Oxyfluoride glass–ceramic fibers doped with Nd3+: structural and optical characterization

Abstract

Transparent oxyfluoride glass–ceramic fibers containing LaF₃ nanocrystals have been drawn using a single crucible method and crystallization after an appropriate heat treatment. Optical fibers have been obtained a posteriori through the deposition of SiO₂ cladding prepared by sol–gel and deposited by dip-coating. Detailed thermal and structural characterization performed by DTA, XRD, HRTEM and SAXS showed the good reproducibility of the technology. Phase separation, due to fluorine immiscibility in an oxide glass matrix, initiates the crystallization. The crystallization mechanism is a diffusion-controlled process and the local compositional changes of the glass matrix around the nanocrystals limit the crystal size to 10–20 nm depending on the treatment conditions. The optical characterization demonstrated the light propagation into the glass–ceramic core and the possibility to selectively excite Nd³⁺ ions in the fluoride nanocrystals with a corresponding increase of the luminescence efficiency.