A time-resolved luminescence spectroscopy study of non-linear optical crystals K2Al2B2O7

► Charge-transfer absorptions from O2− to Fe+ were revealed at 4.7, 5.8 and 6.5 eV. ► From reflection spectrum at 7 K the bandgap Eg was estimated as 7.8-8.2 eV. ► Intrinsic PL at 3.28 eV originates from annihilation of self-trapped exciton. ► Strong PL band at 1.72 eV originates from a radiative transition in Fe3+ ion. ► PL bands at 2.68 and 3.54 eV originate from Fe3+ associated with lattice defects.