Semiconductor specks called nanocrystals may be pointing the way to lasers that shine in colors beyond the basic red and blue seen in bar-code scanners and DVD players. Semiconductors create laser light by offering electrons a choice of two energy states, lower or higher. The wavelength of light emitted depends on the band gap, or difference in energy between states, which in nanocrystals decreases with size, says Victor Klimov of Los Alamos National Laboratory. Klimov and his colleagues slashed the energy needed to make nanocrystals lase by wrapping zinc selenide around cadmium sulfide cores, producing crystals four to 20 nanometers wide. Lasers made from such two-layer nanocrystals could be cheaper and more efficient than today's semiconductor versions, which consist of layered stacks at least several microns thick. See the May 24 Nature for more illumination.