Supplementary Information
Competing effects between intrinsic and extrinsic defects in pure and Mn-doped ZnO nanocrystals
Thomas Rufa, Sergej Reppa, Joanna Urbana, Ralf Thomannb, Emre Erdema,*
a Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstraße 21, 79104 Freiburg, Germany
b Freiburger Materialforschungszentrum (FMF), Albert-Ludwigs-Universität Freiburg, Stefan-Meier-Straße 21, 79104 Freiburg, Germany
*corresponding author:
Synthesis:
Figure 1: Flow chart for the synthesis of Zn1-xMnxO nano particles.
FTIR analysis:
Figure 2:FTIR spectra of a set of air dried Zn1-xMnxO.
Figure 3: FTIR spectra of a set of air dried Zn1-xMnxO; signals marked with * are just found in undoped nano ZnO.
Table 1: Assignment of signals in FTIR spectra of nano Zn1-xMnxO, “y” assigns the observed signal, “n” assigns the not observed signal; signals marked with * are only found in undoped nano ZnO
[cm-1] / TR1a
x= 0 / TR4a
x= 0.001 / TR6a
x= 0.01 / TR8a
x= 0.03 / Assignments
~ 3370-3380 / y / y / y / y / OH-stretching
(H2O and acetate)
~1570 / y / y / y / y / C=O-stretching (acetate)
~1504* / y / n / n / n / shifted C=O-stretching
~1387 / y / y / y / y / OH-bending (acetate or H2O) or C-O stretching (acetate)
~1338 / y / y / y / y / shifted
~1045 / y / y / y / y / C-O stretching combined with C-O beding (acetate)
~1018 / y / y / y / y
~930 / y / y / y / y / Zn-O stretching 1
~831 / y / n / y / y / epoxide-group 2
~738* / y / n / n / n / Cluster Zn-O-C Relationship with other phase
~706* / y / n / n / n
~674 / y / y / y / y / Zn-O stretching 1
~614 / y / y / y / y / Zn-O stretching 3; Note that, the reference is about ZnO/Mn3O4 nanocomposites
The typical IR vibration modes changes with concentration of manganese.
Table 2: Shift of typical Zn-O strectching vibration with changing Mn concentration.
TR1ax = 0 / TR4a
x = 0.001 / TR6a
x = 0.01 / TR8a
x= 0.03
457 cm-1 / - / 446 cm-1 / 435 cm-1
UV-Vis analysis:
The optical properties of undoped ZnO and Mn-doped ZnO nanoparticles were studied UV-Vis diffuse reflectance spectra. To obtain the optical band gap of samples from reflection spectra according to Tauc method 4, a graph between (αhυ)2 versus photon energy (hυ) is plotted and given in Fig. 4-9. The absorption coefficient α is determined the following Eq. (1),
(1)
where Rmax is value of the maximum reflectance, Rmin is value of the minimum reflectance and R is the reflectance values. The intercept of this plot on the energy axis determines the optical band gap of undoped and Mn-doped ZnO nanoparticles. The optical band gap of undoped ZnO and MnO-doped ZnO ceramics is obtained and given in the inset of each figures.
Figure 4: Tauc-plot for nano ZnO.
Figure 5: Tauc-plot for nano Zn1-xMnxO (x = 0.000005).
Figure 6: Tauc-plot for nano Zn1-xMnxO (x = 0.00001).
Figure 7: Tauc-plot for nano Zn1-xMnxO (x = 0.0001).
Figure 8: Tauc-plot for nano Zn1-xMnxO (x = 0.001).
Figure 6: Tauc-plot for nano Zn1-xMnxO (x = 0.01).
Figure 9: Tauc-plot for nano Zn1-xMnxO (x = 0.03).
TEM analysis:
Figure 10: TEM picture of annealed Zn1-xMnxO (x = 0.03). Particle size of annealed Zn1-xMnxO (x = 0.03): (18.55 ± 3.64) nm.
Further EPR analysis:
Figure 11: Correlation between Hyperfine constant A and manganese concentration.
Figure 12: Correlation between zero field splitting and manganese concentration
Figure 11 and 12 are extracted from the EPR spectra. Hyperfine parameter (Fig.11) and magnetic field difference between the lowest and the highest Mn-lines (which is proportional to ZFS parameter, Fig.12 inset) were plotted by increasing the Mn concentration. Both parameters A and DB (hence, ZFS) show systematic increase and decrease by increasing Mn concentration, respectively. For the simulation of the spectra of isolated Mn2+-ions, the program Easyspin implemented in MATLAB® was used. The simulation (Fig. 13) provides information on spin-Hamiltonian parameters, such as the g-factor, the hyperfine parameter A and zero field splitting (ZFS) parameter D. Following table (3) summarizes the extracted parameters:
Table 3: Spin-Hamiltonian parameters derived from simulation for TR5
Parameters / Valueg-factor / (1.996, 1.997, 1.998) / a.u.
D (ZFS) / 720 / MHz
A (hyperfine) / (220, 220, 221) / MHz
A slight anisotropy in the g-factor and the hyperfine coupling constant A were detected via simulation. This is indicated, as the wurtzite structure is hexagonal. Additionally, it is confirmed that there is only one Mn2+ center in a specific magnetic surrounding.
Figure 13: Simulated and experimental spectra of annealed TR5 (x = 0.001).
References:
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4 S. Mahanty, D. Basak, J. M. Merino, and M. Leon, Materials Science and Engineering B-Solid State Materials for Advanced Technology 68, 72 (1999).