Observation of a new photoluminescence band at 320 nm under 270 nm excitation in Ge-doped silica glass

We investigate the influence of temperature on photoluminescence (PL) in Ge-doped silica glass. Under 270 nm excitation, we observe only one PL band at 424 nm at room temperature (RT). This band shifts to 436 nm with cooling (4 K), and a new PL band is recorded at 320 nm. We assign these PL bands to triplet-to-singlet and singlet-to-singlet transitions of a same Ge-related defect, whose structure is still unknown. The shift of the PL band (from 424 nm at RT to 436 nm at 4 K) is explained by the decrease of the overlap between PLs from different centers.