Light-emitting diode phosphors provide more diffuse light, which is desirable for many applications. Remote phosphor designs are also more tolerant of variations in the LED emissions spectrum. A common yellow phosphor material is cerium-doped yttrium aluminium garnet (Ce:YAG). White LEDs can also be made by coating near-ultraviolet (NUV) LEDs with a mixture of high-efficiency europium-based phosphors that emit red and blue, plus copper and aluminium-doped zinc sulfide (ZnS:Cu, Al) that emits green. This is a method analogous to the way fluorescent lamps work. This method is less efficient than blue LEDs with YAG:Ce phosphor, as the Stokes shift is larger, so more
Laser diode frequency doubling of near-IR VECSEL emitters to produce blue and green light. External-cavity diode lasers are tunable lasers which use mainly double heterostructures diodes of the AlGaAs type. The first external-cavity diode lasers used intracavity etalons and simple tuning Littrow gratings. Other designs include gratings in grazing-incidence configuration and multiple-prism grating configurations. Laser diodes have the same reliability and failure issues as light emitting diodes. In addition they are subject to "catastrophic optical damage" (COD) when operated at higher power. Many of the advances in reliability of diode lasers in the last 20 years remain proprietary to their developers. The