Yb³⁺-doped oxyfluoroborosilicate glasses and glass ceramics containing CaF₂ nanocrystals for 981 nm near infrared fiber lasers

Yb³⁺-doped borosilicate-based glass and glass ceramics containing CaF₂ nanocrystals prepared by conventional melt quench method followed by reheat treatment were characterized for NIR fiber lasers. The crystalline phase, morphology, and the presence of various functional groups were examined through powder X-ray diffraction, scanning electron microscopic, and Fourier transform infrared studies. The fiber drawing nature and the thermal stability were studied through differential scanning calorimetry. The X-ray diffraction and morphology investigations confirm the ceramic behavior of the studied samples with notable transparency. The optical band gap energy was estimated using the absorption spectra. The emission cross-section corresponding to Yb³⁺: ²F_5/2→²F_7/2 (981 nm) transition was determined from the Fuchtbauer–Ladenburg method, Mc Cumber theory, and the emission spectra. Considerably high-emission cross-section and gain coefficient values of glass ceramic obtained by heat treatment at 450 °C/1 h show its suitability to design 981-nm infrared fiber laser sources.