Morphology-Dependent One- and Two-Photon Absorption Properties in Blue Emitting CsPbBr3 Nanocrystals

Abstract

The linear and nonlinear optical parameters and morphologic dependence of CsPbBr₃ nanocrystals (NCs) are crucial for device engineering. In particular, such information in asymmetric nanocrystals is still insufficient. We characterized the OPLA (σ¹) and TPA cross sections (σ²) of a series CsPbBr₃ nanocrystals with various aspect ratios (AR) using femtosecond transient absorption spectroscopy (TAS). The σ¹ presents a linear volume dependence of all the samples, which agrees with the previous behavior in CsPbBr₃ QDs. However, the σ² values do not exhibit conventional power dependency of the crystal volume but are also modulated by the shape-dependent local field factors. In addition, the local field effect in CsPbBr₃ NCs is contributed by their asymmetric morphologies and polar ionic lattices, which is more pronounced than in conventional semiconductor NCs. Finally, we revealed that the lifetimes of photogenerated multiexcitonic species of those nanocrystals feature identical morphology independence in both OPLA and TPA.

Figure 1

(A) Normalized UV–vis and PL of samples. (B) Histograms of nanoplatelet thicknesses. (C) Diagram of nanoplatelets. (D) TEM top and side view of NCs. (E) Picture of an excited sample with 385 nm light.

Figure 2

(A) OPLA cross section (σ¹) at 400 nm vs volume. (B) Volume-normalized OPLA cross-section (σ¹/V) vs thickness. (C) TPA cross section (σ²) at 800 nm vs volume. (D) TPA coefficient β vs thickness. Comparison of calculated results (This work) with reported results from (dSize-QDs)¹ and (dMorph)⁸.

Figure 3

Dependence of TPA coefficient β to AR of different-shaped NCs: blue squares are NPLs, and light blue triangles are NW. The green circles reported values of QDs, and the light green dots are calculated from local field theory at different AR for the different shapes. The AR is defined as AR_NW = L/d for NW, with L = length and d = diameter, AR_NPL = t/L for NPL with t = thickness and L = average length, and AR_QD = l_x/l_y for QD.

Figure 4

(A) Tail normalized GSB decay for NPL-1 excited at 400 nm. (B) Subtraction of one exciton decay from tail normalized GSB decay for NPL-1 excited at 400 nm. (C) Exciton lifetime at 400 nm excitation and 800 nm excitation in different thickness NCs. (D) Multiexciton lifetime at 400 nm excitation and 800 nm excitation in different thickness NCs.