Photoluminescence lifetime spectrum in erbium doped Ge–Ga–S glasses

Ge30Ga4S65.5:Er0.5 glasses with stoichiometric composition have been prepared using a conventional melt-quenching technique. The PL lifetime distribution corresponding to 4I13/2 → 4I15/2 transition in Er3+ ion has been measured experimentally using quadrature frequency-resolved PL spectroscopy (QFRS) from 2 ns to 160 s at room temperature and at 3.7 K. The distribution seems to be principally single-peaked at around τQFRS ≈ 3–4 ms with a half width <3 ms irrespective of PL energy and temperature. The Judd–Ofelt analysis based on optical transitions from 4I15/2 level to 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, 2H11/2 and 4F7/2 levels in Er3+ ions gives the radiative lifetime of 4I13/2 → 4I15/2 transition τJO ≈ 2.6 ms. The closeness of τJO and τQFRS implies the dominant role of the radiative relaxation in 4I13/2 → 4I15/2 transitions. The shape of steady-state PL spectra can be predicted by using a modified McCumber theory taking into account the possibility of absorption and re-emission of PL quanta in heavily doped materials under weak excitation. The latter calculations used Monte Carlo simulations taking into account the re-absorption and re-emission of the PL radiation. The non-radiative lifetime for the 4I13/2 → 4I15/2 transition has been estimated to be more than 100 times larger than the radiative lifetime.