Rare-earth-doped GaN switchable color electroluminescent devices

Switchable color (SC) light emission has been obtained from thin-film electroluminescent devices (ELDs) which use green Er- and red Eu-doped GaN phosphors. These two-electrode SCELDs can switch color through variation of applied bias. Different SCELD structures, which share in common a stacked GaN: Er/GaN: Eu phosphor layer, can be implemented for use with DC or AC operation. A single SCELD can emit green (537/558 nm), red (622 nm), yellow, and orange. For the DC-SCELD, an electrically rectifying GaN/p-Si interface allows polarity-dependent current paths, which induce selective luminescence of red or green phosphor layers. For the AC-SCELD, as the bias frequency is increased, bright red emission from GaN: Eu saturates while green emission from GaN: Er increases and becomes dominant. The AC-SCELD exhibits brightness levels >10 cd/m/sup 2/ and can change chromaticity coordinates by as much as /spl Delta/x>0.32 and /spl Delta/y>0.33. Application of these devices to switching between other visible and/or infrared wavelengths is envisioned based on appropriate choice of luminescent dopants in the GaN layers.