Correlation of Lattice Disorder with Crystallite Size and the Growth Kinetics of Mn²⁺ Doped ZnO Nanocrystals Probed by Electron Paramagnetic Resonance

Abstract

The correlation of the lattice disorder with the nanocrystal average size, in ZnO nanocrystals synthesized by several different methods, has been quantitatively monitored by line shape analysis of the multifrequency electron paramagnetic resonance (EPR) spectra of low concentrations of substitutional Mn2+ probing ions. The observed correlation between the line broadening parameter of the spectrum and the average ZnO nanocrystals size, independent of the synthesis procedure of the ZnO nanocrystals, demonstrates the dominance of the size related strain/disorder. On the basis of this result, a new method for determining the average ZnO nanocrystal size from the quantitative analysis of the EPR spectra of the Mn2+ probes was derived. The nanocrystallization of the disordered ZnO formed by the thermal decomposition of hydrozincite was monitored using this procedure. The observed ZnO nanocrystallite growth kinetics at lower temperatures was described by a structural relaxation mechanism consisting of the local ordering by rearrangements of the atoms in the interfaces/grain boundaries, with a growth activation energy of ∼23 kJ/mol. When the nanostructured ZnO was more than 75% crystallized, another growth mechanism of the nanocrystals was found to occur, driven by the reduction of the total grain boundary energy.

Correlation between structural and electronic order–disorder effects and optical properties in ZnO nanocrystals

“…Although dened ZnO nanostructures with different morphologies have been reported using a variety of procedures, [7][8][9][10][11][12]29 existing methods require either harsh conditions, complex procedures or long reaction times. In addition, although it is well-known that the presence of lattice defects plays a key role in the physical and chemical properties of ZnO nanostructures, 10,11 many questions still remain due to the lack of conclusive evidence for defects responsible for luminescence properties.…”

“…In addition, although it is well-known that the presence of lattice defects plays a key role in the physical and chemical properties of ZnO nanostructures, 10,11 many questions still remain due to the lack of conclusive evidence for defects responsible for luminescence properties.…”

“…11,[24][25][26] However, the origin and the inuence of disorder in nanoparticles are still under debate. The term "disorder" can be misleading because it is used to encompass a very large number of different phenomena.…”

EPR detection of sphalerite ZnO in mechanically treated ZnO+0.1C nanosystem

“…The sextet lines can be seen in EPR spectra of colloidal Mn 2 þ :ZnO Wt quantum dots after a thermal treatment at 100°C [29]; in annealed Mn-doped ZnO Wt nanoparticles [30]; or in the Zn 1 À x Mn x O nanostructures synthesized via the microwave-assisted hydrothermal method [31]. In previous studies [34][35][36], Mn 2 þ EPR sextets (like S(II)) were attributed to highly disordered nanocrystalline ZnO Wt (Table 1).…”

“…In polycrystalline samples with a wide spread of the axial distortion parameter D, (ΔD or s(D) in [34][35][36]), a singularity of finestructure transitions75/2, m2 7 3/2, m and 73/2, m2 7 1/2, m (m is components of nuclear spin I) is broaden and has recorded only the central singularity transitions À 1/2,m2 þ 1/2,m. These singularities in the polycrystalline EPR spectrum of Mn 2 þ ions in ZnO Wt occur at θ 1 ¼90°and θ 2 ¼57°(in the general case, the θ 2 value can be determined using the expressions (2)).…”