Optical and FTIR structural studies on CoO-doped strontium phosphate glasses

Glass samples in the system (60-x)P2O5-40SrO-xCoO ((0.0 <= x <= 0.6) mol%) were successfully prepared via melt-annealing route. X-ray diffraction (XRD) data reveal the amorphous nature of examined glasses. A strong absorption band is appeared in all glass samples (pure & doped) in the UV region. This band is considered due to the trace iron impurities that exist within the raw materials used to prepare these samples. Additional absorption bands were appeared in the optical absorption spectra and considered as a result of adding CoO with different concentrations (0.025, 0.05, 0.1, 0.2, 0.4, 0.6 mol%), indicating that the divalent cobalt ions (Co2+) exist in the two coordination states (octahedral and tetrahedral) in this glass system. Optical band gap energy, E-opt was calculated and found to be in the range of 3.94-3.5 eV. E-opt decreases as the amount of CoO increases. FT-IR experimental data reveal IR vibrational bands that are featured to the specific structural building units related to the phosphate matrix. The addition of cobalt oxide with small doping quantities together with the presence of cobalt ions in structural modifying sites causes slight variations in the IR spectra.