Light-emitting devices (LEDs) are gaining popularity as the cost and power consumption are decreasing and white-LEDs can replace the conventional ligh sources. White-light emission is usually generated either by coating a yellow phosphor on an InGaN blue-LED or by mixing the three primary colors (red, green, blue) using a multilayer structure or doping an active host material with several fluorescent dyes or composites. Recently, white-light emission from nanostructures has become a research area of general interest with the objective of replacing conventional light sources.[1–9] These systems are based on poly (vinyl alcohol)(PVA) and ZnO nanofibers composites,[1] magic-sized CdSe nanocrystals,[2] and a mixture of different size/composition nanocrystals,[3, 4] ZnS: Pb,[5] ZnS incorporated in porous silicon,[6] ZnSe,[7] Mn-doped ZnS,[8] and CdSe core particles with three shells of ZnS/CdSe/ZnS.[9] The fabrication of white-LED involves the coating of nanostructures on a UV-LED.

Most of these systems rely on the surface-state emission from the nanoparticles, namely ‘‘emission by chance’’, while the CdSe/ZnS/CdSe/ZnS structure relies on the combination of orangeand blue-light band-edge emission, namely ‘‘emission by design’’.[9] However, CdSe being a semiconductor with a bulk band gap of 1.74 eV, the band gap of CdSe nanocrystals depends significantly on the crystal size,[10, 11] as the effective masses are small (me ¼ 0.11 m0 and mh ¼ 0.44 m0, where m0 is free electron mass). The band gap of CdSe/ZnS core/shell nanocrystals increases from 2.126 to 2.683 eV when the crystal size is reduced from 5.2 to 1.9 nm.[11] This suggests that control over the size of the crystals is required to produce white-light emission.[2] On the other hand, wide-band-gap semiconductors, such as Ga2O3, ZnO, ZnS, and In2O3, depend very weakly on the size of the crystals, as the effective masses are large. The effective masses of me ¼ 0.35 m0 and mh are very large for Ga2O3.[12] Therefore, wide-band-gap materials can be more appropriate for this kind of applications.