“…Several mechanisms including vapor-liquid-solid, vapor-solid, and oxide-assisted mechanisms [35] have been proposed to explain the growth of 1D solid MgO nanomaterials. Studies on optical properties by photoluminescence were conducted regarding the defects or defect levels in MgO crystals [31][32][33][34], which are associated with oxygen vacancies, Mg vacancies and interstitials. These defects could induce new energy levels within the band gap.…”