Narrowing the Photoluminescence of Aqueous CdTe Quantum Dots via Ostwald Ripening Suppression Realized by Programmed Dropwise Precursor Addition

Ostwald ripening is the dominant particle growth mechanism in traditional routes to synthesize aqueous CdTe quantum dots (QDs), which results in a broadening of their size distribution and also their photoluminescence line width, in the case of prolonged reactions. We introduce a method to suppress the Ostwald ripening through the replenishment of precursors before size defocusing occurs in the aqueous synthetic system, which is realized through a programmed dropwise precursor (source) addition (denoted as PDPA) by a syringe pump arrangement that can control the precursor feed volume and rate. As a result, we have obtained a series of highly monodisperse CdTe QDs, with the emission full width at half-maximum in the red region (106 meV) being even narrower than that in the green region (160 meV). We monitored the conductivity of the reaction solution to follow the consumption of precursors, providing feedback as to whether the replenishment volume was matched. Correlations between the emission quantum yield and the fluorescence lifetime for different precursor source addition rates are provided. The influence of the respective sizes of the CdTe particles employed as precursors in PDPA on the growth rate, monodispersity, and emission characteristics of the resulting QDs is explored, and the underlying mechanisms are rationalized.