Fig. 2.

a Diffuse reflectance spectra of Cs₂AgBiBr₆ and CH₃NH₃PbBr₃. Reproduced with permission from Ref. [48]. b Time-resolved room-temperature PL and fits for the PL decay time (τ) in powder and single-crystal samples. The inset is the photograph of a Cs₂SgBiBr₆ single crystal. Reproduced with permission from Ref. [52]. c Apparent bandgaps of Cs₂AgBiBr₆ and Cs₂(Ag_1−aBi_1−b)TlxBr₆ (x = a + b = 0.075) single crystals extracted by linear fits to α² vs. E (direct gap) and α^1/2 vs. E plots (indirect gap). Reproduced with permission from Ref. [57]. d Photographs of Cs₂AgSbCl₆ and Cs₂AgInCl₆ single crystals (top), and band diagram. A change in the character of the conduction band minimum (CBM) from s orbital derived to p orbital derived while having the valence band maximum (VBM) primarily Ag-d states results in a transition from direct to indirect bandgap. Reproduced with permission from Ref. [59]. e PL spectra of Mn-doped Cs₂AgInCl₆ with different Mn contents, after excitation with 340 nm light. Insets show photographs of luminescence from powder samples under UV light. Reproduced with permission from Ref. [62]. f Photograph of dilute toluene solutions of Cs₂AgBiBr₆, Cs₂AgBiBr_5.2I_0.8, Cs₂AgBiBr_1.6I_4.4 and Cs₂AgBiI₆ nanocrystals. Reproduced with permission from Ref. [51]