Up-conversion luminescence efficiency in Er-doped chalcogenide glasses

Abstract

The efficiency of up-conversion luminescence of Er3+ ions (excited by laser light operating at 810 nm) in the GeS2–Ga2S3:Er2S3 system strongly depends on the energy position of the fundamental absorption edge. This dependence is due to non-radiative energy exchange between the electronic subsystem of the glassy matrix and excited levels of Er3+ ions. In chalcogenide glasses Ge and Ga atoms are fourfold coordinated. Except for the M (M=Ge, Ga)–S heterobonds, the rest are M–M homobonds. These homobonds can be detected with Raman spectroscopy. The energy position of the absorption tail of the fundamental band depends on the concentration of M–M homobonds. When the concentration of these bonds increases the absorption edge shifts to longer wavelengths and the intensity of up-conversion luminescence decreases. The relative concentration of M–M bonds depends not only on composition of the glassy matrix but also on the synthesis and on concentration of extrinsic impurities such as OH−, SH− and –CH2–. Another cause of reduction of up-conversion luminescence intensity is the inhomogeneous distribution of REI in the Ga2S3–GeS2 glasses. The simple model describing dependence of luminescence intensity on type of REI distribution in the glassy matrix is discussed.