Figure shows the single and multiphoton excited photoluminescence spectra of each sample. The marked peak positions for each sample are summarized in Table . The PL spectra peak at ∼ 1.99 eV (623 nm) and ∼ 2.14 eV (579 nm) for the n = 2 and n = 3 variants, respectively. These values are similar to the ∼ 2.01 eV and ∼ 2.12 eV peaks previously reported for the n = 2 and n = 3 BA variants. All of the mPL spectra peak positions are redshifted by ∼ 0.1 eV from the PL peak positions. A similar redshift has been reported for 3D (MA)PbI 3 and BA 2D perovskites. We Figure : Multidimensional harmonic generation for six (RNH 3 ) 2 (MA) n-1 Pb n I 3n+1 2D-RP perovskite samples. x-axis is monochromator setpoint (emission color), y-axis is excitation laser setpoint, and colormap (in logarithmic scale, shown on the right hand side) corresponds to measured output intensity. Columns and rows correspond to n and RNH 3 permutations, respectively. Blue overlines indicate the SHG emission frequency. The excitation laser has a smooth variation in its spectrum which is maximized at ω ≈ 0.96 eV with a fluence of ∼1400 µJ/cm 2 -this variation is not corrected for in these spectra. Gray pixels indicate values which are negative and therefore unable to be represented on a logarithmic scale. These pixels characterize the noise floor of our measurement.