Spectroscopic Properties of CdSe Nanocrystals

One of the most widely studied types of semiconductor NCs is CdSe. The hexagonal wurtzite structure that pertains for large CdSe crystals is shown in Fig. la, and a model of a nanocrystal is pictured in Fig. b. The size of such NCs can be controlled by reaction 

For core-shell NCs, this CdSe core is coated by a shell of one or more epitaxial layers of ZnS. 

In Exp. 34 on the absorption spectra of conjugated dyes, the model of a free electron in a one-dimensional box of length L is used to obtain the energy level expression 

For a more accnrate description of the energy levels of CdSe NCs, a very brief review of the band theory for bnlk semicondnctors is nsefnl. All semiconductors have a band gap 

Schematic parabolic band structure for CdSe, which has a band gap of 1.75 eV. The conduction band is labeled C, and several valence bands (V,) are shown. The filled and open circle symbols indicate the position of quantized k values mr/ai allowed for the / = 1 and n = 2 states of an NC with radius a. The solid arrow shows the / = 1 transition in which an electron is excited and a hole is created (open circle). The dashed arrow shows how the position of this n = i transition would change for a nanocrystal of smaller radius 32- (Adapted from Ref. 7.) This simple diagram is for the cubic zinc blend structure the hexagonal wurtzite structure has a small gap k= 0 between the and V2 bands. 

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Solid-State Lasers Radiative Properties of Ruby Crystals Spectroscopic Properties of CdSe Nanocrystals... 

Garland, C.W., Nibler, J.W. and Shoemaker, D.P. Spectroscopic Properties of CdSe Nanocrystals. In Experiments in Physical Chemistry, McGraw-Hill Boston, MA, 2009 p. 492. 

The ability to synthesize lattices of nanociystals have led to explorations of their collective physical properties. Thus, it is observed in the case, of Co nanociystals (5.8 nm) that, accompanying lattice formation, the blocking temperature increases. 421 FePt alloy nanocrystals yield ferromagnetic assemblies for which the coerrivity is tunable by controlling the parameters such as Fe Pt ratio and the particle size.1431 The evolution of collective electronic states in CdSe nanocrystals have been followed by optical spectroscopic methods. Compared with isolated nanocrystals, those in the lattice exhibited... 

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