Heteroepitaxial Growth to Construct Hexagonal/Hexagonal β‐NaYF₄:Yb,Tm/Cs₄PbBr₆ Multi‐Code Emitting Core/Shell Nanocrystals

Abstract

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‐NaYF4 and hexagonal Cs4PbBr6 are filtrated to construct the UCNP/MHP heterostructural luminescent material. The similarity in their crystal structures facilitate the heteroepitaxial growth of Cs4PbBr6 on the surface of β‐NaYF4 NPs, leading to the formation of high‐quality β‐NaYF4:Yb,Tm/Cs4PbBr6 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 Tm3+ to Cs4PbBr6. It is noteworthy that the FRET efficiency of β‐NaYF4:Yb,Tm/Cs4PbBr6 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 Cs4PbBr6. 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.

Surface and Interface Engineering for Highly Stable CsPbBr3/ZnS Core/Shell Nanocrystals

“…Lead halide perovskite (LHP) nanocrystals (NCs) have received tremendous attention due to their superior optoelectronic properties, such as near-unity photoluminescence quantum yield (PLQY), with a narrow full width at half-maximum (fwhm) and high absorption coefficient. − These unique properties make LHP NCs promising photosensitive materials for their wide applications in optoelectronic devices, such as solar cells, light-emitting diodes (LEDs), and photodetectors. − Unfortunately, the poor stability, especially low moisture/aqueous stability, of LHP NCs is becoming one of the most crucial drawbacks that significantly compromises the performance of LHP NC-based optoelectronic devices. − Moreover, the poor stability under high-moisture/aqueous conditions also hinders their further applications. , …”

Dual-Mode Luminescence from Polyacrylonitrile-Stabilized CsPbX3 (X = Br and I) Nanocrystals Triggered by NaYF4:Yb/Ln (Ln = Er and Tm) Upconversion Nanoparticles: Implications for Anticounterfeiting and Optical Thermometry

“…In recent years, all-inorganic cesium lead halide perovskite quantum dots (PeQDs) have received extensive research attention due to their excellent optical properties, such as high photoluminescence quantum yield (PLQY), high absorption coefficient, narrow emissive bands, long carrier diffusion length, and tunable bandgap and emission peaks by adjusting halogen components. − These unique emissive characteristics enable PeQDs to have promising applications in optoelectronic and photovoltaic fields. Compared with UV/vis-excitable linear emission (downshifting or photoluminescence), nonlinear upconversion (UC) luminescence of PeQDs upon NIR excitation holds great promise in deep-tissue bioimaging, advanced fluorescent anticounterfeiting, and solar spectrum conversion due to the advantages of large penetration depth, minimal background interference, and color-tunable luminescence. − However, NIR-excited UC luminescence of PeQDs is limited by the lack of intermediate energy levels, the low multiphoton absorption efficiency (<10 –8 ), and the requirement of expensive high-energy pulsed lasers. In comparison, lanthanide-doped upconversion nanomaterials (UCNPs) can be efficiently excited by a low-cost diode laser, generating highly efficient UC luminescence (>10 –3 ) via multistep photon absorption and successive energy transfer processes. , Unfortunately, owing to the defined and discrete energy states of lanthanide ions, these UCNPs possess upconverting emissions at fixed wavelengths.…”