The comparative core level Cr 2p spectra are shown in Fig. 3h. In case of acid treated and PbO treated sample trace content of Cris observed (hump like feature in Fig. 3h-i and 3h-ii) in the binding energy range of 570–600 eV. However, a small discrepancy is observed in case of ZnO treated sample (Fig. 3h-iii). The core level spectrum of Cr 2p (shown in Fig. 3h-iii), showing two peaks located at 576.5 eV and 585.5 eV, are assigned to Cr 2p3/2and Cr 2p1/2,respectively [24,25]. This type of Cr 2p and O1s peak shift was observed in Cr doped ZnO system by Lee et al. [26]. These Cr 2p3/2 and Cr 2p1/2 peaks are deconvolute in to its sub peaks and presented in Fig. 3i which indicated the Cr ions multivalent electron affinity towards the oxygen.This result implies that the local chemical state of Al 2p and O1s are influenced by Pb4+ and Zn2+ incorporation into the lattice of ruby. In case of PbO treated sample there occurs a negative binding energy shift in the Al 2p peak where as a positive binding energy shift was observed in case of ZnO treated sample. To achieve the charge balance in (in case of PbO treated sample) the Al2O3 lattice, a trace of lead ions may transform to lower valence by gaining the electrons from Al3+ ions. This leads to a reducing environment in alumina matrix which resulted in the XPS peak shift to low binding energy site. However, in case of ZnO treated sample, the Zn2+ ions diffuse into the Al2O3 lattice and the ionic balance was achieved by exchange of electron between the Zn2+ and Al3+ions. The Al3+ ions withdraw one electron from the Zn2+ ions creating an oxidizing environment in the alumina matrix which shifts the Al 2p peak to higher binding energy. Similar, type of shift in Al 2p peak position was reported by Strohmeier [27] for the ZnAl3O4 compound. By observing the Al 2p, Cr 2p and O1s peaks in ZnO treated ruby sample, it is suggested that two separate shallow phases i.e. ZnAl2O3 and ZnCr2O6[27] might have formed on the surface.