Insights into Nd III to Yb III Energy Transfer and Its Implications in Luminescence Thermometry.

This work challenges the conventional approach of using Nd III 4 F 3/2 lifetime changes for evaluating the experimental Nd III → Yb III energy transfer rate and efficiency. Using near-infrared (NIR) emitting Nd:Yb mixed-metal coordination polymers (CPs), synthesized via solvent-free thermal grinding, we demonstrate that the Nd III [ 2 H 11/2 → 4 I 15/2 ] → Yb III [ 2 F 7/2 → 2 F 5/2 ] pathway, previously overlooked, dominates energy transfer due to superior energy resonance and J -level selection rule compatibility. This finding upends the conventional focus on the Nd III [ 4 F 3/2 → 4 I 11/2 ] → Yb III [ 2 F 7/2 → 2 F 5/2 ] transition pathway. We characterized Nd 0.890 Yb 0.110 (BTC)(H 2 O) 6 as a promising cryogenic NIR thermometry system and employed our novel energy transfer understanding to perform simulations, yielding theoretical thermometric parameters and sensitivities for diverse Nd:Yb ratios. Strikingly, experimental thermometric data closely matched the theoretical predictions, validating our revised model. This novel perspective on Nd III → Yb III energy transfer holds general applicability for the Nd III /Yb III pair, unveiling an important spectroscopic feature with broad implications for energy transfer-driven materials design.