Composition dependent frequency upconversion luminescence in Er-doped oxychloride germanate glasses

Er³⁺-doped oxychloride germanate glasses have been synthesized by conventional melting and quenching method. Structural and thermal stability properties were obtained based on the Raman spectra and differential thermal analysis, indicating that PbCl₂ plays an important role in the formation of glass network and has an important influence on the maximum phonon energy and thermal stability of host glasses. Intense green and red emissions centered at 525, 546, and 657 nm, corresponding to the transitions ²H_11/2→⁴I_15/2, ⁴S_3/2→⁴I_15/2, and ⁴F_9/2→⁴I_15/2, respectively, were observed at room temperature. With increasing PbCl₂ content, the intensity of green (525 and 546 nm) emissions increases significantly, while the red (657 nm) emission increases slowly. The results indicate that PbCl₂ has more influence on the green emissions than the red emission in oxychloride germanate glasses. The possible upconversion luminescence mechanisms has also been estimated and discussed.