Enhanced upconversion emission in crystallization-controllable glass-ceramic fiber containing Yb³⁺-Er³⁺ codoped CaF₂ nanocrystals

Functional nanocrystal-containing materials have been a hot topic in recent years. However, few researches have focused on functional nanocrystals contained in optical glass fibers. In this research, transparent CaF₂ glass-ceramic was prepared by a melt-quenching method. Greatly enhanced upconversion luminescence was observed after heat treatment. By applying a novel method called melt-in-tube, precursor fiber free of crystals was fabricated at the drawing temperature where the clad was softened while the core was melted. Glass-ceramic fiber with fiber core containing Yb³⁺-Er³⁺ codoped CaF₂ nanocrystals was obtained after heat treatment at a relatively low temperature. Electron probe micro-analyzer measurement shows no obvious element diffusion between the core and clad. Greatly enhanced upconversion emission was detected in the glass-ceramic fiber excited by a 980 nm laser, suggesting the developed glass-ceramic fiber is a promising material for upconversion laser. (paper)