Controlled Mixed Violet-Blue-Red Electroluminescence from Eu:Nano-Phosphors/ZnO-Nanowires/p-GaN Light-Emitting Diodes

Europium (Eu):Y2O3-nanoparticles/Mg:ZnO-nanowires/p-GaN and (Eu):chelate-based light-emitting diode (LED) structures have been fabricated, showing controlled mixed near-UV, violet, and red electroluminescence from trivalent europium. The magnesium (Mg)-doped ZnO (Mg:ZnO)-nanowires/p-GaN heterojunction were integrated into the LED structure and were covered on the top with the nanoparticle of yttrium oxide doped with trivalent europium ions (Eu3+:Y2O3) or by Eu:chelate. Samples exhibit mixed UV/blue light at similar to 384 nm coming from the Mg:ZnO structure and a sharp red emission at similar to 611 nm related to the intra4f transition of Eu ions. It is found that with Mg doping of ZnO, the emission wavelength of LEDs in the near-ultraviolet region is shifted to a smaller wavelength, thus being better adapted to the trivalent europium excitation band. Radiative energy transfer is achieved through the strong overlap between the emission wavelength from n-(Mg:ZnO)/p-GaN heterojunction and F-7(0)-L-5(6) absorption of Eu3+ ions in the case of Eu:Y2O3 or of the (Eu):chelate intensive absorption bands. Indeed, the (Eu):chelate/(Mg:ZnO)-nanowires/p-GaN structure appears to be more adapted to UV/blue and red dual emission than Eu:Y2O3, for which low absorption prevents efficient emission. Our results demonstrate that the designs of nano-LED structures and of the chelate ligands are crucial to enhance the performance of electroluminescence devices based on ZnO nanowire arrays and rare-earth metal complexes.