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+ (2F5/2 → 2F7/2)/Er3+(4I13/2 → 4I15/2) LIR yields the highest relative thermal sensitivity for 1, with a maximum value (Sm) 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 Sm = 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.