Compositional trends in low-temperature photoluminescence of heavily Er-doped GeS2–Ga2S3 glasses

The influence of temperature and glass composition on the photoluminescence (PL) efficiency of Er3+ ions embedded in (GeS2)100−x(Ga2S3)x (x = 20, 25 and 33 mol%) glasses has been studied. The typical 4f–4f emission bands of Er3+ ions at around 830, 1000 and 1550 nm have been observed in the whole investigated temperature range from 300 K down to 10 K for all the compositions. New 4f–4f luminescence bands, in excess of the three basic ones, have been observed at 670, 870, 1120, 1260 and 1350 nm for (GeS2)75(Ga2S3)25 glass composition, and are tentatively assigned to 2H9/2 → 4I11/2, 4G11/2 → 4F9/2, 2H11/2 → 4I11/2, 4F7/2 → 4I9/2 and 4F3/2 → 4I9/2 transitions, respectively. Thus a considerable influence of GeGaS host composition on the efficiency of 4f–4f transitions of embedded Er3+ ions is documented with the outcome that (GeS2)75Ga2S3)25 composition appears near optimal for the emission efficiency of Er3+ ions. With decreasing temperature the PL efficiency is enhanced considerably with pronounced narrowing of all bands. In the case of the strongest PL band at ~ 1550 nm, corresponding to 4I13/2 → 4I15/2 transition, the narrowing at low temperature is further accompanied by the resolution of well pronounced fine structure due to “crystal field” splitting of corresponding electronic terms. The relationship between the photoluminescence and reflectance spectra as a function of Er content has been discussed.