Pressure-Induced Structural and Optical Transitions in Luminescent Bulk Cs₄PbBr₆

Abstract

Low-dimensional metal halide compounds, usually described as low-dimensional perovskites, present exciting properties as functional materials for a broad range of optoelectronic applications. These compounds are characterized by intense photoluminescence (PL), a narrow emission line width, and a high exciton binding energy. In particular, the mechanism behind the strong green emission of the zero-dimensional compound Cs 4 PbBr 6 has been the subject of intense debate. As a propertytuning tool, hydrostatic pressure was used to investigate the structural and optical properties of bulk Cs 4 PbBr 6 through synchrotron X-ray diffraction combined with Raman and PL spectroscopies. As a result, two structural phase transitions at 3.2 and 4.6 GPa were identified, with the latter not observed in previous investigations performed on nanocrystals. Also, the pressure dependence of the PL emission was recorded and compared with the previous results on Cs 4 PbBr 6 and CsPbBr 3 nanocrystals. Under the ambient conditions, strong green emission exhibits a subtle redshift, followed by a blueshift under pressure, being associated first with an intensity enhancement and subsequent quenching above 3 GPa. These results support the CsPbBr 3 luminescent inclusions as the PL emission mechanism in Cs 4 PbBr 6 .

Exciton–phonon coupling in alanine-based hybrid lead bromide

“…While the mode at 123 cm −1 to the Br–Pb asymmetric stretching, ν as (Br–Pb). 77,106–108 The same active vibrational modes were observed in our ATR-FTIR analysis (see Fig. S3 in the ESI†) and are in good agreement with the previously reported study by Sirenko et al 63 Thus, the corresponding phonon at 115 cm −1 that couples with excitons is close in energy to the Pb–Br phonon observed in our Raman spectrum in the range of 80–140 cm −1 , as shown in Fig.…”

“…First, the low wavenumber range (50–300 cm −1 ) corresponds to [PbBr 6 ] −4 octahedral modes mixed with the organic cation [(NH 3 )–(CH 2 ) 2 –COOH] lattice modes (Fig. 6(a)); 77,92,105 and, a second range, beyond 300 cm −1 , in which we observe the organic molecule internal modes (Fig. 6(b and c)).…”

“…It is important to clarify this point because, usually, the optical properties of hybrid halide perovskite-like compounds are very sensitive to size processing. 75–78 Additionally, a step followed by a tail around 480 nm, which presents a lower intensity concerning the other peaks, could be attributed to another lower energy substrate. However, when we applied the Tauc Plot method, it did not present enough intensity to estimate the bandgap, therefore being disregarded in our discussions.…”

Tailoring Molecular Dimensions of Cesium Lead Bromide Perovskites with Varying Compositions of Oleic Acid and Oleylamine

“…Due to a high exciton binding energy (171 meV), [39] the PL of Cs 4 PbBr 6 powder is insensitive to environmental humid and air, and can be maintained in an observation period of 3 months. The origin of the PL emission of Cs 4 PbBr 6 is controversial: [37] some researchers thought that the luminescence of Cs 4 PbBr 6 arose from embedded trace amounts of 3D CsPbBr 3 ; [40][41][42][43] while the others argued that the defects (such as Br vacancy) in Cs 4 PbBr 6 were the luminescent centers. [34,39,44] XRD patterns do not show the presence of a 3D phase in this work.…”

Zero-dimensional mixed-cation hybrid lead halides with broadband emissions

“…The most famous are all-inorganic Cs 4 PbX 6 compounds, composed of isolated PbX 6 octahedra surrounded by Cs + ions. 13,23,[25][26][27] PL was reported for Cs 4 PbBr 6 but it consisted of a relatively narrow green emission. 13,23,[25][26][27] Therefore, its mechanism is still controversial and some reports attributed it to CsPbBr 3 impurities, inclusion-induced emission or defect state-induced emission.…”