Size quantization in small semiconductor particles

Abstract

Optical effects due to size quantization in three dimensions have been observed for CdS and PbS colloids with particle diameters less than 50 8, and 20 to 200 A, respectively. The optical absorption edge is blue shifted -0.9 eV for the CdS colloid; for PbS colloids the shift is -2 eV for particle diameters 20-30 A, and -1 eV for particle diameters 50-200 A. The results are consistent with perturbation of the semiconductor band structure due to carrier confinement resulting in an increase in the effective band gap, pictures of the colloids, Ken Marsh and John Connolly for obtaining emission spectra, and Brad Thacker for technical assistance in several experiments. A.J.It is shown that the SI state of 1H-indazole in acetic acid undergoes double proton transfer along the hydrogen bonds in the indazole-acetic acid complex. The proton transfer converts 1H-indazole into 2H-indazole. The rate of proton transfer is estimated to be 2.7 X lo9 s-I from transient fluorescence measurements.

A facile single injection Hydrothermal method for the synthesis of thiol capped CdTe Quantum dots as light harvesters

“…The absorbance spectra show a well resolved absorption peak indicating first electronic transition (1s-1s) of CdTe QDs which, red shift from 425 nm to 660 nm with increase in time, revealing the QDs growth. This profound CdTe QDs absorption peaks shift to higher energy compared to bulk CdTe material absorption peak due to Quantum confinement effect [2], which further depends on size of nanocrystals. The size of nanocrystals is influenced by reaction parameters like temperature, reflux time, pH, capping agent and concentration of source.…”

“…This phenomenon leads to renowned quantum size effect or quantum confinement effect by which nanocrystals owes its name Quantum Dots (QDs) [1][2][3]. QDs whose size is less than Bohr exciton radius of the material exhibits interesting characteristic properties than its bulk counterpart, as continuous density of states in bulk collapse into discrete electronic state leading to size tunable band gap in QDs.…”

“…QDs whose size is less than Bohr exciton radius of the material exhibits interesting characteristic properties than its bulk counterpart, as continuous density of states in bulk collapse into discrete electronic state leading to size tunable band gap in QDs. This size tunable band gap and large surface to volume ratio of QDs gives rise to unique and remarkable properties which were not observed in bulk semiconductor materials [1][2][3].…”

“…In this context, the QDs are considered as future prospective material due to their distinctive properties like Multiple Exciton Generation (MEG), larger extinction coefficient and specifically tailored band gap [1][2][3]. It is predicted that these semiconductor nanocrystals based assemblies can achieve the energy conversion efficiency much beyond Shockley Queisser limit of 31% for traditional Si based solar cell [4].…”

Synthesis of cadmium selenide quantum dots for fabrication of hybrid light emitting diodes.

“…This effect is referred to as quantum confinement. [1] The size of the particle which must be met in order to start to exhibit these characteristics is the Bohr's Radius of an exciton. Bohr's Radius of an exciton is the distance between the atom's hole and electron, or its exciton pair and, varies for each semiconductor crystal.…”