CDS NANOCLUSTERS - SYNTHESIS, CHARACTERIZATION, SIZE-DEPENDENT OSCILLATOR STRENGTH, TEMPERATURE SHIFT OF THE EXCITONIC-TRANSITION ENERGY, AND REVERSIBLE ABSORBENCY SHIFT

Improved synthetic routes and size-selective precipitation have enable d the preparation of almost monodisperse CdS clusters. Six samples of 1-thioglycerol stabilized clusters with diameters of approximately 13, 14, 16, 19, 23, and 39 Angstrom A have been prepared as fully redispe rsible powders and were characterized by elemental analysis, powder X- ray diffraction, electron microscopy, thermogravimetric analysis, and UV-vis spectroscopy. Small-angle X-ray scattering was used to determin e the mean cluster size. The well-structured UV-vis spectra reveal tha t the size-dependent shift of the 1s-1s excitonic transition is in agr eement with the tight-binding theory and the pseudopotential theory. M oreover, as expected by quantum mechanical calculations the oscillator strength of the transition increases proportional to 1/r(3). UV-vis s pectra taken at various temperatures between 4 and 295 K have shown th at the temperature shift of the excitonic transition energy becomes st ronger with decreasing particle size. Strong, reversible absorbance sh ifts were observed, upon transferring the clusters from their solution s onto quartz plates and vice versa.