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Water-dispersible CdS quantum dots (QDs) emitting from 510 to 650 nm were synthesized in a simple one-pot noninjection hydrothermal route using cadmium chloride, thiourea, and 3-mercaptopropionic acid (MPA) as starting materials. All these chemicals were loaded at room temperature in a Teflon sealed tube and the reaction mixture heated at 100 °C. The effects of CdCl(2)/thiourea/MPA feed molar ratios, pH, and concentrations of precursors affecting the growth of the CdS QDs, was monitored via the temporal evolution of the optical properties of the CdS nanocrystals. High concentration of precursors and high MPA/Cd feed molar ratios were found to lead to an increase in the diameter of the resulting CdS nanocrystals and of the trap state emission of the dots. The combination of moderate pH value, low concentration of precursors and slow growth rate plays the crucial role in the good optical properties of the obtained CdS nanocrystals. The highest photoluminescence achieved for CdS@MPA QDs of average size 3.5 nm was 20%. As prepared colloids show rather narrow particle size distribution, although all reactants were mixed at room temperature. CdS@MPA QDs were characterized by UV-vis and photoluminescence spectroscopy, powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry and MALDI TOF mass spectrometry. This noninjection one-pot approach features easy handling and large-scale production with excellent synthetic reproducibility. Surface passivation of CdS@MPA cores by a wider bandgap material, ZnS, led to enhanced luminescence intensity. CdS@MPA and CdS/ZnS@MPA QDs exhibit high photochemical stability and hold a good potential to be applied in optoelectronic devices and biological applications.

Microcrystals of an organic fluorescent dye, 4-octylamino-7-nitrobenz-2-oxa-1,3-diazole, were generated using the reprecipitation method, which is a solvent exchange process. In the presence of polymers, namely, poly(acrylic acid), molecular weight 5100 g mol(-1) and 15 000 g mol(-1), and poly(acrylic acid-co-maleic acid), average molecular weight about 50 000 g mol(-1), used as their sodium salts, the reprecipitation process was strongly accelerated. The reprecipitation kinetics was monitored by UV/vis absorption spectroscopy and revealed a three-step mechanism, each step being influenced by the polymer. The size and shape of the microcrystals were analyzed by fluorescence microscopy. The microcrystals obtained in the presence of polymers were smaller and more regular than those prepared in water alone and were not agglomerated. When the polymer was placed in the reprecipitation medium before introducing the dye solution, the microcrystals displayed a rectangular shape. When the polymer was introduced 20 min after the beginning of the reprecipitation process, intricately structured flowerlike microcrystals were observed. Microanalysis revealed that the microcrystals contained noticeable amounts of polymer. The measurement of the surface electric zeta potential suggested that a proportion of the polymer was present at the microcrystal surface. This work gives a thorough insight into a field where trials have until now been performed in an empirical way. It opens new perspectives to produce low-cost organic microcrystals, potentially useful in optics or pharmaceutical sciences.