Suppression of Red Luminescence in Wire Explosion Derived Eu:ZnO

Abstract

Europium oxide (Eu₂O₃) is coated on zinc (Zn) wire using the electrophoretic deposition process. The coated Zn wire is subjected to the wire explosion process (WEP) which is rapid (< 15 min), and chimie douce (soft chemical, low temperature), in nature; this results in the formation of Eu doped ZnO. The explosion chamber contains oxygen (99.9%) at atmospheric pressure. Electron micrographs indicate that the particle sizes are ∼ 80 nm. Diffractogram-based analysis suggests that the crystallite size is ~ 18–20 nm in the as-prepared doped ZnO nanoparticles. Electron paramagnetic resonance shows the presence of Zn vacancies and the cryo-photoluminescence spectrum indicates that Eu exists in the + 3 state. A combined Williamson–Hall plot and Kisielowski’s model based analysis indicates that Eu is a substitutional dopant in WEP derived Eu:ZnO particles. It is estimated that this material has ∼ 0.24 at.% doping. This analysis also shows that, unlike another popular material GaN, in the case of ZnO, Eu³⁺ strictly substitutes for Zn²⁺ (i.e., dopant replacing a cation–anion pair does not seem possible). It may be noted that Eu³⁺ in a suitable host is oftentimes reported to be an efficient luminophore. The IR spectra show a band shift from 486 cm⁻¹ to 493 cm⁻¹; with peak shifts from 436 cm⁻¹ to 430 cm⁻¹ in Raman spectra. These too indicate the presence of Eu in the samples. However, at room temperature, only green luminescence (centered at 534 nm) is observed from the sample indicating (1) high concentrations of O_Zn anti-site defects and Zn vacancies, and (2) concomitant quenching of the luminescence at room temperature. Our results suggest that WEP is viable for synthesizing rare earth doped ceramic materials. However, obtaining efficient phosphors using this approach will likely require, (1) reduction of defect densities, and (2) appropriate passivation using post-processing.