TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The chalcogen element is selected from sulfur, tellurium, or selenium. Preferred Particles: The shape of the Pb-chalcogenide nanoparticles is selected from a sphere, a cube, an octahedral, or a cuboctahedral.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The Pb compound is a carboxylate of Pb (preferably Pb acetate trihydrate). The carboxylic acid is a monounsaturated omega-9 fatty acid (preferably oleic acid). The hydrocarbon solution is selected from trioctyl phosphine, or diphenyl ether. The nucleation and growth solution contains a surfactant in the form of a phosphonic acid (preferably hexylphosphonic acid, tetradecyl phosphonic acid, or octadecyl phosphonic acid); or an amine (preferably hexadecylamine, or dodecylamine). Preferred Method: The preparation of the Pb precursor further includes heating the Pb precursor to an elevated temperature of 100-200 degrees C. The Pb:chalcogen element ratio is 1:5-5:1. The heated Pb precursor is held at the elevated temperature for greater than 5 minutes. The nucleation temperature is between 200 degrees C and the boiling point of the nucleation and growth solution. The growth temperature is 100-200 degrees C. The predetermined time period for holding the Pb-chalcogenide nanoparticle solution at the growth temperature is 2-10 minutes. The method involves:(1) method (A): (a) preparing a Pb precursor by adding Pb-acetate trihydrate and oleic acid to diphenyl ether, where the diphenyl ether heated to an elevated of 100-200 degrees C; (b) holding the diphenyl ether at the elevated temperature for greater than 10 minutes after the Pb-acetate trihydrate and oleic acid are added, such that the Pb-acetate trihydrate and oleic acid are dissolved into the diphenyl ether; (c) cooling the Pb precursor to a temperature lower than 150 degrees C; (d) preparing a tellurium (Te) precursor containing Te dissolved in trioctyl phosphine, where the amount of Te is such that a predetermined Pb:Te ratio is present, when the Pb precursor is mixed with the Te precursor; (e) mixing the Pb precursor with the Te precursor to form a PbTe precursor, such that the Pb and the Te remain in their precursor form; (f) preparing a nucleation and growth solution by dissolving a surfactant in the form of an amine in diphenyl ether; (g) heating the nucleation and growth solution to a nucleation temperature between 200 degrees C and the boiling point of the solution; (h) injecting the PbTe precursor into the nucleation and growth solution heated to the nucleation temperature to form a PbTe nanoparticle solution, such that PbTe nanoparticles nucleate; (i) cooling the PbTe nanoparticle solution to a growth temperature of 100-200 degrees C; (j) holding the PbTe nanoparticle solution at the growth temperature for 2-10 minutes, such that a predetermined nanoparticle size is obtained; and (k) cooling the PbTe nanoparticle solution to a lower temperature, such that the continued growth of the Pb:Te nanoparticles is terminated; or(2) method (B): (a') preparing a Pb precursor by adding Pb-acetate trihydrate and oleic acid to trioctyl phosphine, where the trioctyl phosphine heated to an elevated temperature of 100-200 degrees C; (b') holding the trioctyl phosphine at the elevated temperature for greater than 10 minutes after the Pb-acetate trihydrate and oleic acid are added, such that the Pb-acetate trihydrate and oleic acid are dissolved into the trioctyl phosphine; steps (c)-(e); (f') preparing a nucleation and growth solution by dissolving a surfactant in the form of phosphonic acid in trioctyl phosphine; and steps (g)-(k). EXAMPLE - The shape of PbTe nanoparticles was controlled through the selection of a Pb:Te molar ratio. The reaction was carried out in a nucleation and growth solution containing diphenyl ether (DPE) with an hexadecylamine (HDA) as a surfactant. A Pb precursor was prepared by dissolving Pb acetate trihydrate (0.4 g) in oleic acid (1 ml) dissolved in DPE (10 ml). This precursor was heated to 150 degrees C for 30 minutes under argon, which resulted in the formation of a Pb oleate complex which was dried to remove excess water. After 30 minutes of heating at 150 degrees C, the Pb precursor was cooled to room temperature and mixed with a Te precursor, which was formed by dissolving amorphous Te powder in TOP (4 ml). The Te precursor was added slowly to the Pb precursor to prevent Pb Te nucleation. The amount of Te dissolved into TOP was varied for different trials in order to produce a Pb-Te mixture with different Pb:Te molar ratios. The Pb:Te solution was injected under vigorous string into a nucleation and growth solution containing HDA (0.3 g) dissolved in DPE (15 ml) held at 250 degrees C. After the injection of the Pb:Te solution into the nucleation and growth solution, the temperature of the solution was cooled to 170-180 degrees C and maintained for 3-4 minutes. Then, the reaction mixture was cooled to room temperature using a water bath. The cooled solution was mixed with an equal volume of toluene and methanol and the nanoparticles were separated from the solution by centrifuge at 6000 rpm for 5 minutes. The nanoparticles were redispersed in chloroform or toluene for further characterization. At Pb:Te molar ratio of 1:5, the method resulted in cube-shaped Pb Te nanoparticles with a mean linear dimension of 15 nm i.e. the longest dimension of several nanoparticles as determined from viewing the nanoparticles in a high resolution transmission electron microscope. The cube-shaped structure was due to the saturation of the particle facets with Te which minimized the effect of the HDA amine. At Pb:Te ratio of 5:1, the method resulted in PbTe nanoparticles with an octahedral shape and a mean linear dimension of 15 nm, where the facets of the nanoparticles were saturated with Pb atoms, leading to faster growth of the (100) facets compared to the (111), since the (111) facets were passivated by the HDA amine. At Pb:Te molar ratio of 1:1, cuboctahedral-shape PbTe nanoparticles were produced with a mean linear dimension of approximately 13 nm. In this intermediate range of Pb to Te molar ratio, the (100) facets and the (111) facets exhibited growth to form the cuboctahedral shape. Thus, the molar ratio of Pb to Te was used to control the shape of Pb Te nanoparticles.