Heteroepitaxial Growth to Construct Hexagonal/Hexagonal β-NaYF 4 :Yb,Tm/Cs 4 PbBr 6 Multi-Code Emitting Core/Shell Nanocrystals.

Synthesis of upconversion nanoparticles (UCNPs)-metal halide perovskites (MHPs) heterostructure is garnered immense attentions due to their unparalleled photophysical properties. However, the obvious difference in their structural forms makes it a huge challenge. Herein, hexagonal β-NaYF 4 and hexagonal Cs 4 PbBr 6 are filtrated to construct the UCNP/MHP heterostructural luminescent material. The similarity in their crystal structures facilitate the heteroepitaxial growth of Cs 4 PbBr 6 on the surface of β-NaYF 4 NPs, leading to the formation of high-quality β-NaYF 4 :Yb,Tm/Cs 4 PbBr 6 core/shell nanocrystals (NCs). Interestingly, this heterostructure endows the core/shell NCs with typically narrow-band green emission centered at 524 nm under 980 nm excitation, which should be attributed to the Förster resonance energy transfer (FRET) from Tm 3+ to Cs 4 PbBr 6 . It is noteworthy that the FRET efficiency of β-NaYF 4 :Yb,Tm/Cs 4 PbBr 6 core/shell NCs (58.33%) is much higher than that of the physically mixed sample (1.84%). In addition, the reduced defect density, lattice anchoring effect, as well as diluted ionic bonding proportion induced by the core/shell structure further increase the excellent water-resistance and thermal cycling stability of Cs 4 PbBr 6 . These findings open up a new way to construct UCNP/MHP heterostructure with better multi-code luminescence performance and stability and promote its wide optoelectronic applications.