Tunable, Exciton-Driven Multiphoton Absorption in CsPbX3 (X = Cl, Br, I) Perovskite Nanocrystals under Femtosecond Excitation

Abstract

The excellent photophysical and nonlinear optical (NLO) properties of lead halide perovskite (LHP) nanocrystals (NCs) offer a gamut of applications in optoelectronics and photonics. In this work, we have investigated the intensity-dependent NLO responses of CsPbX3 (X = Cl, Br, and I) NCs deploying the femtosecond (fs) Z-scan experimental method. An 800 nm central wavelength laser with a ∼50 fs pulse width and 1 kHz repetition rate was used as the pump source. Our studies revealed the possibility of tuning the multiphoton absorption (MPA) order and the MPA coefficient by changing the halide site in the perovskite NCs. At 800 nm fs excitation, these LHPs exhibited reverse saturable absorption in the open-aperture Z-scan experiment, where CsPbCl3 NCs have demonstrated four-photon absorption, while CsPbBr3 and CsPbI3 NCs have depicted three-photon absorption. The MPA coefficients were found to be (3.92, 2.53, and 1.82) × 10–34 cm5/W3 for CsPbCl3 at different peak intensities. On the other hand, the same was determined to be (6.80, 4.60, and 3.20) × 10–23 and (2.86, 2.42, and 2.67) × 10–23 cm3/W2 for CsPbBr3 and CsPbI3 NCs, respectively. The closed-aperture Z-scan measurements, on the contrary, revealed a self-focusing behavior of these LHP NCs through the valley–peak transmittance signature. Correspondingly, we have determined other NLO parameters such as MPA cross sections (σ4, σ3), nonlinear refractive index (n2), and real part of third-order susceptibility (Re|χ(3)|), all pointing to their exceptional potential to be a worth while contender in contemporary optoelectronic and nonlinear optical applications.