Upconverting mixed emitter nanocomposites as sensitive luminescent thermometers within plant-inspired artificial fliers*

Abstract

The applicability of current upconverting lanthanide doped luminescent thermometers is limited by signal discriminability and thermal sensitivity. We overcome these limitations by creating fluorescent nanocomposites in biodegradable polyhydroxyalkanoates (PHA). Nanocomposites were designed that combine different lanthanide based upconverting nanoparticles. We create mixed emitter composites with bright red (Mn 2+ doped with Er 3+ , Yb 3+ in NaYF4), green (Er 3+ , Yb 3+ in BaYF5) and blue (Tm 3+ , Yb 3+ in CaF2) emitting particles to obtain clearly distinguishable and intense fluorescent signals. The resulting nanocomposites had maximum relative thermal sensitivities of 34% K -1 , outperforming existing thermometers.Importantly, their readout requires detection only in visible wavelength ranges, making them particularly suitable for dronebased environmental monitoring purposes. To demonstrate their applicability in this field, we integrate the nanocomposites into plant-inspired artificial fliers, creating self-deployable and biocompatible units for wireless monitoring of environmental temperature. The surface temperature of topsoil is reconstructed based on the fluorescence intensity ratio among the RGB (red-green-blue) wavelengths of the upconverting nanocomposites integrated into the fliers.