Self-trapped excitons in LiB3O5 and Li2B4O7 lithium borates: Time-resolvedlow-temperature luminescence VUV spectroscopy

Results are reported of a coordinated investigation of the dynamics of elec tronic excitations in LiB3O5 and Li2B4O7 crystals by low-temperature lumine scence VUV spectroscopy performed with subnanosecond resolution under synch rotron photoexcitation. Data on the photoluminescence (PL) decay kinetics, time-resolved PL and PL excitation spectra, and reflectance spectra obtaine d at 295 and 9.6 K are reported for the first time; the PL of the borates i n the 3.5-eV region caused by radiative annihilation of self-trapped excito ns (STE) has been established to have an intrinsic nature; the sigma and pi STE luminescence bands originating from singlet and triplet radiative tran sitions have been isolated; the shift of the STE sigma band relative to the pi band has been interpreted; the LBO recombination luminescence band has been isolated; and the creation and decay channels of relaxed and unrelaxed excitons in lithium borates are discussed. (C) 2000 MAIK "Nauka/Interperio dica".