Precise Manipulation of Discrete Lanthanide Complexes Vitrification via Flexible Chains and Rigid Modules: Accessing Near-Unity Photoluminescence Quantum Yields, Upconversion Luminescence, and Ultra-Bright X-ray Scintillators.

Weakly bonded discrete lanthanide complexes readily decompose on heating, making conventional melt-quenching vitrification extremely difficult. Herein, we design rigid-flexible dual ligands for lanthanide complexes, producing large-area transparent bulk glasses (Btfa-Ln-Glass) with reversible crystalline-glass-glass-ceramic interconversion via "rigid-flexible synergy". Notably, precise rigid-segment conjugation tuning drastically boosts devitrification resistance, yielding stable transparent bulk glasses with ceramization resistance and reversible crystalline-glassy interconversion. The dual-component ligands' flexible segments impart molecular mobility, rigid segments ensure network stability, enabling controllable vitrification. Synchrotron radiation x-ray absorption fine structure (XAFS) analysis confirms that the local coordination geometry, bond lengths, and coordination number of Eu3+ sites in Btfa-Eu-Glass are in excellent agreement with those of the crystalline precursor. After vitrification, the photoluminescence quantum yields (PLQYs) of both Btfa-Eu-Glass and NTA-Eu-Glass increase dramatically to nearly 100%. Furthermore, Btfa-Eu0.5Yb0.5-Glass exhibits pronounced two-photon absorption-mediated upconversion luminescence (UCL) under 980 nm excitation. As the first intrinsic lanthanide complex glass x-ray scintillator, Btfa-Eu-Glass achieves an exceptional light yield of 60,360 ± 273 photons·MeV-1, outperforming all reported lanthanide-doped glass scintillators, and delivers an ultralow limit of detection (LOD) of 124 nGy·s- 1. This work exploits a rigid-flexible balancing strategy to overcome the long-standing challenge of realizing controllable vitrification in discrete lanthanide complexes.