Lessons learned in autoclave synthesis of upconversion nanoparticles: unreported variables and safety considerations

Autoclaves – vessels for sustaining high temperatures and high pressures – are widely used across chemical and biological sciences, and are one of the more accessible pieces of equipment for synthesis of luminescent upconversion nanoparticles (UCNPs) amongst other nanomaterials. Yet, despite being crucial to nanomaterial synthesis, the details of autoclave reactors used are barely reported in the literature, leaving several key synthesis variables widely unreported, and thereby hampering the reproducibility of many synthesises. In this perspective, we discuss the safety considerations of autoclave reactors and note that autoclaves should only be used if they are (a) purchased from reputable suppliers/manufacturers and (b) have been certified compliant with relevant safety standards. Ultimately, using unsuitable autoclave equipment can pose a severe physical hazard and may breach legal workplace safety requirements. In addition, we highlight a number of parameters in autoclave synthesis that we suggest should be reported as standard in order to maximise the reproducibility of autoclave synthesis experiments. Subsequently, we discuss two case studies where a commercially available high-safety autoclave system was used to synthesise UCNPs. We also provide broader context for the physical and optical properties of UCNPs, their applications, and other UCNP synthesis methods. We hope that this perspective encourages users of autoclave synthesis, whether in nanomaterials or in broader contexts to: (a) adopt and report the use of high-safety autoclaves and (b) report the many experimental variables involved in autoclave use to enhance reproducibility and robustness of nanomaterial synthesis.