Two-Dimensional Mapping of Er3+ Photoluminescence in CaF2 Crystal Lines Patterned by Lasers in Oxyfluoride Glass

The laser-induced crystallization method is applied to an oxyfluoride glass with the composition of 41.5SiO₂–21.3Al₂O₃–4.8CaO–12.6NaF–16.4CaF₂–2.9NiO–0.5ErF₃ (mol%), and the lines consisting of CaF₂ nanocrystals (diameter: ～20 nm) are patterned on the glass surface. It is found from micro-photoluminescence (PL) spectra of Er³⁺ ions that Er³⁺ ions are incorporated into CaF₂ nanocrystals formed by laser (continuous-wave Yb:YVO₄ fiber laser with a wavelength of 1080 nm) irradiations. Two-dimensional mappings of the PL intensity for the ⁴S_3/2→⁴I_15/2 transition of Er³⁺ ions are measured for the surface and cross section of the patterned lines. It is found that two phases giving different PL intensities are formed in the laser-irradiated region, suggesting that the center part of the laser-irradiated region consists of Er³⁺-doped CaF₂ nanocrystals and the surrounding of the center part gives the fluoride ion rich coordination state for Er³⁺ ions. The formation mechanism of Er³⁺-doped CaF₂ nanocrystals is related to the temperature distribution of the laser-irradiated region.