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 [²H_11/2 → ⁴I_15/2] → Yb^III [²F_7/2 → ²F_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 [⁴F_3/2 → ⁴I_11/2] → Yb^III [²F_7/2 → ²F_5/2] transition pathway. We characterized Nd_0.890Yb_0.110(BTC)(H₂O)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.