Light-Activated Upconverting Spinners

Rare earth doped upconverting particles (UCPs, capable of efficient infrared-to-visible light conversion) have played a fundamental role in the development of up-to-date photonics. Thanks to their unique combination of properties (high brightness, superior spectral and intensity stabilities, and high biocompatibility) old dreams have become possible such as obtaining intracellular dynamical images or remote measurement of temperature in the nanoscale. In this work, it is demonstrated how a rarely considered property of UCNPs, their intrinsic optical birefringence, expands their multifunctionality by converting them into fully controlled, optically activated luminescent spinners. Thanks to the luminescence-based thermal sensing ability of upconverting spinners, it is possible, by comparison between experimental data and numerical modeling, to explain the supralinear behavior of spinning rate with optical power. The complete understanding of rotation dynamics allows the use of UCPs as mechanical microthermometers with thermal sensitivities larger than those traditionally achieved by luminescence-based thermometry. Experimental demonstration of the potential use of UCPs as remote light-activated microrotors is also provided. Results included in this work constitute the first step toward the overcoming of new challenges in photonics including those raising in modern biophotonics and colloidal science.