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This project funded by ACS aims to better understand the underlying difficulties of doping of semiconductor quantum dots. We address questions how the dopant impacts the nanoparticles during growth in colloidal solutions. As a model system, we have been investigating CdSe nanoparticles grown from single precursors in the heterogeneous growth regime when multiple distinct sized nanoparticles are present. In the past we have explored the effect of indium dopant on the growth kinetics and we started expanding our studies to gallium and tin doped CdSe nanoparticles. Chemical analyses of the particles have shown that all of these dopants are found within the CdSe particles. The indium dopant accelerated the growth of CdSe units, but the gallium dopant exhibit a saturation effect in the acceleration of particle growth. In contrast to the indium and undoped CdSe nanoparticles, we have found that the tined doped samples produces twinning planes in the CdSe nanoparticles. Terahertz spectroscopy shows that the tin doped CdSe nanoparticles exhibit an upward shift in their Froehlich band at 208 cm^-1. Dopant not only can accelerate the growth of the nanoparticles , but we found an increased oxidative etching rates of the tin doped particles in amines compared to the undoped CdSe nanoparticles. We are carrying out experiments to assess if the dopants are directly or indirectly involved in the increased etching rates. The results will be communicated soon.

We have also found that the addition of ZnS shell greatly impacts the temperature dependant photoluminescence of the particles. The strong temperature dependant component of the doped nanoparticles disappears when the ZnS shell thickness is increased. At this point, we speculate that the dopant could migrate into the shell as a result of the better size match of with the ZnS crystal lattice.

In addition to the above studies, we realized that CdSe material will not be sufficient to address solar energy needs on the global scale. We started exploring the synthesis of sustainable nanoparticles that could be used as a platform for our doping studies. We are the first to develop the colloidal synthesis of crystalline b-FeSi₂ nanoparticles. These particles will be used in our future doping studies. In addition, based on our previous observation of heterogeneous growth of the CdSe nanoparticles, we have developed an approach called the quantized Ostwald Ripening that could be a potential method to produce size focusing of nanoparticles in a colloidal solution.