Exciton-phonon interactions in the Cs₃Bi₂I₉crystal structure revealed by Raman spectroscopic studies

Abstract

The enhancement of the Raman scattering in Cs3Bi2I9 is evaluated by the ratio IT/I300 K between the relative intensities of the Raman line peaked at 146 cm−1, when the spectra are recorded in the temperature range of 88–300 K, as a signature of exciton–phonon interactions. In the resonant and nonresonant conditions, excitation wavelengths 476, 561, and 660 nm, respectively, are used in order to overlap with great accuracy the bands disclosed by diffuse reflection, photoconductivity (PC), photoluminescence (PL), and photoluminescence excitation (PLE) spectra. Based on the experimental analyses, the strength of exciton–phonon interaction is dependent on the defects in the crystal and the type–range interaction of the excitations in an independent Bi2I93− cluster. The noticeable PL band, attributed to excitons trapped on different stacking faults, manifests some defects in crystal that diminish the movement of excitons. This effect significantly decreases the overlaps of excitons with the phonons, resulting in a reduced exciton–phonon coupling.

Green solvent assisted synthesis of cesium bismuth halide perovskite nanocrystals and the influences of slow and fast anion exchange rates

“…The dominant vibrations in the crystalline lattice of Cs 3 Bi 2 I 9 arise from the strong bonds of the [Bi 2 I 9 ] 3À sub-unit and the weaker modes arise from the ionic interactions of that sub-unit with the bridging Cs + cations (Table S1 in ESI †). 51,53,54 The peak positions within the Raman spectra of the Cs 3 Bi 2 Br 9 and Cs 3 Bi 2 Cl 9 NCs were also in agreement with the data previously reported for larger Cs 3 Bi 2 Br 9 and Cs 3 Bi 2 Cl 9 crystals. 52 The optical properties of the Cs 3 Bi 2 X 9 NCs were investigated as colloidal suspensions under ambient conditions to evaluate their excitation and PL response.…”

Bandgap engineering of a lead-free defect perovskite Cs3Bi2I9through trivalent doping of Ru3+

“…5c) can be deduced for Cs 3 Bi 2Àx Ru x I 9 with increasing Ru 3+ doping. The bandgap value of pristine Cs 3 Bi 2 I 9 is in good agreement with previous reports, [34][35][36] and the shi of bandgaps is consistent with the optical color change observed for these compounds.…”

Pb-Free Cs3Bi2I9 Perovskite as a Visible-Light-Active Photocatalyst for Organic Pollutant Degradation

“…The UV-Vis diffuse reflectance spectrum of the as-synthesized perovskite was recorded with a Cary-100 Bio Spectrophotometer (Agilent, Santa Clara, CA, USA), equipped with an integrating sphere, at room temperature, within a wavelength range between 300 and 800 nm, and employing barium sulfate as the reflection standard. The optical bandgap energies were investigated using the Kubelka-Munk function [33]. The specific surface area of the sample was evaluated with Brunauer-Emmett-Teller (BET) measurements.…”

“…Bismuth is known as an abundant metal on the earth's crust; it can be recovered as a byproduct of other metals' refining, and its price is quite stable and relatively low [30]. Several scientists have investigated ternary cesium bismuth halide (Cs 3 Bi 2 I 9 ) as a new material for high-performance photovoltaic applications [27,[31][32][33][34]. The Cs 3 Bi 2 I 9 structure consists of identical perovskite-like fragments described by a general formula A 3 Bi 2 I 9 , with alternating edge-sharing [BiI 6 ] 3− octahedral layers, where the voids are filled with Cs + cations [35,36].…”

“…The tuneable structure and morphology have a great influence on the intrinsic electronic and optical properties that make this material so interesting in photocatalytic applications [37]. Many pioneers in photovoltaic technology have already experienced its advantages, such as excellent photoluminescence intensity suppression and significantly less toxicity than lead halides [31,33,34,[37][38][39][40][41][42]. Intense research has been reported on Cs 3 Bi 2 I 9 due to its attractive and impressive optical and electronic properties, such as excellent carrier transport behavior, high defect tolerance, and extremely low-density defects.…”