Effect of Mn doping on the structural and optical properties of sol-gel derived ZnO nanoparticles

Abstract

Abstract:Un-doped and Mn-doped ZnO nanoparticles were successfully synthesized in an ethanolic solution by using a sol-gel method. Material properties of the samples dependence on preparation conditions and Mn concentrations were investigated while other parameters were controlled to ensure reproducibility. It was observed that the structural properties, particle size, band gap, photoluminescence intensity and wavelength of maximum intensity were influenced by the amount of Mn ions present in the precursor. The XRD spectra for ZnO nanoparticles show the entire peaks corresponding to the various planes of wurtzite ZnO, indicating a single phase. The diffraction peaks of doped samples are slightly shifted to lower angles with an increase in the Mn ion concentration, signifying the expansion of the lattice constants and increase in the band gap of ZnO. All the samples show the absorption in the visible region. The absorbance spectra show that the excitonic absorption peak shifts towards the lower wavelength side with the Mn-doped ZnO nanoparticles. The PL spectra of undoped ZnO consist of UV emission at 388 nm and broad visible emission at 560 nm with varying relative peak intensities. The doping of ZnO with Mn quenches significantly the green emission while UV luminescence is slightly affected. 78.55.-m; 78.67.-n PACS (2008):

Solubility of Mn in ZnO Nanocrystallites using Wet Chemical Synthesis

“…Substitution of Mn for Zn 2+ requires local expansion or contraction of the lattice to accommodate the manganese ion due to ionic radii differences. Since Mn can exist as Mn 2+ , Mn 3+ and Mn 4+ (respective ionic radii are 0.83Å, 0.65Å and 0.53Å), one cannot be certain of the actual distribution of Mn in the lattice [22], [23]. If Mn 2+ ion of greater ionic radius substitutes Zn 2+ (0.74 Å), the peaks will shift towards the lower angles because of increase in d-spacing due to substitution of lattice site by ion of higher radius.…”

Solubility of Mn in ZnO Crystallites Synthesized Using Solid State Techniques

“…It is important to note that, adversely, excessive Mn doping encouraged spinel formation such as ZnMnO3 and ZnMn3O7 that could lead to poor non-linearity. However, during heating, the solubility of Mn ions could increase because of Mn 2+ reduction to Mn 3+ The presence of the additional secondary phases as indicated by these peaks is thought to be the result of manganese acetate residue in the sample (and is probably in the form MnO, MnO2, Mn2O3 or Mn3O4) [23][24][25]. The absence of the impurity peaks implies that the percentage doping employed is within the solubility limits of Mn in ZnO with respect to the corresponding temperature.…”

Zinc Oxide Nanoparticles and Photodynamic Therapy for the Treatment of B-chronic Lymphocytic Leukemia

“…The emission spectra of all these NPs had one weak band in the UV region around 397 nm that could be attributed to their band gap as well as another broad one at 542 nm in the visible region, which could be related to oxygen defects. The visible emission is the dominant feature of the luminescence of ZnO and Mn-doped ZnO NPs and results from recombination involving trap states [92]. This increase of fluorescence intensity probably indicates that the incorporation of Mn ions into ZnO NPs may suppress some nonradioactive recombinations of free excitation that is near the band gap emission [92].…”

“…The visible emission is the dominant feature of the luminescence of ZnO and Mn-doped ZnO NPs and results from recombination involving trap states [92]. This increase of fluorescence intensity probably indicates that the incorporation of Mn ions into ZnO NPs may suppress some nonradioactive recombinations of free excitation that is near the band gap emission [92].…”

“…An FTIR spectrum of ZnO NPs showed an absorption band centered at 451 cm -1 corresponding to the stretching vibration of Zn-O, confirming the formation of a ZnO bound [53,93], and a vibration band at 1021 corresponding to a C-O bond. The O-H broad stretching band at 3438 cm -1 is shown in the spectrum [92,94]. The intense absorption bands at 1405 cm -1 and 1586 cm -1 were due to C-C and CH 3 COOstretching vibrations of carboxylic acid, respectively [95].…”