High-Quantum-Yield Upconverting Er<sup>3+</sup>/Yb<sup>3+</sup>-Organic–Inorganic Hybrid Dual Coatings for Real-Time Temperature Sensing and Photothermal Conversion
Fábio José Caixeta, Ana R. N. Bastos, Alexandre M. P. Botas, Leonardo Sousa Rosa, Vítor dos Santos de Souza, Fernanda Hediger Borges, Albano N. Carneiro Neto, Alban Ferrier, Philippe Goldner, Luís D. Carlos, Rogéria Rocha Gonçalves, Rute A. S. Ferreira
Abstract
Flexible coatings with dual capabilities for remote real-time temperature sensing and photothermal conversion have a huge potential in the field of advanced thermal actuated optoelectronic applications. In this work, we demonstrated that plastic free-standing films of Er3+/Yb3+-codoped GeO2–Ta2O5 particles dispersed in poly(methyl methacrylate) (PMMA) having intriguing upconversion high absolute emission quantum yield (∼0.1452, excited at 980 nm, 760 W·cm–2) can simultaneously operate as photothermal converters and real-time primary thermometers. The emission of the films was studied at the microscale, revealing emission homogeneity detected through surface hyperspectral microscopy. One factor that contributes to the unusually high absolute emission quantum yield, when compared with other oxides-based materials, is the high occurrence (probability) of the shortest Yb–Er distances obtained when the YbTaO4 phase is formed. This, as demonstrated by computational simulations of doping processes, favors the Yb-to-Er energy transfer rates, enhancing the population of the Er3+ emitting levels. Besides, the films combined a relative thermal sensitivity of ∼1.1% K–1 (at 300 K) with a temperature uncertainty of ∼0.7 K and a maximum photothermal efficiency of ∼44%, which permits the prospect of using this material as a coating with photothermal and thermometer functions. Moreover, as an added benefit, the thermal resistance of the composite in PMMA was estimated, yielding a maximum value of 760 ± 8 K·W–1. This is the first example of an active coating for photothermal conversion with the simultaneous ability to remotely sense temperature that can be explored in NIR-pumped free-space telecommunications without the need of additional optoelectronics devices.