Boosted Continuous‐Wave Upconversion Microlaser Based on Yb 3 ⁺/Ho 3 ⁺ Co‐Doped Oxyfluoride Glass‐Ceramics with NaYF₄ Nanocrystals

Abstract Achieving low‐threshold, high‐efficiency microlasers remains a significant challenge. Recent advancements in oxyfluoride glass ceramics (GCs), where rare earth (RE) ions are embedded in fluoride nanocrystals within a glass matrix, offer both enhanced luminescence and superior processability compared to traditional RE‐doped materials. In this study, the use of NaYF₄: Ho 3 ⁺, Yb 3 ⁺ oxyfluoride GCs in microlaser applications is investigated. Micro‐area energy dispersive spectroscopy analysis further verified the enrichment of RE ions within the fluoride nanocrystals. The up‐conversion luminescence of Ho 3 ⁺ is significantly enhanced, with notable emissions at 540 and 750 nm—features not observed in the precursor glass. Moreover, the fabricated whispering gallery mode GC microcavity exhibited a two‐order magnitude increase in up‐conversion laser intensity and extremely low thresholds (1.18 µW at 540 nm, 0.89 µW at 650 nm, and 1.5 µW at 750 nm). For the first time, simultaneous multi‐band up‐conversion laser output from Ho 3 ⁺ ions is achieved in the GC microcavity. The oxyfluoride GC formulation also significantly enhanced the up‐conversion fluorescence of Er 3 ⁺ ions, with a laser output ≈36 times greater than that of the precursor glass microcavity. These results highlight the potential of RE‐doped oxyfluoride GCs for low‐threshold microlasers in photonics and biomedical applications.