Many are the researchers trying to come up with the perfect red-emitting phosphor to add to the conventional blue-emitter/yellow-phosphor white LED to create a more balanced and pleasing white color, or as an essential element in another up-and-coming LED configuration: a UV emitter combined with blue, red, and green phosphors. Approaches to red phosphors include praseodymium-doped and other substances, as well as various sorts of quantum dots (QDs); in addition, some researchers go to great pains to try to make the red-phosphor and yellow-phosphor spectra mutually exclusive, while others are not concerned with that.
Researchers at LumiSands and the University of Washington (both of Seattle, WA) have developed a QD-based red phosphor that combines the qualities of good color rendering, low cost, and low toxicity. Unlike conventional QDs made of cadmium selenide or cadmium sulfide, the Washington researchers’ QDs in their phosphor are silicon (Si)-based. To create the QDs, a silicon wafer was etched to make it porous and the resulting material scraped off, etched, passivated, and mixed with diphenylsilanediol in ethanol. The result is 1- to 5-μm-diameter particles with 5-nm-diameter QDs on their surfaces. The phosphor has a photoluminescence quantum yield (PLQY) of 51% and 41% using 365 nm and 405 nm excitation, respectively. Used in warm-white LEDs, the phosphor enables a color-rendering index of around 95, showing very high-quality white light. Contact Chang-Ching Tu at [email protected].