Abstract
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.