Origin of 2.7 μm luminescence and energy transfer process of Er3+: 4I11/2→4I13/2 transition in Er3+/Yb3+ doped germanate glasses

An investigation of spectroscopic property and energy transfer process of Er3+ doped and Er3+/Yb3+ co-doped germanate glasses is presented. The emission cross section of the 4I11/2 → 4I13/2 transition of Er3+ doped germanate glass is calculated to be 1.2 × 10−20 cm2. The microparameter of energy transfer from Yb3+:2 F5/2 to Er3+:4I11/2 is calculated to be 2.74 × 10−39 cm6/s, and that is not phonon dependent in the quasiresonant process. The intensity of the emission around 2.7 μm is enhanced obviously when Er3+ co-doped with Yb3+. The excited-state relaxation process of Er3+ is adequately described by a combination of the Judd-Ofelt model and the energy-gap law. With the exception of 4I13/2 and 4I11/2 levels, multiphonon relaxation is dominant for all excited states, making it possible to efficiently pump the 1.55 μm 4I13/2 → 4I15/2 and 2.7 μm 4I13/2 → 4I11/2 emission by excitation of Yb3+:2F5/2 and Er3+:4I11/2 at 980 nm.