Double bond terminated Ln3+-doped LiYF4 nanocrystals with strong single band NIR emission: simple click chemistry route to make water dispersible nanocrystals with various functional groups

Abstract

We developed a versatile and simple strategy for converting hydrophobic upconverting nanocrystals into water dispersible nanocrystals with a variety of functional groups at the surface using thiol–ene click chemistry. This was achieved by covalently linking thiol groups containing molecules, such as cysteine, cysteamine, 3-mercaptopropanoic acid and 2,3-dimercapto-1-propanol, to undecenoic acid capped Yb³⁺/Tm³⁺ doped LiYF₄ nanocrystals via click chemistry in the presence of azobisisobutyronitrile (AIBN). This method allows the provision to place variety of functional groups on the surface of the nanocrystals. The shape and size of the nanocrystals were preserved, even after surface modification. Interestingly, the undecenoic acid capped Yb³⁺/Tm³⁺ doped LiYF₄ nanocrystals showed strong emission in the NIR region compared to emissions in the visible region.