On-Demand Vitrification of Multicomponent Lanthanide Complexes for Magnetism and Up-Conversion Emission

Molecule-based glassy systems and their solid solutions emerge as advanced optical materials that circumvent the inherent limitations of inorganic and polymer glasses such as energy-intensive synthesis and stringent processing requirements. This work presents rationally designed discrete lanthanide complexes [Ln(dbm)₃(C₄PO)] (dbm= dibenzoylmethane, C₄PO = tri-n-butylphosphine oxide) demonstrating an unprecedented reversible "crystal (1-Ln) → liquid → glass (1-Ln-Q) → glass-ceramic (1-Ln-H) → crystal" phase transition cycle, featuring the melting points of around 130 °C alongside the glass transition temperatures of approximately 20 °C. Our molecular engineering strategy provides an opportunity to achieve dual functional breakthroughs in magnetism and up-conversion (UC) emission while reducing the thermal budget. By integrating the glass transition into single-molecule magnets, we enable mild thermal processing that converts crystalline 1-Dy architectures into deformable glassy 1-Dy-Q phases. Subsequent structural evolution realizes a 96.9% reversible recovery of dynamic magnetism in reconstructed 1-Dy-H. Solid solution engineering through controlled eutectic/glass transitions produces composition-tunable materials 1-Yb/1-Eu, 1-Yb/1-Sm, and 1-Y/1-Yb/1-Pr, and 1-Yb/1-Eu achieves a quantum yield of UC emission values up to 3.07 × 10⁻⁵% under 980 nm irradiation comparable to conventional solution-processed benchmarks. This study establishes a paradigm for developing molecule-based solid solutions in lanthanide photonics, synergistically preserving intrinsic optical merits while enabling phase-programmable functionality and sustainable device fabrication.