Photoluminescence data were gathered using a custom-made Princeton Instruments spectrometer. An HRS-300 emission monochrometer equipped with three gratings (1200 g mm -1 , 500 nm blaze); 150 g mm -1 , 1200 nm blaze; and 150 g mm -1 , 800 nm blaze) allows collection of Visible-NIR spectra spanning 425 to 1050 nm using a PyLoN 100F Si CCD, and SWIR spectra covering 850 to 1550 nm using a PyLoN IR InGaAs array. Calibration of Vis-NIR spectra relied on an IntelliCal USB-LSVN lamp. SWIR spectra were calibrated with a Princeton Instruments SWIR quartz tungsten halogen lamp with a builtin 850 nm long-pass filter. A double monochrometer system (HRS 500) provides tunable monochromatic excitation by filtering the output of an Energetiq EQ99x laser-driven light source. This system generates typical full width at half maximum (FWHM) excitation bandwidths of ≤16 nm using a 1200 g mm -1 , 750 nm blaze excitation grating. Exposure times ranged between 0.5 to 1 s, while detection slit widths varied from 0.25 to 1 mm. Photoluminescence spectra for NH 3 (CH 2 ) 7 NH 3 ) 2 Sn 3 I 10 was excited at a wavelength of 530 nm using a long pass filter with a cutoff wavelength of 550 nm.