Photoluminescence and excitation spectroscopy of Er-doped As2S3 glass: Novel broad band excitation mechanism

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Abstract
Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy carried out on bulk samples of Er:As2S3 glasses demonstrate that Er3+ is incorporated in optically active sites in the glass and gives rise to a broad ∼1500–1600 nm, 4I13/2→4I15/2 emission spectrum similar to those observed in Er‐doped oxide glasses. In addition to the expected 980 nm (4I15/2→4I11/2) Er3+ PLE band, the 1500–1600 nm Er3+ PL band in the glass exhibits a remarkably broad PLE spectrum which extends from the As2S3 Urbach absorption edge at ∼550 nm to beyond 1000 nm. This broad PLE band corresponds closely to an exponential PLE band observed in the ‘‘band tail’’ spectral range for Er‐doped Ge33As12Se55 glasses. These unusual PLE spectra indicate that in Er‐doped chalcogenide glasses there is an additional broad‐band, below gap, extrinsic absorption mechanism which efficiently excites the characteristic 1550 nm, 4I13/2→4I15/2 Er3+ emission band. It is not possible to determine at present whether the Er dopants themselves are responsible for the broad band absorption which excites the Er3+ PL bands, or if photoexcited carriers attributable to absorption by other impurities transfer their energy to the excited states of the Er3+ 4f shells. Microscopic characterization techniques reveal that the Er2S3‐doped glasses also contain residual Er2S3 crystallites which give rise to sharp, narrow line 1550, 980, and 810 nm Er3+ optical spectra characteristic of polycrystalline Er2S3. The temperature dependence of the Er2S3 PL and PLE spectra enables the energy levels of the 4I13/2 excited state and 4I15/2 ground state manifolds to be determined.