الفهرس 
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Abstract
Er3+/Yb3+ co-doped potassium-lead-germanate (70geo2–20pbo–10K2O) glasses with a fixed Er3+ concentration (0.5 mol.%) and different Yb3+ concentrations (0, 0.5, 1.5, and 2.5 mol.%), have been synthesized by the conventional melting and quenching method. The amorphous nature of the prepared glasses has been confirmed by the x-ray diffraction. The structure and vibrational modes of the glass network were investigated by the infrared absorption and Raman spectroscopy. Raman spectrum of the undoped glass sample indicates that the maximum phonon energy of the glass network is around 811 cm-1. The thermal behavior of all glass samples was investigated by the differential thermal analysis, and it was found that the thermal stability of the glasses obviously improves with increasing of Yb3+ concentration. The temperature dependence of the electrical conductivity at a constant applied voltage, were measured for all glasses and it was found that with increasing of Yb3+ concentration, the activation energy for the DC conduction increases, while the DC conductivity decreases.Optical absorption measurements show that the absorption intensity at around 976 nm increases linearly with Yb3+ concentration. Infrared-to-visible frequency upconversion process was investigated in all glasses. Intense green and red upconversion emission bands centered at around 532, 546, and 655 nm were observed, under excitation at 980 nm of diode laser at room temperature. The quadratic dependence of these emissions on the excitation power indicates that a two-photon upconversion process occurs under excitation of 980 nm. It was found that the upconversion emission intensity increases obviously with increasing of Yb3+ concentration. This enhancement is attributed to the efficient energy transfer from Yb3+ to Er3+ ions. Similar visible (intense green and very week red) emissions were also observed under excitation at 488 nm of Ar+ laser.