Preparation and characterization of cadmium sulfide quantum dot doped ORMOSILs

Organically-modified silicate (ORMOSIL) has been used as the matrix material in the preparation of CdS-doped glassy nanocomposites both in bulk and film forms. In ORMOSILs, parts of the bridging oxygen bonds in the pure silica gels were replaced by organic groups from the organically substitute alkoxysilanes which were incorporated into the tetraethylorthosilicate alcohol solutions. Polydimethylsilosane (PDMS) is mainly used as the organic component in the ORMOSILs. The dried gels were thermally treated at various temperatures to grow the CdO particles. The ORMOSIL matrix offers improved crack prevention and film forming abilities as compared to the pure silica matrix. The heat-treated gels, containing up to 20 wt% CdO, were subsequently exposed to H{dollar}sb2{dollar}S gas. CdS nanocrystallites of hexagonal wurtzite structure with average particle sizes ranging from 2 to 7 nm were then formed within a highly transparent matrix. The use of amino-propyl-triethoxysilosane as a bifunctional ligand to control the CdS particle size distribution proved to be effective. The preparation processes of the CdS doped ORMOSILs is described and some general physical properties are reported.; Linear optical properties of these CdS doped ORMOSILs were characterized by absorption, photoluminescence (PL), and photoluminescence excetation (PLE) spectroscopy. Quantum confinement effect of the CdS clusters could be found by the blue shift of the optical absorption edge and PLE peak position. PLE spectroscopy proved to be an easy and nondestructive method for determining CdS particle size and size distribution. The defect states found from the PL emission bands are closely related to the preparation process conditions.; Nonlinear optical properties of these quantum-confined nanocomposites were studied by using degenerate four-wave mixing and pump-and-probe techniques. The {dollar}chisp{lcub}(3){rcub}{dollar} values of the CdS doped ORMOSILs measured by DFWM at 532 nm by a 25 ps pulse width laser range from 10{dollar}sp{lcub}-11{rcub}{dollar} to 10{dollar}sp{lcub}-13{rcub}{dollar} esu. The imaginary part of {dollar}chisp{lcub}(3){rcub}{dollar} obtained from pump-probe experiment is on the order of 10{dollar}sp{lcub}-8{rcub}{dollar} esu. The CdS doped ORMOSILs were found to be much more immune to photodarkening compared to CdS doped glasses prepared by glass fusion method. The nonlinear optical properties of the CdS doped nanocomposites are closely related to the nature of the quantum dots such as size, surface, and defects.