Triple-readout luminescence thermometry in a heterodinuclear Yb–Er complex and performance comparison with the homodinuclear analogues

Abstract

This work reports the thermometric properties of a heterodinuclear Yb–Er complex, [{Yb(tta)₃}(µ²-bpm){Er(tta)₃}] (1) (tta⁻ = thenoyltrifluoroacetonate and bpm = 2,2'-bipyrimidine), together with the corresponding homodinuclear analogues [{Ln(tta)₃}₂(µ²-bpm)] (Ln = Yb(2), Er(3)). Under 394 nm excitation, complex 1 enables temperature sensing over the 12–310 K range using three luminescence intensity ratio (LIR) readouts based on Yb³⁺ and Er³⁺ emissions, while complexes 2 and 3 provide single-ion-based thermometric responses. Among these, the Yb³⁺ (²F_5/2 → ²F_7/2)/Er³⁺(⁴I_13/2 → ⁴I_15/2) LIR yields the highest relative thermal sensitivity for 1, with a maximum value (S_m) of 2.5% K⁻¹ at 12 K, and 1.0% K⁻¹ at 310 K. Importantly, 1 represents the first heterodinuclear Yb–Er complex exhibiting thermometric properties and, more remarkably, enabling temperature sensing through three distinct LIR-based readouts. The Yb-only complex 2 exhibits S_m = 3.6% K⁻¹ at 110 K, among the highest reported for Yb³⁺ molecular thermometers, while Er-based readouts in 1 and 3 provide moderate sensitivities at higher temperatures. Comparative analysis highlights the role of Yb³⁺ → Er³⁺ energy transfer in modulating the thermometric behaviour of the heterodinuclear complex. Theoretical calculations support the presence of metal–metal and ligand-mediated energy-transfer pathways, which contribute to the observed temperature-dependent luminescence response.