Luminescence of singlet self-trapped excitons in MgF2

Fast (tau~1.7 ns) broadband (full width at half-maximum = 1.1 eV) vacuum ultraviolet (VUV; hnu = 8.4 eV) luminescence from MgF2 crystals has been detected at low temperature (T < 80 K) and analyzed with techniques of cathodoluminescence and time-resolved VUV spectroscopy using synchrotron radiation. The VUV emission discovered has been attributed to the luminescence of spin-singlet self-trapped excitons (STEs). In contrast to the case for alkaline earth fluoride crystals with fluorite structure, the luminescence of the singlet STEs in MgF2 shows smaller Stokes shift than that of the triplet STEs, which is similar to 'typical' behavior observed for alkali halide crystals.