Right now, there isn't one that we know of. The article states "new phosphor from semiconductor nanocrystals of cadmium sulfide mixed with manganese." which is used to make a cleaner white color. There probably is some other combination out there that nobody has found yet that will produce a purple (or yellow) color. I just hope that there is enough demand for new colors for somebody to dump some more money into research. Unfortunately, while there might be a market for a pure white LED, the market for a Purple LED just isn't nearly as big. No demand = no money in it = no research = no purple LEDs :(