Luminescence of the B2Σ+-X2Σ+ band system of AlO during plasma electrolytic oxidation of aluminum

Highlights: → Plasma electrolytic oxidation (PEO) of aluminum in citric acid. → Luminescence of the B2Σ+-X2Σ+ band system of AlO during PEO. → The measured intensity distributions are employed to estimate the mean plasma temperature. → The composition of plasma containing aluminum and oxygen is calculated. - Abstract: Two broad luminescence peaks with clearly pronounced structure, extending from roughly 18,200 to 18,800 cm-1 and from 19,000 to 19,700 cm-1 with the maxima at approximately 18,500 and 19,500 cm-1, respectively, are obtained during plasma electrolytic oxidation of aluminum. They are assigned to the v'-v'' = -1 and -2 band sequences of the B2Σ+-X2Σ+ emission transition of AlO. The measured intensity distributions are employed to estimate the population of vibrational levels of the upper electronic state, and consequently the mean plasma temperature. The composition of plasma containing aluminum and oxygen under assumption of thermodynamic equilibrium is calculated in the temperature up to 11,000 K in order to explain the appearance of the observed spectral features.