Fig. 1. HR-TEM micrographs depicting the atomic resolution of both (a) flat-lying and stacked Mn-doped CsPbCl3 2D NPs and (b) cubic NCs. Subfigures (c), (d), and (e) show the distribution of the lengths, widths, and thicknesses of the 2D NPs, respectively, while (f) shows the edge size distribution of the cubic NCs.

Fig. 2. (a) UV-vis absorption and PL spectra of the 2D NPs and the cubic NCs. (b) Time-dependent PL intensity of Mn2+ at 592 nm measured from the 2D NPs and the cubic NCs. The insets show their colloidal solutions under UV illumination (λ=365  nm).

Fig. 3. (a) fs-TA data for the Mn-doped 2D NPs and cubic NCs pumped at 350 nm. (b) Recovery curves of the bleaching process at 383 nm for the 2D NPs and that at 387 nm for the cubic NCs. (c), (d) The excitation-intensity-dependent GSB signal amplitude at a time delay of 1 ns is shown for the 2D NPs and the cubic NCs. The curves are the best fit lines calculated based on Eq. (5).

Fig. 4. (a) PL spectra for the 2D NPs and cubic NCs excited by fs pulses at 680 nm. The inset shows the PL emissions of the 2D NPs and cubic NCs. (b) PL intensity versus excitation intensity with log–log plot slopes of 1.95 and 2.02, respectively. (c) 2PA and linear absorption spectra of the 2D NPs and cubic NCs plotted over the two- and one-photon energies. (d) Photo-induced energy transfer process from the host (CsPbCl3) to Mn2+ in the Mn-doped 2D NPs and cubic NCs under two-photon excitation.

Fig. 5. (a) PL spectra for the 2D NPs and cubic NCs excited by fs pulses at 1300 nm. The inset shows the PL emissions of the Mn-doped 2D NPs and cubic NCs. (b) PL intensity of the 2D NPs and cubic NCs versus the optical intensity with log–log plot slopes of 2.98 and 3.02, respectively. (c) 3PA spectra of the 2D NPs and cubic NCs. The inset shows solutions of the 2D NPs and cubic NCs in a pure host (CsPbCl3) under the same excitation intensity used for the inset of (a). (d) One-photon excitation spectra of the 2D NPs and cubic NCs detected at 592 nm. The inset shows the direct 3PA process from the A16 state to the T14 state in the Mn2+ of the 2D NPs and cubic NCs.

Fig. 6. Comparison of the maximum VN 2PA and 3PA cross sections of Mn-doped CsPbCl3 2D NPs and cubic NCs, as well as Mn-doped ZnS spherical NCs.