Synthesis of Colloidal Quantum Dots with an Ultranarrow Photoluminescence Peak

Localization of exciton wavefunctions away from the inorganic–organic interface is proposed for synthesizing colloidal spheroidal quantum dots (QDs) with an ultranarrow photoluminescence (PL) peak width. This strategy is demonstrated by synthesizing uniform-alloy Cd_xZn_1–xSe and Cd_xZn_1–xSe/ZnSe/ZnS core/shell QDs. For blue-emitting QDs, the ensemble PL full width at half-maximum (fwhm) reaches 10.2 nm and the corresponding single-dot PL fwhm is 5.2 nm. The ensemble and single-dot PL fwhm values for green-emitting QDs are 16.3 and 9.7 nm, respectively. These record-low PL fwhm values for spheroidal QDs are close to the requirements for ideal displays. To control the composition homogeneity, the synthetic scheme is separated into four consecutive steps, namely, nucleation of monodisperse CdSe core QDs, epitaxial growth of thickness-controlled CdSe/ZnSe core/shell QDs with a low degree of spontaneous alloying, Cu-catalyzed alloying for uniform-alloy QDs, and additional epitaxy of outer ZnSe and ZnS shells onto uniform-alloy Cd_xZn_1–xSe QDs. Among all metal ions tested, copper ions are identified to be the best catalysts for forming uniform-alloy Cd_xZn_1–xSe QDs, which can enter a QD rapidly to initiate alloying and effectively exit a QD after the alloying process under the experimentally feasible conditions.