Microstructure and up-conversion luminescence properties of Er3+ and Yb3+ ions co-doped oxyfluoride silicates

Microstructure and up-conversion luminescence properties of Er3+ and Yb3+ co-doped PbF2–ZnF2–SiO2 oxyfluoride silicate were investigated. Up-conversion luminescence spectra consist of four bands centered at 408, 523, 541 and 660 nm which are similar to other Yb3+ and Er3+ co-doped up-conversion materials, but the violet emission near 408 nm accounting to 16.8% in overall intensity is much stronger than others. Another feature is that the change of the ratio of the intensity of the green to red emission is not monotonously. These phenomenon can be explained by micro dendrite crystal appeared in the as cast sample with 0.1 mol% Er3+. The dendrite crystal is identified to be β-PbF2 by X-ray diffraction in which the content of rare-earth ions, Yb3+ and Er3+, is determined to be ∼7.0 mol%. The violet emission near 408 nm of the sample with the concentration of 0.1 mol% Er3+ decreased to 1.6% after the heat treatment because of the diminish of the dendrite.