Infrared to Visible Up‐Conversion Emission in Er 3+ / Yb 3+ Codoped Fluoro–Phosphate Glass–Ceramics

Erbium Er 3+ and ytterbium Yb 3+ codoped fluoro‐phosphate glasses belonging to the system NaPO 3 – YF 3 – BaF 2 – CaF 2 have been prepared by the classical melt‐quenching technique. Glasses containing up to 10 wt% of erbium and ytterbium fluorides have been obtained and characterized using differential scanning calorimetry ( DSC ) and UV –visible and near‐infrared spectroscopy. Transparent and homogeneous glass–ceramics have been then reproducibly synthetized by appropriate heat treatment above glass transition temperature of a selected parent glass. Structural investigations of the crystallization performed through X‐ray diffractometry ( XRD ) and scanning electron microscopy ( SEM ) have evidenced the formation of fluorite‐type cubic crystals based during the devitrification process. Finally, infrared to visible up‐conversion emission upon excitation at 975 nm has been studied on the Er 3+ and Yb 3+ codoped glass–ceramics as a function of thermal treatment time. A large enhancement of intensity of the up‐conversion emissions–about 150 times‐ has been observed in the glass–ceramics if compared to the parent glass one, suggesting an incorporation of the rare‐earth ions (REI) into the crystalline phase.