An Optical Spectroscopy Study of Ionic Defects: Ni²⁺Ions in Tetrahedral Coordination

Exploring LiZnNbO4 as a Host for New Colored Compounds: Synthesis, Structure, and Material Properties of NbZn1‐x Mx LiO4 (M=Mn, Co, Ni, Fe) and Nb1‐ySby Zn1‐x Mx LiO4 (M=Co, Ni)

“…The binding energy separation between the 2p 1/2 and 2p 3/2 states is observed to be ~15.8 eV. It has been shown that the binding energy separation between 2p 1/2 and 2p 3/2 is ~15.7 for Co 2+ ions occupying a tetrahedral coordination [37,48] . The XPS investigations not only confirm the oxidation state of Co 2+ ions, but also gives an idea about the possible coordination as well.…”

“…Of these, 3 T 1 (F)→ 3 T 1 (P), is observed in the visible region [26,47] . The broad transition centered around 1.8 eV may correspond to this transition [48] . The other transition centered at 2.9 eV has two shoulder peaks: at ~2.8 eV and the other at ~3.1 eV.…”

Lignin Depolymerization by Catalytic Hydrodeoxygenation Performed with Smectitic Clay‐Based Materials

“…[ 36 ] Furthermore, there was no recording of the characteristic doublet at about 600–640 nm for nickel species in tetrahedral symmetry (Ni(O d )), which could have confirmed the presence of NiAl 2 O 4 . [ 37 ] This doublet could have been masked by the large Ni(O h ) band, though, as per the following Raman analysis. In the spectrum of the calcined material, the weakenings of the main bands typically of Ni(O h ), together with the relative increase in intensity of the charge transfer band at 279 nm, are all indicating changes in the coordination sphere of Ni, in part due to pillar dehydration.…”

Synthesis and characterization of nonstoichiometric NiGa2O4 transparent thin films

“…However, asymmetric shapes of the O-II band at room temperature and elevated temperatures indicate an overlap with transitions of Ni 2+ located on tetrahedral sites. Indeed, in the isostructural NiAl 2 O 4 spinel, two sharp absorption bands from Ni 2+ in tetrahedral sites have been observed in this region [10]. From the temperature dependence of optical spectra, it can be concluded qualitatively that most of the Ni 2+ ions occupy the octahedral sites at low temperatures and that the increasingly asymmetric shape of the band O-I and O-II provides evidence for an increasing concentration of Ni 2+ ions in tetrahedral sites with rising temperatures.…”

“…In most of the spinels, x is between 0 and 2/3 (largely normal) or between 2/3 and 1 (largely inverse). With the input of energy to a spinel system, e.g., by increasing the temperature or by mechanochemical milling, x approaches the random distribution [9,10].…”