Vibronic photoexcitation spectra of irradiated spinel MgO·nAl2O3 (n = 2) at low temperatures

•Vibronic photoexcitation band at 230 nm was observed in irradiated spinel at low temperatures for the first time.•Vibronic photoexcitation band shows temperature dependence and becomes obscure at over 120 K.•Huang–Rhys factor S=2.78S=2.78 and Debye temperature, 518 K were estimated from temperature dependence of 230 nm vibronic band.•Defect related Debye temperature was found to be lower than normal mode in MgO · nAl2O3(n = 2).

A vibronic photoexcitation band at approximately 230 nm was found at 13 K in reactor neutron- and electron-irradiated magnesium aluminate spinel (MgO · nAl2O3). Vibronic structure was found to be temperature dependent and became obscure at over 120 K. Huang–Rhys factor S   and Debye temperature ΘDΘD were estimated from the temperature dependence of the 230 nm band by curve-fitting method using Debye approximation. Origin of the vibronic photoexcitation band was suggested as F center.