Self-trapped exciton singlet-triplet splitting in crystals with α-quartz structure: SiO₂, SiO₂-Ge, GeO₂, AlPO₄ and GaPO₄

A fast component of the self-trapped exciton (STE) luminescence was discovered in crystals with α-quartz structure such as SiO₂, SiO₂-Ge, GeO₂, AlPO₄ and GaPO₄, manifesting the singlet-singlet transitions of STEs. Comparison of time resolved photoluminescence (PL) spectra of triplet-singlet transitions and fast singlet-singlet transitions showed the singlet-triplet splitting of STEs in a pure SiO₂α-quartz crystal to be 0.2eV. In other crystals, the singlet-triplet splitting was found to be less than 0.2eV. Small singlet-triplet intervals confirm that electrons of the STE are not confined in one atom's area.