Lanthanide Tris-Acetylacetonate Complexes for Luminescent Thermometry: From Isolated Compounds to Hybrid Prussian Blue Core–Silica Shell Nanoparticles

Precise remote temperature sensing at the micro- and nanoscale is a growing necessity in modern science and technology. We report a series of luminescent tris-acetylacetonate lanthanide complexes, Ln(acac)3(H2O)2 (Ln = Eu (1Eu), Tb (1Tb), Yb (1Yb)); acac− = acetylacetonate), operating as self-referenced thermometers in the 290–350 K range, both in the solid state and when embedded in hybrid nanoparticles. Among the investigated systems, the Eu3+ complex exhibits excellent lifetime-based thermometric performance, achieving a maximum relative sensitivity (Srmax) of 2.9%·K−1 at 340 K with a temperature uncertainty (δT) as low as 0.02 K and an average temperature uncertainty (δT¯) of 0.5 K, placing it among the most effective ratiometric lanthanide-based luminescent thermometers reported to date. The Yb3+ analog enables intensity-based thermometry in the near-infrared domain with a good sensitivity Srmax = 0.5%·K−1 at 293 K, δT = 0.5 K at 303 K, and δT¯ = 1.6 K. These molecular thermometers were further incorporated into the shell of Prussian Blue@SiO2 core–shell nanoparticles. Among the resulting hybrids, PB@SiO2-acac/(1Tb/1Eu) (with a Tb/Eu ratio of 2/8) stood out by enabling ratiometric temperature sensing based on the Eu3+5D0 → 7F2 lifetime, with satisfactory parameters (Srmax = 0.9%·K−1, δT = 0.21 K at 303 K, and δT¯ = 1.1 K). These results highlight the potential of simple coordination complexes and their nanohybrids for advanced luminescent thermometry applications.