Structural Evolution in an Annealed (Eu, Tb)-Doped ZnO/Si Nanoscale Junction: Implication for Red LED Development

Abstract

Codoped (Tb,Eu) ZnO films grown by magnetron sputtering on a silicon substrate and annealed up to 1200 °C showed intense photoluminescence (PL) emission from Eu3+ ions. The high-temperature annealing led to diffusion and segregation of rare earth (RE) elements toward the bottom of the film, which induced the formation of nanometric Zn-free inclusions responsible for remarkable PL emission intensity. Combined electron diffraction, chemical contrast imaging, and optical studies of these nanometric phases have been carried out. Large inclusions of zinc silicates and RE silicates a few hundreds of nanometers in size were observed, embedded in a silica phase. The structural determination of these RE-rich inclusions was carried out by combining atomic Z contrast imaging (high-angle annular dark-field imaging) and precession electron diffraction data. Upon annealing at 1200 °C, it appeared that the structure was related to an F-type disilicate structure. Energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy experiments were carried out to determine the ratios between elements and the oxidation states of the RE elements in the abovementioned inclusions. A (Tb,Eu)2Si2O7 formulation is proposed from dynamical precession electron diffraction tomography refinements, leading to a +III valence state for the RE species in agreement with spectroscopic results. PL modeling is also in good agreement with the experimental data. These results complete those obtained at 1100 °C for which the inclusions were identified as some RE10–x (SiO4)6O2–x oxyapatite structures and pointed out a combined structural and PL properties’ evolution between 1100 and 1200 °C annealing temperatures.

Mn-Modified ZnO Nanoflakes for Optimal Photoelectrochemical Performance Under Visible Light: Experimental Design and Theoretical Rationalization

“…At the same time, suitable nanostructured morphologies provide large surface area for light harvesting and photocatalytic activity, while also maintaining efficient pathways for charge and molecule transport and photocurrent generation. − ZnO doping is promising for utilizing the visible-light spectrum and electron–hole separation. − It is essential to determine appropriate dopants and their optimal presence in the ZnO lattice in order to optimize the optical and electronic properties of ZnO. In this context, rare-earth elements are excellent choices as dopants, due to their special electronic shell structure and optical features at different energy levels. − It is expected that Mn with a comparable ionic radius to that of Zn can be doped inside ZnO nanostructures to enhance the optical properties under visible illumination. , Gao et al demonstrated how Mn ions could easily replace Zn ions due to the comparable ionic radii . Studies on Mn-doped ZnO substantiate the fact that the interaction between Mn and ZnO can influence the electronic properties and bandgap of the material.…”

“…In this context, rare-earth elements are excellent choices as dopants, due to their special electronic shell structure and optical features at different energy levels. 21 − 25 It is expected that Mn with a comparable ionic radius to that of Zn can be doped inside ZnO nanostructures to enhance the optical properties under visible illumination. 26 , 27 Gao et al demonstrated how Mn ions could easily replace Zn ions due to the comparable ionic radii.…”