BS in Materials Engineering
Materials Engineering Department
The objective of the process is to synthesize quantum dots that will fluoresce over the visible spectrum of 450 to 650nm; then to mix the quantum dots together in a polymer matrix so that when illuminated with a blue LED the mixture yields “white” light. The current quantum dot synthesis is a chemical process that involves adding a room temperature Se-TOP precursor to a 225°C Cd precursor solution to cause nucleation and growth of nanoparticles. This method, however, only yields quantum dots that fluoresce in the 520 to 600nm range. In order to create the “white” light phosphor replacement, red quantum dots need to be produced; to resolve this issue, numerous variables were isolated and adjusted. A synthesis temperature of 180°C, 200°C, and 240°C were tested and yielded a variation of growth rates and distribution of sizes, but no change in the fluorescence range. The system appeared to plateau around 600nm despite long reaction times. Cd:Se molar ratios were adjusted and showed that an increase of Se red-shifts the reaction. Various combinations of these variables were tested, but only managed to produce particles fluorescing at 617nm. A long-term test was then run on mixed quantum dot sizes to see if any Ostwald ripening effects would occur, which would be detrimental to the phosphor replacement, but after a month the fluorescence graph indicated no change in the solution. Different ratios of the quantum dot colors were mixed in a cuvette and placed in front of a blue LED, to simulate the application, with a filter and excited by a UV-LED at 90°. Multiple combinations of colors yielded “white” light according to CIE value standards.