Advancing the upconversion materials field relies on accurate and contrastable photoluminescence efficiency measurements, which are characterised by the absolute upconversion quantum yield (UCQY). However, the methodology for such measurements cannot be extrapolated directly from traditional photoluminescence quantum yield techniques, primarily due to issues that arise from the non-linear behaviour of the UC process. Subsequently, no UCQY standards exist, and significant variations in their reported magnitude can occur between laboratories. In this work, our aim is to provide a path for determining and reporting the most reliable UCQYs possible, by addressing all the effects and uncertainties that influence its value. Here the UCQY standard, at a given excitation power density, is defined under a range of stated experimental conditions, environmental conditions, material properties, and influential effects that have been estimated or corrected for. A broad range of UCQYs reported for various UC materials are scrutinized and categorized based on our assertion of the provided information associated with each value. This is crucial for improved comparability with other types of photoluminescent materials, and in addition, the next generation of UC materials can be built on top of these reliable standards.
Keywords: 102 Porous/Nanoporous/Nanostructured materials; 107 Glass and ceramic materials; 204 Optics/optical applications; 206 Energy conversion/transport/storage/recovery; 40 Opticalmagnetic and electronic device materials; 505 Optical/molecular spectroscopy; NaYF4; PLQY; UCQY; Upconversion quantum yield; lanthanides; photoluminescence efficiency characterization; photoluminescence quantum yield; rare-earth dopants; upconversion nanoparticles; upconversion phosphors.
© 2021 The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis Group.