The fabrication of the metal/semiconductor quantum dot composites for enhanced nonlinear optical devices

Composite materials of structured nanoparticles that consist of a metallic core and nonlinear shell or a nonlinear core and metallic shell has been shown to provide substantial further enhancement in the speed/power performance of nonlinear optical device. The main emphasis of this work is placed on the examination and development of the chemical routes of preparation that would produce such composites. Nonlinear optical studies on CdSe{dollar}rmsb xTesb{lcub}1-x{rcub}{dollar} nanocrystallite doped glasses are also included.; Coated nanocrystallites embedded in liquid solutions or in silicate glasses, involving Ag/AgBr, Ag/CdS, Ag/CuCl, and Ag/Zn{dollar}rmsb xCdsb{lcub}1-x{rcub}{dollar}S(CdS{dollar}rmsb xSesb{lcub}1-x{rcub}{dollar}) composite systems, have been synthesized by photo-chemical reduction/deposition, conventional melt/quench, and ion diffusion methods. The resulting coated nanocrystallites exhibit absorption spectra which are red-shifted and broadened, as compared to the surface plasmon absorption of homogeneous silver nanoparticles. The theoretical model based on an effective medium theory for both metal coated semiconductor and semiconductor coated metal nanoparticles is presented. The calculated absorption spectra of coated nanoparticles reproduce the significant features of the experimental absorption spectra. These composite nanoparticles are also characterized by photoluminescence, x-ray diffraction, transmission electron microscopy, and electron diffraction. The results provide further evidence that the particles are coated. A brief discussion of the relative thermodynamic stability between CdS and Ag{dollar}sb2{dollar}S and of the reduction mechanism for Ag{dollar}sp+{dollar} ions diffused in CdS{dollar}rmsb xSesb{lcub}1-x{rcub}{dollar} or Zn{dollar}rmsb xCdsb{lcub}1-x{rcub}{dollar}S doped glasses is presented.; The nonlinear optical absorption saturation of CdSe{dollar}rmsb xTesb{lcub}1-x{rcub}{dollar} doped glasses has been studied using a femtosecond time domain Z-scan experiment with an open aperture. We have measured the effects of saturation versus wavelength and incident power, and observed a large absorption saturation in these glasses although we have not reached the saturation limit at 780 nm and 790 nm. A comparison has been made to nanoparticle composites of different stoichiometries. The CdSe{dollar}rmsb xTesb{lcub}1-x{rcub}{dollar} microcrystallite doped glasses have a lower-intensity threshold and a larger absorption change in respect to the CdS{dollar}rmsb xSesb{lcub}1-x{rcub}{dollar} nanocrystallite doped glasses.