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.