Large third-order optical nonlinearities of two-dimensional CsPbBr3 nanoplatelets

Abstract

Metal halide perovskites show considerable optical nonlinearity and could be used for cost-effective nonlinear optical devices if their nonlinear susceptibilities can be improved. Here, we report large optical nonlinearity, including third-order nonlinear absorption, refraction, and two-photon absorption excited luminescence, of CsPbBr3 nanoplatelets with a thickness of two or three atomic layers and a plane size of about 60 nm. Specifically, the nonlinear absorption was mainly induced by two-photon absorption at low incident powers, and the nonlinear absorption cross section reached 2.15 × 107 GM. It is two orders of magnitude larger than that of CsPbBr3 nanocrystals, which makes them an ideal optical limiting material. Furthermore, the nanoplatelets exhibited large self-phase modulation-induced nonlinear refraction, and the figures of merit W and T satisfied W >1 and T <1, which allow for optical switching. The large optical nonlinearity of CsPbBr3 nanoplatelets provides a basis for multifunctional applications in nonlinear optical devices.

Dimension and Thickness Control Synthesis of Strongly Confined Cesium Lead Iodide Perovskites with Excellent Two-Photon Absorption Properties

“…To validate our finding, we have also measured σ 2 for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs using the Z-scan technique. − For this purpose, we have used a Ti-sapphire laser with 100 fs pulse width and 80 MHz repetition rate, as we have reported before. − The normalized transmittance for Z-scan measurement for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs can be expressed as follows − T 0.25em ( 2 PA ) = 1 true{ 1 + α 2 L eff [ I 0 1 + ( Z / Z normalr false) 2 ] true} L eff = [ 1 − normale − α oL α 0 ] where L eff is the effective thickness of the sample for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs, α 2 is the two-photon optical coefficient for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs, Z is the position for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs in the light path during the measurement, α o is the linear absorption for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs and 3D CsPbI 3 NCs, I 0 is the laser peak intensity at the focal point where Z = 0, and Z r is the Rayleigh length. − …”

“…To validate our finding, we have also measured σ 2 for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs using the Z-scan technique. − For this purpose, we have used a Ti-sapphire laser with 100 fs pulse width and 80 MHz repetition rate, as we have reported before. − The normalized transmittance for Z-scan measurement for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs can be expressed as follows − where L eff is the effective thickness of the sample for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs, α 2 is the two-photon optical coefficient for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs, Z is the position for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs in the light path during the measurement, α o is the linear absorption for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs and 3D CsPbI 3 NCs, I 0 is the laser peak intensity at the focal point where Z = 0, and Z r is the Rayleigh length. − Using experimental data as reported in Figure H,I and eqs and 7, we have determined σ 2 for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs, which are reported in Table . From the reported data, we find that the σ 2 for 3D CsPbI 3 NCs is 1.6 × 10 6 GM, which matches very well with the two-photon luminescence measurement.…”

“…As we and others have reported before, photoinduced transition dipole moment is one of the important factors for the two-photon process. − It is now well documented that the photoinduced transition dipole moment for NPLs is dependent on the exciton oscillator strength. − The overlap of electron and hole wave functions, which is known as the electron–hole pair, is the dominating factor for the photoinduced transition dipole moment. − As it is now well documented, in the weak confinement regime, the overlap between the electron and hole wave functions of the two excitons is low, and as a result, the movement of electrons and holes is free. Due to the above fact, the photoinduced dipole moment is small. − On the other hand, in the strong confinement regime, the overlap between the electron and hole wave functions of the two excitons is high, which enhances the two-pair exciton oscillator strength. − As a result, the photoinduced dipole moment is enhanced and exhibits higher TPA properties. As reported in Figure L, experimentally observed σ 2 values for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs do not follow the same trend with QCP as we have observed for 2D CsPbI 3 NPLs with different thicknesses.…”

“…Next, to find out how the two-photon absorption cross section (σ 2 ) varies with the dimension and thickness of cesium lead halide perovskites, we have determined the σ 2 values for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs using a two-photon luminescence (TPL) experiment. − For this purpose, we have used a Ti-sapphire laser with 880 nm as an excitation source, as we have reported before. − The absolute σ 2 values for 0D-NCs, 1D-NWs, 2D-NPLs, and 3D-NCs were calculated using fluorescein as the reference whose TPA cross sections are known in the literature, as we and others have reported before. − TPA cross sections for 0D-NCs, 1D-NWs, 2D-NPLs and 3D-NCs were determined using eq − σ 2 , 0 normalD = ( F 0 normalD F fluorescein ) ( Φ fluorescein Φ 0 normalD ) ( C fluorescein C 0 normalD ) where σ 2,0D is the two-photon absorption cross section for 0D Cs 4 PbI 6 NCs, F 0D is the observed two-photon fluorescence intensity of 0D Cs 4 PbI 6 NCs, F fluorescein is the observed two-photon fluorescence intensity of fluorescein, Φ 0D is the quantum yield for 0D ...…”

“…Due to the three-direction space coupling nature, 3D CsPbX 3 are known to exhibit low exciton binding energies, and excitons can dissociate easily to form free charge carriers. − Since low-dimensional CsPbX 3 semiconductor nanocrystals exhibit unique optical and optoelectronic properties, several research groups are working to develop three-dimensional (3D) to zero-dimensional (0D) perovskites with tunable band gaps, which have the capability to be used in different photoelectronic devices such as light-emitting diodes (LEDs), lasers, and photodetectors. − …”