PHOTOLUMINESCENCE AND EXCITATION SPECTROSCOPY OF ER-DOPED AS2S3 GLASS - NOVEL BROAD-BAND EXCITATION MECHANISM

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, 4I 13/2→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 Ge33As12Se 55 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 Er 3+ 4f shells. Microscopic characterization techniques reveal that the Er2S3-doped glasses also contain residual Er 2S3 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. © 1995 American Institute of Physics.