Two-photon absorption of FAPbBr_(3) perovskite nanocrystals

Perovskite nanocrystals(NCs) with high two-photon absorption(TPA) cross-section are of great interest due to their potential applications in three-dimensional optical data storage and multiphoton fluorescence microscopy. Among various perovskite materials, FAPbBr_(3) NCs show a better development prospect due to their excellent stability. However, there are few reports on their nonlinear optical properties. In this work, the nonlinear optical behavior of FAPbBr_(3) NCs is studied.The methods of multiphoton absorption photoluminescence saturation and open aperture Z-scan technique were applied to determine the TPA cross-section of FAPbBr_(3)NCs, which was around 2.76 × 10^(-45)cm^(4)·s·photon^(-1) at 800 nm. In addition,temperature-dependent photoluminescence induced by TPA was investigated, and the small longitudinal optical phonon energy and electron–phonon coupling strength was obtained, which confirm the weak Pb–Br interaction. Meanwhile, it is found that the exciton binding energy in FAPbBr_(3) NCs was 69.668 me V, which may be ascribed to the strong hydrogen bond interaction. It is expected that our findings will promote the application of FAPbBr_(3) NCs in optoelectronic devices.

Linear and nonlinear photophysical properties of ZnSe/CdS/ZnS core/shell/shell typeⅡnanocrystals

In this work,one kind of typeⅡZnSe/CdS/ZnS core/shell/shell nanocrystals(NCs)is synthesized,and their linear and nonlinear photophysical properties are investigated.Through measurements of the temperaturedependent photoluminescence spectra of NCs,their excitonic properties,including the coefficient of the bandgap change,coupling strength of the exciton acoustic phonons,exciton longitudinal optical(LO)phonons,and LO–phonon energy are revealed.Femtosecond transient absorption spectroscopy was employed to obtain insight into ultrafast processes occurring at the interface of ZnSe and CdS,such as those involving the injection of photoinduced electrons into the CdS shell,interfacial state bleaching,and charge separation time.At the end,their multiphoton absorption spectra were determined by using the z-scan technique,which yielded a maximum twophoton absorption cross section of 3717 GM at 820 nm and three-photon absorption cross section up to 3.9×10^-77cm^6·s^2·photon^-2at 1220 nm,respectively.The photophysical properties presented here may be important for exploiting their relevant applications in optoelectronic devices and deep-tissue bioimaging.

Influence of mixed organic cations on the nonlinear optical properties of lead tri-iodide perovskites

Metal halide perovskite materials have been widely studied recently due to their excellent optoelectronic properties.Among these materials,organic-inorganic hybrid perovskites have attracted much attention because of their relatively soft framework,which makes them more suitable for nonlinear optical(NLO)applications.However,there is rare physical mechanism study on the coexistence of two-photon absorption(TPA)and saturable absorption(SA)in organic-inorganic hybrid perovskite materials.To clarify this issue,the NLO properties of mixed cation perovskite MA1-xFAxPbI3[MA=CH3NH3,FA=CH(NH2)2,x=0,0.2,0.4,0.6,and 0.8]thin films are investigated in this paper.Based on the nonlinear transmittance and femtosecond-transient absorption spectrum measurements,it is found that the MA1-xFAxPbI3 materials exhibit NLO behavior dependent on excitation intensity.The TPA coefficient of MA1-xFAxPbI3 decreases with the increase of formamidinium(FA)content,while the relevant saturable intensity increases.In addition,it is revealed that the linear absorption process from valence band 2 to valance band 1 still exists even under a very low excitation intensity.With the increase of excitation intensity,the light transmittance at 1300 nm decreases first and then increases sharply,which also supports the explanation for the coexistence of TPA and SA.It is expected that our findings will promote the application of perovskite materials in nonlinear optoelectronic devices.

Superior multiphoton absorption properties in colloidal Mn-doped CsPbCl3two-dimensional nanoplatelets

We have studied the two-and three-photon absorption(2PA and 3PA) properties of Mn-doped CsPbCl_3 twodimensional nanoplatelets(2D NPs) and cubic nanocrystals. Compared with their cubic counterparts, the Mn-doped 2D NPs exhibit stronger quantum confinement effects that can more efficiently enhance their dopantcarrier exchange interactions and multiphoton absorption. More specifically, the maximum volume-normalized 2PA and 3PA cross sections of the 2D NPs were 6.8 and 7.2 times greater than those of their cubic counterparts,respectively, reaching up to 1237 GM∕nm^3 in the visible light band and 2.24 × 10^(-78) cm^6· s^2· photon^(-2)∕nm^3 in the second biological window, respectively.