XRD profiles of pure MnO2 and Mn doped NiO are shown in Fig 1 . The peak around 2θ =29 o remains for all the Mn doped NiO samples with a reduced intensity. Although we started with MnO2 where Mn has an oxidation state of Mn +2 , other oxidation states like Mn +3 , Mn +4 can also co-exist. Some of the XRD parameters of the different Mn oxides are given in Table . Although the list is not complete, it can give us a direction in analyzing the results. The peak at 2θ =29 o mentioned above seems to be due to formation of Mn3O4 which is basically (Mn +2 ) tet -(Mn +3 2) oct O4 spinel structure with Mn +2 at the tetrahedral sites and Mn +3 at the octahedral sites. Some papers have also reported this peak due to (310) peak of MnO2. . The crystallite size for NiO was 30 nm obtained from Scherer equation. The crystallite size of the Mn doped NiO samples were also determined by Gaussian fit. For 1% Mn doped NiO, the crystallite size was 44 nm for the most intense peaks. The lower intensity peaks showed a particle size around 6 nm around 38 O and 13 nm around 44 O which were due to NiO . The results obtained from XRD and optical characterizations performed later are given in Table Increasing the Mn percentage to 3% caused a drastic reduction in crystallite size with small NiO crystallites of 1 nm. The Mn oxide crystallites were of the size of 10 nm.