EXAFS determination of local atomic structure of selected transition metals in CdSe matrix

Co2+-Doping of Magic-Sized CdSe Clusters: Structural Insights via Ligand Field Transitions

“…Mn 2+ -doped CdSe clusters were characterized by EXAFS (Figure S9 and Table S2 in the Supporting Information) for the comparison. The length of the Mn−Se bond (2.57 Å) in doped clusters lies between those of Mn−Se bonds (2.54 Å) in bulk Mn 2+ -doped CdSe crystals 87 and Cd−Se bonds (2.60−2.61 Å) in the present clusters. Interestingly, although Mn−Se bonds are only shortened by ∼1.2% (0.03 Å) with respect to Cd−Se bonds, this deviation become about eight-times greater (9%, 0.25 Å) in the case of Co 2+ doping.…”

“…(d) Extrapolated bond lengths obtained from the 4 A 2 – 4 T 1 (P) transition in MCD spectra as functions of D q. The blue dot represents Co–Se bond length in Co 2+ -doped CdSe bulk crystals, and the two red dots correspond to the estimated Co–Se bond lengths of Co 2+ -doped CdSe clusters for cases of n = 5 and n = 6 in eq .…”

“…(d) Bond lengths of Co 2+ -doped CdSe clusters determined by EXAFS analysis. Cd–Se and Co–Se bond lengths (black and blue dashed lines, respectively) in bulk Co 2+ -doped CdSe crystals and the Co–Se bond length estimated by MCD spectroscopy (the range between two red dashed line) are presented for comparison.…”

“…0.05 Å for a QD diameter of ∼1.3 nm and 0.02 Å for a QD diameter of 2.5 nm88 ), which might reflect the structural flexibility of the clusters. Remarkably, EXAFS analysis estimates the Co−Se bond length as ∼2.36 Å, which is significantly shorter than both Co−Se bonds (2.44 Å)87 in bulk Co 2+ -doped CdSe crystals and Cd−Se bonds in clusters (2.60−2.61 Å). The obtained results are in good agreement with the value determined by MCD ligand field analysis (2.35−2.37 Å), validating the suitability of the magneto-optical approach for extracting structural information.…”

“…Figure 1b), and thus, the position of dominant MCD minimum is taken as the transition energies in our approach. On the basis of the Co−Se bond length in Co 2+ -doped CdSe bulk crystals (2.44 Å, 87 which is depicted as a blue dot in Figure 3d), we extrapolated the expected bond lengths assuming the cases of n = 5 and n = 6 in eq 2 (black dashed lines in Figure 3d). Consequently, the region enclosed by these lines shows the range of Co 2+ −anion bond length for a given Dq.…”