Influence of SPP co-stabilizer on the optical properties of CdS quantum dots grown in PVA

Quantum dots of cadmium sulfide have been synthesized in a series of aqueous solutions of two stabilizers: a fixed concentration of polyvinyl alcohol polymer with a variable amount of sodium polyphosphate. Optical absorption and photoluminescence measurements have been performed in order to assess the optical properties of the colloidal solutions. Transmission electron microscopy images have been recorded to obtain structural information of the nanocrystals. The results obtained from the spectroscopic techniques reveal two different behaviors as the amount of sodium polyphosphate is increased in the samples. The photoluminescence of quantum dots in a polyvinyl alcohol solution without sodium polyphosphate is quenched. The addition of this co-stabilizer activates the luminescence, being more intense and blue-shifted as the amount of sodium polyphosphate is increased. However, further addition of this product beyond a organic polymer-co-stabilizer weight ratio of 1:6.25⋅10−3 leads to the inverse behavior: a decreasing luminescence intensity and a red shift of the emission peaks are found. Transmission electron microscopy measurements indicate that a deagglomeration of the particles is produced as the amount of co-stabilizer is increased.