EPR and photoluminescence studies of ZnO:Mn nanophosphors prepared by solution combustion route

Nanocrystalline ZnO:Mn (0.1 mol%) phosphors have been successfully prepared by self propagating, gas producing solution combustion method. The powder X-ray diffraction of as-formed ZnO:Mn sample shows, hexagonal wurtzite phase with particle size of ∼40 nm. For Mn doped ZnO, the lattice parameters and volume of unit cell (a = 3.23065 Å, c = 5.27563 Å and V = 47.684 (Å)3) are found to be greater than that of undoped ZnO (a = 3.19993 Å, c = 5.22546 Å and V = 46.336 (Å)3). The SEM micrographs reveal that besides the spherical crystals, the powders also contained several voids and pores. The TEM photograph also shows the particles are approximately spherical in nature. The FTIR spectrum shows two peaks at ∼3428 and 1598 cm−1 which are attributed to O–H stretching and H–O–H bending vibration. The PL spectra of ZnO:Mn indicate a strong green emission peak at 526 nm and a weak red emission at 636 nm corresponding to 4T1 → 6A1 transition of Mn2+ ions. The EPR spectrum exhibits fine structure transition which will be split into six hyperfine components due to 55Mn hyperfine coupling giving rise to all 30 allowed transitions. From EPR spectra the spin-Hamiltonian parameters have been evaluated and discussed. The magnitude of the hyperfine splitting (A) constant indicates that there exists a moderately covalent bonding between the Mn2+ ions and the surrounding ligands. The number of spins participating in resonance (N), its paramagnetic susceptibility (χ) have been evaluated.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► ZnO:Mn nanophosphors (∼40 nm) via LSC technique with ODH as a fuel at 300 °C was prepared first time. ► Our method involves easy preparation, low cost, low temperature, and the lack of organic reactants. ► The nanopowders are well characterized by PXRD, SEM, TEM, FTIR, UV–visible, PL and EPR techniques. ► From EPR spectra the spin-Hamiltonian parameters have been evaluated and discussed. ► The spin concentration (N), its paramagnetic susceptibility (χ) have been evaluated.