Giant five-photon absorption from multidimensional core-shell halide perovskite colloidal nanocrystals

Abstract

Multiphoton absorption processes enable many technologically important applications, such as in vivo imaging, photodynamic therapy and optical limiting, and so on. Specifically, higher-order nonlinear absorption such as five-photon absorption offers significant advantages of greater spatial confinement, increased penetration depth, reduced autofluorescence, enhanced sensitivity and improved resolution over lower orders in bioimaging. Organic chromophores and conventional semiconductor nanocrystals are leaders in two-/three-photon absorption applications, but face considerable challenges from their small five-photon action cross-sections. Herein, we reveal that the family of halide perovskite colloidal nanocrystals transcend these constraints with highly efficient five-photon-excited upconversion fluorescence—unprecedented for semiconductor nanocrystals. Amazingly, their multidimensional type I (both conduction and valence band edges of core lie within bandgap of shell) core–shell (three-dimensional methylammonium lead bromide/two-dimensional octylammonium lead bromide) perovskite nanocrystals exhibit five-photon action cross-sections that are at least 9 orders larger than state-of-the-art specially designed organic molecules. Importantly, this family of halide perovskite nanocrystals may enable fresh approaches for next-generation multiphoton imaging applications.

Confinement of Perovskite‐QDs within a Single MOF Crystal for Significantly Enhanced Multiphoton Excited Luminescence

“…The slope (that is, the order of MPE process) of 2.03 is very close to 2, indicating that the twophoton excitation (2PE) luminescence process occurs. [7] But first, we need to determine that the properties of the synthesized MAPbBr 3 -NCs are consistent with the reported properties. Such behavior is consistent with the nature of the multiphoton excitation process.…”

“…It has been known that the perovskite quantum dot (QD) MAPbBr 3 are very promising MPE luminescent materials, herein we develop a novel approach to confine high-quality perovskite QD MAPbBr 3 single crystals into a bulky MOF ZJU-28 (ZJU-28 = [In 3 (BTB) 4 ] (Me 2 NH 2 ) 3 ) [12] single crystal, and thus report the novel example of single crystal five-photon excited luminescence materials with high multiphoton action cross-sections that can rival the current highest record (measured in toluene solution), [7] and excellent photostability. It has been known that the perovskite quantum dot (QD) MAPbBr 3 are very promising MPE luminescent materials, herein we develop a novel approach to confine high-quality perovskite QD MAPbBr 3 single crystals into a bulky MOF ZJU-28 (ZJU-28 = [In 3 (BTB) 4 ] (Me 2 NH 2 ) 3 ) [12] single crystal, and thus report the novel example of single crystal five-photon excited luminescence materials with high multiphoton action cross-sections that can rival the current highest record (measured in toluene solution), [7] and excellent photostability.…”

“…[18,19] Under 27 °C and 60% humidity, we studied the photostability of ZJU-28⊃MAPbBr 3 single crystals and MAPbBr 3 -NCs (dispersed in toluene, for the comparison). [7,20] The emission intensity rapidly decreases as the toluene solvent evaporates and no luminescence was observed after 120 s when the solvents were completely evaporated. Figure S6 (Supporting Information) shows the time-dependent luminescence spectrum of the synthesized MAPbBr 3 -NCs dispersed in toluene tested in air (the NCs dispersed toluene solution was dropped on the quartz plate for testing, basic characterizations can be found in the Supporting Information and Figure S5).…”

“…For 960 nm excitation, as the pump energy density increases, the luminescence intensity of the material gradually increases without accompanying the obvious emission peak shift (single pulse energy threshold of E th ≈ 0.035 mJ cm −2 ), and there is a linear relationship between the logarithm of the emission intensity and the logarithm of the pump energy density (Figure 5a). [6,7,[23][24][25] We choose the MAPbBr 3 -NCs as the reference sample due to the synthesis conditions are relatively mature, and the MPACs www.advmat.de www.advancedsciencenews.com (up to five-photon) of MAPbBr 3 NCs have been investigated. When excited at 1440 (Figure 5b), 1800 (Figure 5c), and 2100 nm (Figure 5d), the required minimum pump energy densities to generate MPE luminescence in the single ZJU-28⊃MAPbBr 3 crystal are significantly increased, that is, E th ≈ 0.3 mJ cm −2 for 1440 nm, E th ≈ 5.0 mJ cm −2 for 1800 nm, and E th ≈ 15 mJ cm −2 for 2100 nm excitation, respectively.…”

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and then generate a high-energy photon through radiation transitions from the excited state. [6,7] The deficiency of bulky high-order MPE luminescence solid single crystals with low excitation threshold have further limited the exploration and implementation of such MPE materials into miniaturization and device, and thus their practical applications.Some porous materials such as mesoporous silica and porous alumina have been utilized to confine dye molecules and perovskite nanoparticles and thus to diminish the ACQ and to develop the solid-state luminescence. Even for those materials exhibiting such MPE luminescence, the five-photon excited luminescence phenomena can be only observed in the dispersed solutions of either organic chromophore molecules or core-shell halide perovskite semiconductor nanocrystals (MAPbBr 3 /(OA) 2 PbBr 4 ) in order to diminish the aggregation-caused quenching (ACQ) while still with quite low multiphoton action cross-sections (MPACs), or have poor stability without any encapsulation approaches (The MPAC (ησ n ) is the product of photoluminescence quantum yield (PLQY, η) and multiphoton absorption cross-section (σ n ), the parameter to evaluate the multiphoton excited luminescence brightness).

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