Figure shows the absorption and emission spectra of all the samples with the respective picture of a quartz cuvette containing their hexane suspensions under UV light. The intense excitonic absorption implies in strong quantum confinement effect along of the thickness of the PNPls. The position of the excitonic absorption is directly related to the number of octahedron layers (n) in each PNPl: in the case of the CsPbBr3 compositions, we have well defined n = 2 (λexc = 425 nm, Br-110) and n = 3 (λexc = 454 nm, Br-170) excitonic maxima in the absorption spectra. For CsPbI3 compositions, sample I-110 shows predominantly n = 3 excitonic absorption (λexc = 587 nm), while I-170 shows a mixture of thicker particles together with the n = 3 excitonic peak. Regarding the PL spectra, samples synthesized at 110 °C show more intense emissions from the main excitonic state: n = 2 for Br-110 (λmax = 439 nm) and n = 3 for I-110 (λmax = 606 nm). The latter also shows a shoulder that is possibly the emission of the PNPls with n = 4. Sample Br-170 also shows intense n = 3 emission (λmax = 465 nm) along with emissions from thicker PNPls. In the case of samples Br-170 and I-110, the intense PL from thicker PNPls (n > 3) is most likely due to reabsorption effects, given the geometry (90 °) and concentration (0.2 mg/mL) measurements were performed (see Methods). Finally, sample I-170 shows a mixture of emission bands, reflecting the broader thickness distribution in this sample; the emissions come from PNPls with n ≥ 3.