Fig. 2: Bulk FAPbI₃ thin films exhibit isolated sites of quantum emission with extremely narrow linewidths.

a–e, Hyperspectral wavelength-selective PL maps of solution-processed FAPbI₃ films, obtained at 5K using an excitation wavelength of 405 nm and an excitation power of ~1.8 mW cm⁻², which exhibit individual emission spots at wavelengths of 660 nm (a), 686 nm (b), 706 nm (c), 718 nm (d) and 736 nm (e). Scale bar, 10 µm. The map is recorded from a fixed region of the film, and the wavelength of the individual map is denoted on each panel. The individual spots appear at different positions when the map is displayed at changing wavelengths (see also Supplementary Video 1). The colour scale denotes the PL intensity. The dashed circles indicated by arrows mark the locations where the PL spectra are acquired. f–j, PL spectra showing the emission peaks with extremely narrow FWHM values at the individual spots denoted by the white dashed circles in PL maps a (f), b (g), c (h), d (i) and e (j). The dashed cyan lines denote the region-selected TA peaks, of which the original data are normalized to unity. The TA and PL peaks show a precise match.