Controlling the Energy‐Transfer Processes in a Nanosized Molecular Upconverter to Tap into Luminescence Thermometry Application

Photon upconversion (UC) in molecular species remains a highly sought-after property with vast potential applications in many fields. Until now, a few reports on molecular upconverters are limited to demonstrating upconversion. The low UC quantum yields (QY) and nuclearities hindered the application capabilities for molecular upconverters. To overcome these limitations, we report the use of a molecular cluster-aggregate (MCA) containing 20 lanthanide ions to target YbIII -TbIII -based cooperative UC. Upconversion quantum yield value of 1.04×10-4 %, among the highest value observed for a molecular cooperative UC, was attained for the {Gd11 Tb2 Yb7 } composition. Substitution of GdIII ions for EuIII centers opens a YbIII →TbIII →EuIII energy-transfer pathway, allowing the first proof-of-concept of potential application for molecular UC. This report on upconversion-based luminescence thermometry in a molecular species endorses further development of upconversion properties of nanoscale MCAs.