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

Ge 30 Ga 4 S 65.5 :Er 0.5 glasses with stoichiometric composition have been prepared using a conventional melt-quenching technique. The PL lifetime distribution corresponding to 4 I 13/2 → 4 I 15/2 transition in Er 3+ 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 τ QFRS ≈ 3-4 ms with a half width <3 ms irrespective of PL energy and temperature. The Judd-Ofelt analysis based on optical transitions from 4 I 15/2 level to 4 I 13/2 , 4 I 11/2 , 4 I 9/2, 4 F 9/2, 4 S 3/2, 2 H 11/2 and 4 F 7/2 levels in Er 3+ ions gives the radiative lifetime of 4 I 13/2 → 4 I 15/2 transition τ JO ≈ 2.6 ms. The closeness of τ JO and τ QFRS implies the dominant role of the radiative relaxation in 4 I 13/2 → 4 I 15/2 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 4 I 13/2 → 4 I 15/2 transition has been estimated to be more than 100 times larger than the radiative lifetime.