Structural and Optical Properties of Mg and Cd Doped ZnO Nanoclusters

Abstract

Global optimization and data-mining techniques have been used to generate the structures of Mg and Cd doped ZnO nanoclusters. The energy has been evaluated at three levels: interatomic potentials during the filtering stage, generalized gradient based (PBE) density functional theory during the refinement of structures, and hybrid (PBE0) density functional theory for the final electronic solutions used for the prediction of the cluster optical absorption spectra. The excitonic energies have been obtained using time-dependent density functional theory including asymptotic corrections. We considered three characteristic sizes of the host (ZnO) n cluster (n = 4, 6, 8) including all chemically sensible structural types as determined from their relative energy rankings and all possible dopant permutations. Thus, an exhaustive set of the solution structures could be assessed using configurational entropic contributions to the cluster free energy, which allowed us to draw a conclusion as to the oxide miscibility at this end of the size scale. With the exception of low temperature magnesium doped n = 4 and 6 nanoclusters, we find a continuous series of stable clusters. The former are predicted to disproportionate to the pure binary structures, which could be attributed to the competition between different structural types adopted by end members. The optical behavior of most stable clusters considered is contrary to the quantum confinement model.

Structure prediction of nanoclusters; a direct or a pre-screened search on the DFT energy landscape?

“…larger sized clusters), it is not surprising the n = 1-3 GM found agree with that already reported. 20,21,[59][60][61][62][63] For our predicted atomic structures for (CdSe) n , there is a reasonable agreement with structures suggested by Sanville et al 63 Their CdSe configurations were data-mined from ZnS GM 50,68 that correspond to our 1a, 2a, 3a, 4a, 5b, 6a, 7a, 8a, 9a, 11a and 12a for CdSe. Our 5a, which is also the GM for (ZnO) 5 , (MgO) 5 and (KF) 5 , is only 0.024 eV lower in energy than our 5b for (CdSe) 5 .…”

Band Gap Engineering of Mg Doped ZnO Nanorods Prepared by a Hydrothermal Method

“…The zinc oxide (ZnO) nanostructure comes forward from among the II‐VI semiconductors with very attractive properties such as the exciting binding energy of 60 meV at room temperature and a direct wide band gap of 3.37 eV. These properties have been used for the development of optoelectronic materials and applications …”

“…Moreover, gallium‐doped ZnO is also an important material due to its high carrier concentration and electrical conductivity, especially higher gallium doping produces a decrease of the band gap values of ZnO. Among these various doping elements, cadmium decreases to approximately 3 eV and magnesium increases the band gap to 4 eV and higher . In addition, magnesium doping might be suitable for enhancement of structural, electrical, and optical properties of ZnO.…”

Optical excitation of MgO nanoparticles; a computational perspective

“…The lowest excitations of Zn doped small MgO clusters -(Zn 1Àx Mg x O) 4 , (Zn 1Àx Mg x O) 8 -were also recently predicted by Woodley and co-workers. 17 In this paper we focus on the evolution of the absorption spectrum of MgO nanoparticles with particle size. In contrast to the embedded cluster calculations discussed above, we treat the whole nanoparticle quantum mechanically.…”