Controllable Synthesis and Optical Properties of ZnS:Mn 2+ /ZnS/ZnS:Cu 2+ /ZnS Core/Multishell Quantum Dots toward Efficient White Light Emission

The ability to control dopants and defects, as well as the core/shell structures, of quantum dots (QDs) is an essential nanotechnology to modify and optimize their photoluminescence properties. Herein, the optimized ZnS:Mn²⁺/ZnS/ZnS:Cu²⁺/ZnS core/multishell QDs have been prepared, and their luminescence properties depending on the ratios of the starting materials and the injection temperature of an extra sulfur source were discussed; finally the white light can be possibly obtained by mixing the blue light (emission peak at 450 nm originating from Cu²⁺ dopants or emission peaks at 405 and 430 nm corresponding to a defect emission center) and orange light (emission peak at 585 nm from Mn²⁺ dopants). As a controlled synthesis comparison, the optimum core/shell structures and key synthesis parameters have been determined, and the quantum yield (QY) of the as-obtained ZnS:Mn²⁺/ZnS/ZnS:Cu²⁺/ZnS core/multishell white light emitting QDs without defect emission was determined to be 38%. The practical white light device prototype has been also fabricated and the CIE color coordinate of (0.32, 0.34) with a warm white light has been realized upon the excitation of the commercial 370 nm UV LED chip, which demonstrated potential application for micro/nano optical functional devices.