Identification of free and bound exciton emission of MgO single crystal in vacuum ultraviolet spectral range

Temperature dependencies of optical reflectance and cathodoluminescence (CL) spectra were measured for the MgO single crystal using a custom-built vacuum ultraviolet (VUV) spectroscopic system. Simultaneous observation enabled us to identify free exciton (FE) and bound exciton (BE) emissions by comparing the CL emission with the exciton resonance structures. The results indicated that the BE emission dominates the near-band edge emission, and the FE emission was observed as a shoulder at 300 K. The results ensure strong excitonic nature and potential of a rock salt-structured MgO-based material system for an active element in the VUV light emitter.