Influence of InP/ZnS Quantum Dots on the Optical Properties of Thin Azo Polymer Films

In this study, we determine the refractive index (n), extinction coefficient (k), absorption coefficient (α) and optical band gap (Eg) of thin films based on the commercially available azo polymer (poly [1-[4-(3-carboxy-4-hydroxyphenylazo) benzene-sulfonamido]-1,2-ethanediyl, sodium salt]), usually denoted as PAZO, doped with InP/ZnS quantum dots (QDs) at concentrations of 1 wt.%, 2 wt.%, and 10 wt.%. It was found that the absorption of the composite materials studied is driven by direct allowed electronic transitions, with the band gap energies tunable from 2.92 eV to 3.00 eV depending on the dopant concentration. Furthermore, the results suggest that resonance energy transfer (RET) between the InP/ZnS quantum dots and the azo polymer may occur, actively modulating the optical properties of the composite materials in the 385–750 nm spectral region, where the PAZO absorption spectrum and the emission spectrum of the QDs overlap. The theoretical calculation carried out demonstrate that the energy transfer is more efficient at 600 nm, than at 420 nm, where the two observed peaks in the emission spectrum of the dopant are positioned. We believe that the result obtained may be of interest to researchers working on improving the photoresponse of azo polymers through incorporation of quantum dots, particularly given that most studies in this field focus on cadmium-containing nanocrystals, whereas InP/ZnS quantum dots represent a more environmentally friendly alternative.