i. The color of the ruby stones was modified by high temperature metal oxide treatment. The surface color of the ruby changes from pinkish blue (after acid treatment) to deep red and light pink color after heat treatment using PbO and ZnO, respectively.The DRS-UV–vis absorption spectra confirm the observed color.
ii. The density values of the as-received samples do not change after heat treatment (3.9–4.0), hence can fetch accepted market value.
iii. XRD and PL data confirm the presence of -Al2O3 phase in the ruby while trace of Cr content was detected from the XPS.
iv. The information regarding chemical and crystallographic environment was obtained from the Al 2p high resolution spectra.High resolution Al 2p scan shows shift in binding energy of the metal oxide treated samples with respect to the acid treated sample. However, the ZnO treated sample shows a −ve binding energy shift in contrast to PbO treated one that shows +ve binding energy shift. This observation confirmed the change in the chemical environment of the Al ions in the ruby matrix during high temperature metal oxide treatment.
v. The peak separation between R1 and R2-lines in photoluminescence spectrum of the lead oxide treated sample are explained on the basis of ionic substitution of the Pb2+ and Pb4+ ion in Al3+which is supported by XRD and XPS analysis.
vi. The change in surface appearance and chemistry of the ruby stones after PbO treatment is explained based on the ionic substitution of the Al3+ by Pb ions and alteration in the O co-ordination (by creating reducing atmosphere). On the contrary,the surface change in the ZnO treated sample is due to the stress and the alteration in O co-ordination (by creating oxidizing atmosphere). The XRD, XPS, Raman and photoluminescence studies confirmed the above observation. The attribution of the Lorenzian and Gaussian profile fitting in the photolumine scencespectra and the EDS spectra further support the above observations.