The remarkable optical properties of the lanthanides (Ln) make Ln-based materials ideal for applications ranging from biomedicine to optoelectronics and energy conversion technology. This is due the unique electronic properties of the Ln (f-elements) allowing for upconversion, i.e., the emission of UV-visible light under near-infrared excitation. Upconverting nanoparticles (UCNPs) based on sodium lanthanide fluorides (NaLnF4) are commonly synthesized by the thermal decomposition of metal precursors in high-boiling-point solvents, based on convectional heating. Microwave reactors can improve reproducibility as offering better control over a reaction environment, more homogeneous heat distribution yields narrow size distributions, and rapid heating to the desired temperature shortens reaction times from hours to minutes. Targeting applications in optoelectronics, photochemistry, and energy conversion, boosting the efficiency of upconverters is key. This presentation will shed light on the microwave-assisted synthesis of core/(multi)shell UCNPs and highlight pros and cons of this strategy towards the design of small-yet-bright upconverters.