Fundamental optical absorption of Cs4PbCl6

Abstract

The fundamental absorption spectrum of Cs4PbCl6 has been observed for the first time. The spectrum exhibits novel structures. They are explained in terms of Pb2+-ion excitation of the octahedral Pb2+(Cl-)6 quasi-complexes, like the case of isolated Pb2+ ions, doped in fcc alkali halides. The individual quasi-complexes behave like quantum dots. The Cs4PbCl6 crystal provides the regular array of the quantum dots

Unveiling the Excited‐State Dynamics of Mn2+ in 0D Cs4PbCl6 Perovskite Nanocrystals

“…The emission band at 358 nm agreed well with that of Pb 2+ emission in Cs 4 PbCl 6 perovskites previously reported and can be assigned to the electronic transitions of Pb 2+ from 3 P 0,1 levels to 1 S 0 level. [ 8,11b ] The emission band at 617 nm was ascribed to the spin‐forbidden 4 T 1g → 6 A 1g transition of Mn 2+ occupying the octahedral Pb 2+ sites, as well documented in Mn 2+ ‐doped CsPbCl 3 NCs. [ 7a–c ] The PL intensity of Mn 2+ increased gradually at the expense of that of Pb 2+ with increasing the Mn 2+ concentration, indicative of an efficient energy transfer from Pb 2+ to Mn 2+ in Cs 4 PbCl 6 :Mn 2+ NCs, [ 8 ] as also evidenced by the nearly same exciton excitation band of Pb 2+ at 289 nm for the Pb 2+ and Mn 2+ emissions at 358 and 617 nm, respectively (Figure S6, Supporting Information).…”

“…All the NCs displayed an intense and narrow absorption band (full width at half maximum (FWHM) ≈172 meV) at 284 nm (4.37 eV), which is independent of Mn 2+ doping concentration and is attributed to the localized exciton absorption of Cs 4 PbCl 6 originating from the spin‐orbital allowed 1 S 0 ( 1 A g ) → 3 P 1 ( 3 T 1u ) transition of Pb 2+ in isolated [PbCl 6 ] 4− octahedra. [ 11 ] The essentially identical exciton absorption band in Mn 2+ ‐doped Cs 4 PbCl 6 NCs with varying Mn 2+ concentrations suggests that Mn 2+ doping has little influence on the electronic structure of Cs 4 PbCl 6 host; this differs from that of Mn 2+ ‐doped CsPbCl 3 where Mn 2+ doping resulted in a blueshift in the exciton absorption band edge due to the effect of Mn 2+ alloying on the bandgap of CsPbCl 3 . [ 7a ] No absorption tail was observed in the spectral range from 350 to 450 nm, affirming that the NCs were free of CsPbCl 3 impurity.…”

Nearly Monodisperse Insulator Cs4PbX6 (X = Cl, Br, I) Nanocrystals, Their Mixed Halide Compositions, and Their Transformation into CsPbX3 Nanocrystals

“…21 Finally, in the A 4 PbX 6 structure (A = Rb + , Cs + ), the PbX 6 4– octahedra are completely decoupled in all dimensions (Figure 1b), 22−26 and the optical properties of such crystals closely resemble those of individual [PbX 6 ] 4– clusters that have been observed experimentally in halide salts doped with Pb 2+ ions. 14,15 This results in insulator band gaps (Cs 4 PbCl 6 = 4.37 eV, Cs 4 PbBr 6 = 3.95 eV, and Cs 4 PbI 6 = 3.38 eV), 23−27 and the A 4 PbX 6 phase is thus often referred to as a zero-dimensional (0D) perovskite. While the 3D and 2D phases of LHPs are widely studied and well understood, 0D perovskites are comparatively less explored with only very recent works revisiting the optical properties of Cs 4 PbBr 6 powders and single crystals.…”

Zero-Dimensional Cesium Lead Halides: History, Properties, and Challenges

“…2 Indeed, the reported bandgaps are all in the UV region, with Cs 4 PbCl 6 = 4.37 eV, Cs 4 PbBr 6 = 3.95 eV, and Cs 4 PbI 6 = 3.38 eV, as shown in Figure 1c. 3,6,8,9 The decoupled [PbX 6 ] 4– octahedra in Cs 4 PbX 6 , compared to the halide-coupled [PbX 6 ] 4– octahedra in LHP, cause the bandgap of Cs 4 PbX 6 to shift toward values of free [PbX 6 ] 4– clusters in solutions and essentially lead to single molecule-like, excitonic absorption bands. 13,16,29 The fact that Cs 4 PbX 6 phases have bandgap values close to their respective free [PbX 6 ] 4– clusters is also evident from the optical properties of a series of alkali metal halides (AX, A = Na, K, Rb, Cs; X = Cl, Br, I) doped with Pb 2+ .…”