Effect of OH- on fluorescence properties in 1.5-1.6 μm for Er:Yb:YCOB crystal

FTIR absorption spectra indicate that H+ can easily enter the crystal structure and form OH- centers in Er:Yb:YCOB and O-H bonds prefer to lie in the a-c plane. Within our current studied concentration level, crystal samples with higher OH- absorption coefficients demonstrate stronger fluorescence intensity and longer fluorescence lifetime at 1535 nm. As the stretching vibration energy of OH- group approximately corresponds to the energy gap between the I-4(11/2) and I-4(13/2) levels of Er3+, and thus, OH(- )ions can shorten the fluorescence lifetime of Er3- -I-4(11/2) level by the phonon-assisted cross-relaxation process between the Er3+ and OH- ions. Our current results confirm that a certain content of OH- ions can enhance the energy transfer process from Yb3+ to Er3+ and subsequently promote fluorescence output in 1.5-1.6 mu m. (C) 2019 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.