Photoluminescence studies on structural defects and room temperature ferromagnetism in Ni and Ni–H doped ZnO nanoparticles

Abstract

We explore the effects of hydrogenated annealing on the crystal structure, room temperature ferromagnetism (RT-FM) and photoluminescence (PL) properties of Ni-doped ZnO (Zn1−xNixO, x=0.0 to 0.2) nanoparticles prepared by a sol-gel method. The x-ray photoelectron spectra and x-ray diffraction data provide evidence that Ni has been incorporated into the wurtzite ZnO lattice as Ni2+ ions substituting for Zn2+ ions at x≤0.05. A secondary phase of NiO type begins to form inside ZnO when x>0.05 and segregates from ZnO host lattice at x=0.2, leading to a large variation in the lattice constants of ZnO. The magnetization measurements show that the saturation magnetization (Ms) increases with increasing Ni concentration in the single-phase Zn1−xNixO (x≤0.05) nanoparticles. The secondary phase formation reduces the magnetization of Zn1−xNixO (x=0.1 and 0.15), while the segregation of NiO from the ZnO lattice at x=0.2 is accompanied by a large increase in Ms again. The PL measurements show that the UV emission intensity of single-phase Zn1−xNixO (x≤0.05) nanoparticles increases with a blueshift in the UV emission line when the Ni concentration increases, while the dominant green emission intensity decreases with increasing Ni dopant. The PL data strongly suggest that the FM in single-phase Zn1−xNixO (x≤0.05) nanoparticles is intrinsically correlated with a doping induced increase in the electron concentration in the conduction band of Ni-doped ZnO. After H2-annealing, the single-phase Zn1−xNixO:H (x≤0.05) nanoparticles show increases in both coercivity and saturation magnetization. The PL and diffuse reflectance spectra suggest that hydrogen-related shallow donors and an improved sample quality may be responsible for the H2-annealing induced enhancement of the RT-FM. The obvious correlation between FM and carrier concentration in Ni and Ni–H doped ZnO points towards a mechanism of carrier-mediated FM for Ni-doped ZnO diluted magnetic semiconductors.

Synthesis of Ni-doped ZnO nanostructures by low-temperature wet chemical method and their enhanced field emission properties

“…The similar trend of change in 2θ value after Ni doping was reported by Yu et al 34 and Tong et al 35 From the interplanar spacing obtained XRD used to estimate the lattice parameters. The (002) plane XRD peak was used for the grain size calculation and the results are shown in table I. properties of ZnO, which we already discuss in the previous report 4 .…”

Co-Precipitation Synthesis and Characterization of Nanocrystalline Zinc Oxide Particles Doped with Cu<sup>2+</sup> Ions

“…Seehra et al [38], on the other hand suggested that the CuO phase is paramagnet in the Cu x Zn 1−x O/CuO composite. Tong et al [39], and Wang et al [40] showed, that hydrogen incorporation in the sample can induced ferromagnetism. They believed, that hydrogen as shallow donor might be responsible for the enhancement of RTFM.…”

Defects induced luminescence and tuning of bandgap energy narrowing in ZnO nanoparticles doped with Li ions

“…UV and Visible bands in undoped and doped ZnO have multiple emission and frequently assigned to differentiate defects. 38 UV emission (i.e., NBE) region $350-450 nm of some selected samples, e.g., y ¼ 0, 0.06, and 0.10 samples is enlarged for convenience and can be well fitted by two Gaussian lineshape peaks shown Figs. 6(a)-6(c), respectively.…”