Comparison Studies of the Linear and Nonlinear Optical Properties of CsPbBrxI3-x Nanocrystals: The Influence of Dimensionality and Composition

The optoelectronic properties of all-inorganic perovskite nano crystals (NCs) have been widely investigated, but the relevant studies have mainly focused on CsPbBr3 NCs. The photophysical properties of other all-inorganic perovskite NCs, such as CsPbBrxI3-x (0 <= x < 3), have not been fully explored. Herein, we report comprehensive comparison studies on the linear and nonlinear optical (NLO) properties of colloidal CsPbBrxI3-x NCs, that is, CsPbBr2.7I0.3 two-dimensional nanoplatelets (2D NPs) and cubic NCs of CsPbBr2.7I0.3 and CsPbI3. Temperature-dependent photoluminescence (PL) measurements confirm that the 2D NPs exhibit higher PL color purity at elevated temperatures than their cubic counterparts. By using femtosecond-transient absorption spectroscopy, the linear absorption cross sections are determined. Importantly, it is found that the 2D NPs show more efficient volume-normalized two-photon absorption than their cubic counterparts due to the contribution of strong electronic confinement. Studies on the relevant influences of dimensionality and composition on the linear and NLO properties of perovskite NCs are not only interesting for relevant applications but also important for fundamental physics.