. Among those discussed in this review are ultra-narrow emission lineshapes (~600´narrower than ensemble spectra), a highly polarizable emitting state in the presence of strong local electric fields, line broadening as a result of environmental fluctuations, and shifting of the emission spectra over a wide range of energies (from less than 300 meV to 80 meV). In addition, polarization spectroscopy of single nanocrystals has revealed the presence of a theoretically predicted two-dimensional transition dipole moment oriented in the xy plane of the nanocrystals. As a result, it is, in principle, possible to use polarization spectroscopy to determine the three-dimensional orientation of individual nanocrystals. These and other studies of single quantum dots have provided us with significant insight into the detailed physics and dynamics of this unique and fascinating physical system.

CdS Magic-Sized Nanocrystals Exhibiting Bright Band Gap Photoemission via Thermodynamically Driven Formation

“…For QDs, the homogeneous line width of one dot is related to excitonϪphonon coupling; ϳ50 meV fwhm was reported for a CdSe/ZnS QD at room temperature. 19,20 A large QD has relatively small line width. However, the line width of one nanocrystal ensemble depends on many factors such as the composition, size, size distribution, dispersion medium, and temperature; it is commonly acknowledged that narrow size distribution leads to small fwhm.…”

“…Therefore, both homogeneous and inhomogeneous broadening contribute to the bandwidth of their absorption and emission. 19,20 Single-sized nanocrystals without the inhomogeneous spectral line broadening are also called magic-sized nanocrystals (MSNs), exhibiting single-dot optical properties. With proper surface passivation and high crystallinity, such MSNs could be expected to produce band gap emission.…”

Surface-specific visible light luminescence from composite metal oxide nanocrystals

“…1 differ both in terms of the materials used and the nature of the luminescence effect. Absorption and luminescence in QDs involve transitions between electronic states which are extended throughout the particle volume [17][18][19]. The luminescence energies can be easily tuned by varying the particle size and shape, and they exhibit a very high quantum yield.…”

Quantum confinement induced shift in energy band edges and band gap of a spherical quantum dot

“…[6][7][8][9][10][11] The underlying phenomena behind the intriguing and valuable attributes of quantum dot is Quantum Confinement and hence investigation on the origin and effect of confinement in QD have become one of the most essential and exciting forefront fields in modern sciences. [5,[12][13][14][15][16] There are several theoretical as well as experimental efforts towards proper understanding of confinement mechanism in QDs. Theoretically, a wide verity of approaches have been employed to elucidate this phenomena.…”