Near-infrared-pumped photon upconversion in CsPbI3 and CaF2:Yb3+/Ho3+ nanocomposites for bio-imaging application

All-inorganic CsPbX 3 (X = Cl, Br, and I) perovskite quantum dots (PeQDs) have gained intensive attentions due to their excellent linear properties and promising applications in optoelectronics and photovoltaics. However, due to the limitation of nonlinear upconversion, the multiphoton absorption efficiency in PeQDs is very low. Here, we present the near-infrared-pumped upconversion (UC) luminescence of CsPbI 3 PeQDs sensitized by CaF 2 :Yb 3+ /Ho 3+ hierarchical nanospheres (HNSs) in the CsPbI 3 and CaF 2 :Yb 3+ /Ho 3+ nanocomposite structure. By introducing appropriate proportion of Br − ions, UC luminescence can be easily tuned from 695 nm to 655 nm. The lifetimes of CsPbI 3 PeQDs excitonic emissions are lengthened to several milliseconds during the energy transfer process from the long-lived Ho 3+ to CsPbI 3 PeQDs, which can be tuned by changing the Br/I ratio. The stability of CsPbI 3 PeQDs is enhanced in the composites, which keeps 90 % photo luminescence after 30 days. The composites are printed on the flexible substrate for dual-mode fluorescent encryption anti-counterfeiting application, which display excellent fluorescence under the excitation of both ultraviolet and near-infrared light. Moreover, the CsPbI 3 and CaF 2 :Yb 3+ /Ho 3+ nanocomposites are highly water-soluble, which demonstrate ultrastability and high biocompatibility in the cell imaging application. This work provides a new strategy to develop photon upconversion in PeQDs, and blazes a new trail for the development of multifunctional materials. • The composite structure is synthesized, which achieves near-infrared-pumped upconversion luminescence. • This composite structure has extraordinary humidity and oxygen stability. • Efficient dual-mode bio-imaging is achieved by using this composite structure with the capability of up-conversion and down-conversion concurrently.