Electronic states of semiconductor clusters: Homogeneous and inhomogeneous broadening of the optical spectrum

Abstract

The ho~ogeneous. (single-cluster) and in~omogeneous contributions to the low temperature electronic absorptIon spectrum of 35-50 A diameter edSe clusters are separated using transient photophysical hole burning. The clusters have the cubic bulk crystal structure but their electr.onic states are strongly quantum confined. The inhomogeneous broadening ~f these featu~es ~n~es because t~e spectrum depends upon cluster size and shape, and the samples contam SImIlar, but not Identical, clusters. The homogeneous spectrum, which consists of a peak 14? cm -I (17 meV) .wide, with a phonon sideband and continuum absorption to higher energy, IS compared to a simple molecular orbital model. Electron-vibration coupling, which is enhanced in small clusters, contributes to the substantial broadening of the homogeneous spectrum. The inhomogeneous width of the lowest allowed optical transition was found to be 940 cm -I, or seven times the homogeneous width, in the most monodisperse sample.

Spectroscopic characterization of streptavidin functionalized quantum dots

“…The lowest energy band in the absorption spectra of the quantum dots is labeled 1S 3/2 <-1S e , where 1S 3/2 and 1S e are conventional descriptors for the HOMO and LUMO of a CdSe dot and the arrow points in the direction of the electronic transition (33). Higher energy transitions (e.g., 1P 3/2 ← 1S e ) appear as shoulders on a continuum of increasing extinction coefficient with decreasing wavelengths (10). Spectral hole burning experiments have shown the fine structure of the electronic transitions buried under the broad bands which correspond to atomic transitions of single dots (10).…”

“…Here, E 1S 3/2 <−1S e is the energy of the first electronic transition, as calculated from the absorption spectrum (2.4 eV for QD525; 2.16 eV for QD585), E g is the band-gap energy for bulk material (1.84 eV for CdSe), a b is the exciton Bohr radius (5.6 nm for CdSe), a dot = radius of the Qdot, and R y * is the Rydberg constant (0.016 eV for CdSe) (8,10,11). We can thus estimate the respective core sizes of QD525 (b in Figure 1A) and QD585 (c in Figure 1A) to be 2.8 nm and 3.6 nm.…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…Since the pioneering work of Brus, Ekimov, and many others in the early 1980-1990s [1][2][3][4][5][6][7][8][9][10][11][12][13], the study of semiconductor nanocrystals (NCs) has developed into a mature, dynamic and multidisciplinary research field, which attracts increasing attention worldwide, both for its fundamental challenges and its potential for a number of technologies (light emitting devices, solar cells, luminescent solar concentrators, optoelectronics, sensing, thermoelectrics, biomedical applications, catalysis) [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. Colloidal semiconductor NCs are particularly attractive, since they consist of an inorganic core that is coated with a stabilizing layer of (usually) organic ligand molecules.…”

Fabrication and Optical Characteristics of CdS/Ag Metal-Semiconductor Composite Quantum Dots

“…[4][5][6] In particular, a radiolysis method utilizing a gamma ray source at room temperature has been actively and successfully conducted, which allows us to monitor the size of the sample during each fabrication process.…”

“…2,3 However, recently, many research groups have established chemical fabrication methods of colloidal QDs dispersed in solution, which are comparatively more stable than those in glasses. [4][5][6] In particular, a radiolysis method utilizing a gamma ray source at room temperature has been actively and successfully conducted, which allows us to monitor the size of the sample during each fabrication process. [7][8][9] These colloidal QDs are produced by chemical reactions in equilibrium states, where the solution matrices act as a stabilizer, offering fast reaction time between the atoms as well as a slow growth rate during the fabrication procedure, helping to improve stability.…”