A Selective Cation Exchange Strategy for the Synthesis of Colloidal Yb³⁺-Doped Chalcogenide Nanocrystals with Strong Broadband Visible Absorption and Long-Lived Near-Infrared Emission

Abstract

Doping lanthanide ions into colloidal semiconductor nanocrystals is a promising strategy for combining their sharp and efficient 4f-4f emission with the strong broadband absorption and low-phonon-energy crystalline environment of semiconductors to make new solution-processable spectral-conversion nanophosphors, but synthesis of this class of materials has proven extraordinarily challenging because of fundamental chemical incompatibilities between lanthanides and most intermediate-gap semiconductors. Here, we present a new strategy for accessing lanthanide-doped visible-light-absorbing semiconductor nanocrystals by demonstrating selective cation exchange to convert precursor Yb-doped NaInS nanocrystals into Yb-doped PbInS nanocrystals. Excitation spectra and time-resolved photoluminescence measurements confirm that Yb is both incorporated within the PbInS nanocrystals and sensitized by visible-light photoexcitation of these nanocrystals. This combination of strong broadband visible absorption, sharp near-infrared emission, and long (>400 μs) emission lifetimes in a colloidal nanocrystal system opens promising new opportunities for both fundamental-science and next-generation spectral-conversion applications such as luminescent solar concentrators.

Yb3+ and Yb3+/Er3+ doping for near-infrared emission and improved stability of CsPbCl3 nanocrystals

“…This value was similar to 815.0 μs of the Yb 3+ -doped PbIn 2 S 4 NCs and much longer than that of typical Yb 3+ organic ligands complexes (~10 μs). 44,45 Besides, Fig. 3b shows that the incorporation of Yb 3+ into CsPbCl 3 increases the average life time of the band edge emission of the CsPbCl 3 NCs from 3.9 to 8.2 ns.…”

“…Since the surface of the CsPbCl 3 NCs has many OA and OAm ligands, they readily diminish the NIR luminescence of Yb 3+ by the vibrations of the C–H, N–H, or O–H bonds. 44 They can also lead to shortened excited-state decay times and lower the PL QYs, if the Yb 3+ ions are closely adjacent to the ligands. 45 From the time-resolved PL decay tests, the luminescence decay–time of the 2 F 5/2 – 2 F 7/2 transition of the Yb 3+ ions inside the CsPbCl 3 NCs was found to be 941.9 μs (Fig.…”

Lanthanide doping in metal halide perovskite nanocrystals: spectral shifting, quantum cutting and optoelectronic applications

“…Therefore, for visible light optoelectronic applications, including solar light harvesting and LEDs, efforts have been made to dope Ln 3+ into the lattice of semiconductors. However, Ln 3+ doping in semiconductors has remained challenging because most semiconductors, such as CdSe, CdS, Si, GaAs, and InP, offer a tetrahedral (CN = 4) coordination environment for Ln 3+ dopants, whereas Ln 3+ ions prefer sites with CN ≥ 6 27,28 . It is noteworthy that lead halide perovskites are a rare class of semiconductors that possess octahedral coordination (CN = 6) for Pb (B-site cation); therefore, they provide an opportunity to dope lanthanide ions into optoelectronically active semiconductors.…”

Sensitized Yb3+ Luminescence in CsPbCl3 Film for Highly Efficient Near‐Infrared Light‐Emitting Diodes

“…However, light absorption ability of Yb 3+ itself is significantly smaller (ε = 1–100 dm 3 mol −1 cm −1 ) than that of organic dyes (ε = 10 4 –10 5 dm 3 mol −1 cm −1 ) because the electronic transitions of lanthanide ions are electric dipole forbidden (Laporte forbidden) transitions . To enhance NIR emission of Yb 3+ , sensitization, namely energy transfer from suitable donors with high absorption coefficient (as in this study) in colloidal nanocrystals (e.g., Cd or Pb chalcogenide) and in the form of Yb 3+ complexes with organic ligands, have been attempted so far . Unfortunately, their NIR PLQYs were still much small (<≈10%) compared to visible light emitting analogues, which prevents practical applications for NIR optoelectric devices.…”