This thesis defense will cover a project in which cadmium acetate and kinetically controlled thiourea and selone precursors were used to synthesize 3 monolayer-sized cadmium sulfide and cadmium selenide nanoplatelets. The homogeneous nucleation and growth through controlled precursor conversion demonstrated here by scanning transmission electron microscopy (STEM) and optical spectroscopy make the nanoplatelet system ideal for fine tuning and studying compositional growth. Nanoplatelet heterostructures including different types of graded core/crown nanoplatelets were synthesized through the injection of mixed sulfur and selenium precursors with carefully selected conversion rates. The UV-vis absorption and photoluminescence emission spectral evolutions confirm the elemental distribution within the nanoplatelets and the relative precursor conversion rates over time. Nanoplatelet structures analyzed by STEM electron energy loss spectroscopy (EELS) correlate well both predictions made with precursor conversion rates, optical data, and theoretical calculations.