# Spectroscopic investigations of $Mn^{2+}$ ions doped polyvinylalcohol films

Kumar, Hemantha GN and Rao, Lakshmana J and Gopal, NO and Narasimhulu, KV and Chakradhar, RPS and Rajulu, Varada A (2004) Spectroscopic investigations of $Mn^{2+}$ ions doped polyvinylalcohol films. In: Polymer, 45 (16). pp. 5407-5415.

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Electron paramagnetic resonance (EPR), luminescence and infrared spectral studies have been carried out on $Mn^{2+}$ ions doped in polyvinylalcohol (PVA) films. The EPR spectra at room temperature exhibit sextet hyperfine structure (HFS), centered at $g_{eff} \approx 2.0$ characteristic of Mn2+ ions in octahedral symmetry. The zero-field splitting parameter (D) at room temperature has been evaluated from the intensities of allowed hyperfine lines. The EPR spectra exhibit a marked concentration dependence. The EPR spectra have also been recorded at various temperatures. The number of spins participating in the resonance is measured as a function of temperature and the activation energy $(E_a)$ is calculated. The paramagnetic susceptibility (\chi ) is calculated from the EPR data at various temperatures. From the plot of $1/ \chi$ versus T, the Curie constant and Curie temperature have been evaluated. The emission spectrum of Mn2+ ions doped PVA film exhibits three bands centered at 390, 448 and 465 nm. The band at 448 nm is attributed to $^4T_{1g} \rightarrow ^6A_{1g}$ transition of $Mn^{2+}$ ions. The bands at 390 and 465 nm are attributed to the recombination of free charge carriers. The excitation spectrum exhibits two bands at 250 and 216 nm, which are attributed to host lattice absorption bands. The FT-IR spectrum exhibits few bands, which are attributed to $O-H$, $C-H$, $C=C$ and $C-O$ groups of stretching and bending vibrations.