Enhanced upconversion efficiency in LiYF4:Yb3+,Tm3+ nanocrystals by using anhydrous molecular precursors

A major challenge in the field of up-conversion nanomaterials (UC) is the search for improved up-conversion luminescence. Compared to conventional luminophores, the quantum yields of lanthanide-doped nanoparticles are extremely low (typically <1%) and, in general, about an order of magnitude lower than those of corresponding up-conversion bulk materials [1]. It is well known that OH defects in nanocrystals are the main cause of up-conversion quenching [2]. Although SiO2@UCNP core-shell architectures are an established approach of increasing the efficiency of upconversion luminescence, this strategy cannot be universally used for all types of applications. We used anhydrous molecular precursors as a synthesis strategy to improve the up-conversion efficiency in lanthanide-doped nanocrystals (NCs). These well-defined molecular precursors allow to obtain different morphologies of LiYF4:Yb+3,Tm+3 nanocrystals under different conditions, which exhibit up-conversion efficiency comparable to that of UC bulk material. This work will describe the synthesis and full characterization of new lanthanide precursors and LiYF4:Yb+3,Tm+3 NCs as well as a comparative up-conversion study of nanocrystals and single crystals. References: [1] G. Tessitore, G. A. Mandl, M. G. Brik, W. Park, J. A. Capobianco, Recent insights into upconverting nanoparticles: spectroscopy, modeling, and routes to improved luminescence, Nanoscale (2019) 11, 12015–12029. [2] Z. Wang, A. Meijerink, Concentration Quenching in Upconversion Nanocrystals, J. Phys. Chem. C (2018) 122, 26298−26306.