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 ∼384 nm coming from the Mg:ZnO structure and a sharp red emission at ∼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 ⁷F ₀-⁵L₆ 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:Y ₂O₃, 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.