Optical properties of CdS nanocrystallites embedded in (Si0.2Ti0.8)O2 sol-gel waveguide

We report on the implementation of a two-grating coupler technique for measurement of repopulation of deep traps in CdS nanocrystallites embedded in a (Si0.2Ti0.8)O-2 waveguiding glass layer of high refractive index. A sol-gel process is used to produce this waveguide. The low attenuation (similar to 1 dB/cm) of the waveguide allows to in-and out-couple light by surface relief gratings embossed on the top layer of the waveguide. The spectral region of waveguiding (approximate to 700 nm) that was studied corresponds to the deep trap spectral position in CdS. The waveguiding beam is used as a probe beam and we used the third harmonics of a YLF:Nd laser (347 nm) as a pump. The influence of bimolecular recombination on repopulation of deep traps is demonstrated, The linear recombination time as well as bimolecular and Auger coefficients are determined. (C) 1998 Elsevier Science B.V.