Self-trapped exciton in Li₂GeO₃

Self-trapped excitons (STE) are discovered in Li₂GeO₃ crystal. The PL band at 2.7 eV with a strong Stoke's shift is excited in the intrinsic absorption range of Li₂GeO₃ crystal, in which the optical gap is situated at 6 eV. The activation energy of the STE luminescence thermal quenching is not monoenergetic and is situated in the range 40-100 meV. The luminescence is strongly polarized. The decay kinetics can be characterized by τ = 0.9 ms at 45 K. At 5 K it can be approximated by fast (0.6 ms) and slow (4-2.5 ms) components. Decay kinetics is determined by triplet state of STE splits in zero magnetic field. Two different excited triplet states (centers) have the average ODMR parameters [D] = 6.3 GHz and [E] = 0.6 GHz. The transient absorption of STE shows two bands at 3.7 and 4.7 eV, similar to transient absorption of STE in GeO₂ crystal with the structure of α-quartz.