Methods for synthesizing quantum dots generally rely on very high temperatures to both nucleateand grow core and core–shell semiconductor nanocrystals. In this work, we generate highlymonodisperse ZnS and CdZnS shells on CdSe semiconductor nanocrystals at temperatures as low as65 °C by enhancing the precursor solubility. Relatively small amounts of trioctylphosphine andtrioctylphosphine oxide have marked effects on the solubility of the metal salts used to formshells; their inclusion in the precursor solutions, which use thiourea as a sulfur source, can leadto homogeneous and fully dissolved solutions. Upon addition to suspensions of quantum dotcores, these precursors deposit as uniform shells; the lowest temperature for shell growth (65 °C) yields thethinnest shells (d < 1 nm) while the same process at higher temperatures (180 °C) forms thickershells (d ∼ 1–2 nm). The growth of the shell structures, average particle size, size distribution, and shapewere examined using optical spectroscopy, transmission electron microscopy, x-raydiffraction, and transmittance small angle x-ray scattering. The photoluminescencequantum yield (QY) of the as-prepared CdSe/ZnS quantum dots ranged from26% to 46% as compared to 10% for the CdSe cores. This method was furthergeneralized to CdZnS shells by mixing cadmium and zinc acetate precursors.The CdSe/CdZnS nanocrystals have a thicker shell and higher QY (40% versus36%) as compared to the CdSe/ZnS prepared under similar conditions. These lowtemperature methods for shell growth are readily amenable to scale-up and can providea route for economical and less energy intensive production of quantum dots.