A modular platform for in-flow synthesis and characterization of upconverting nanoparticles.

High-temperature colloidal synthesis of upconverting nanoparticles (UCNPs) is highly sensitive to reaction temperature and time, solvent composition, and thermal history, thus making reproducible synthesis and UCNP property mapping challenging. Here, we introduce an automated fluidic platform for high-temperature stop-flow synthesis and in-line optical characterization of NaYF4-based UCNPs. The platform includes modules for reagent supply and mixing, high-temperature synthesis, and in-line optical characterization. The platform was used for the evaluation of the effects of reaction temperature, time, and solvent composition on two key UCNP optical performance metrics: the red-to-green photoluminescence emission intensity ratio and relative quantum yield. Reproducibility tests confirmed robust reactor operation and reliable optical measurements. The UCNPs synthesized in the fluidic platform and using conventional batch synthesis exhibited similar properties, but the fluidic synthesis occurred significantly faster. The developed fluidic platform offers a modular approach to the automated UCNP synthesis and establishes a foundation for future closed-loop, machine-learning-guided optimization of high-temperature nanomaterial synthesis.