Tuning the micro-structure of germanosilicate glass to control Bi⁰/Bi⁺ and promote efficient Ho³⁺ fluorescence

Bi can exist in a variety of chemical states (with varying ionic charges) and the microstructure of the glass surrounding the ions can be engineered to manipulate the chemical state. In this work, efficient enhancement of Ho3+ emission is observed with the change in local glass environment around Bi by adding Al2O3 to multi-component germanosilicate glass. In this multi-component glass, Al3+ can form tetrahedral AlO4 by accepting the non-bridging oxygen (NBO) and then, the addition of the AlO4-tetrahedron to the glass network facilitates the diffusion of alkali metals. Hence, Al2O3 decreases the Ba2+-rich domain and is conducive to the existence of Bi ions that are at low valence state. Moreover, the emission spectra indicate high efficiency energy transfer (ET) derived from NIR emission centers (Bi0/Bi+) located in close proximity to the Ho3+ ions. These results indicate that the optimized fluorescence of Ho3+ for optical fiber laser can be achieved by adjusting the local structure of the host glass.