The aim of this work was i) to develop ah ydrothermal, low-temperature synthesis protocola ffording the upconverting hexagonal phaseN aYF 4 with suitable dopants while adhering to the "green chemistry" standards and ii)to exploret he effect that different parameters have on the products. In optimizingt he synthesis protocol, short reaction times andl ow temperatures (below 150 8C) were considered. Yb 3 + and Er 3 + ions were chosen as dopants for the NaYF 4 material. Within the context of the second goal, parameters including nature of the precursors, treatment temperature, and treatment time were investigatedt oa fford ap ure hexagonal crystalline phase, both in the dopeda nd undoped materials. To fully explore the synthesis results, the prepared materials were characterized from as tructural (XRD),c ompositional (XPS, ICP-MS), and morphological (SEM) point of view.T he upconverting properties of the compounds were confirmed by photoluminescence measurements.[a] N.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.