Temperature-Dependent Photoluminescence of Cesium Lead Halide Perovskite Quantum Dots: Splitting of the Photoluminescence Peaks of CsPbBr₃ and CsPb(Br/I)₃ Quantum Dots at Low Temperature

Abstract

We investigated the temperature-dependent photoluminescence (PL) properties of colloidal CsPbX 3 (X = Br, I, and mixed Br/I) quantum dot (QD) samples in the 30−290 K temperature range. Temperature-dependent PL experiments reveal thermal quenching of PL, blue shifting of optical band gaps, and line width broadening for all CsPbX 3 QD samples with increasing temperature. Interestingly, side-peak emissions that are spectrally separated from the excitonic PL peaks were observed for both CsPbBr 3 and CsPb(Br/I) 3 QD samples at temperatures below ∼250 K. The side-peak emission for the CsPbBr 3 QD sample is located at a lower energy compared to the band-edge peak, whereas that of the Br-rich CsPb(Br/I) 3 alloy QD sample is located at a higher energy than that of the band-edge peak. We found that the CsPbBr 3 QDs have two emissive states, a band-edge state, and one involving shallow defects, which can be spectrally separated by narrowing the emission line widths at low temperature. In the case of the Br-rich CsPb(Br/I) 3 QD sample, the partial halide-segregation-induced heterogeneity of the alloy phase within the ensemble at low temperature leads to blue-shifted radiative recombination channels.

Investigation of the Role of the Environment on the Photoluminescence and the Exciton Relaxation of CsPbBr3 Nanocrystals Thin Films

“…The line shape can be well reproduced by a best fit with two Gaussian bands peaked at 2.3873 and 2.405 eV and with a FWHM of 149 and 50 meV, respectively. Similar spectra have been reported in the literature for CsPbBr 3 NCs films, ascribing the broad band at low energy to excitons bound to defects (BE) and the narrow band at higher energy to free excitons (FE) [30,31] The PL intensity presents a quite stable value during continuous laser irradiation (see Figure 3a) with signal variation within 3% around the average values. When the sample atmosphere is changed from V to WA, we observe (see inset of Figures 2a and 3a) an intensity increase by a factor 1.3 (about 30%), and the signal attests itself to the new value within the WA recovering time (less than 5 s).…”

Low‐Temperature Absorption, Photoluminescence, and Lifetime of CsPbX3 (X = Cl, Br, I) Nanocrystals

“…Unlike single crystals, NCs may show an inhomogeneous linewidth due to variable environments (frequently observed as spectral diffusion in single particle measurements) and size dispersion, arising from quantum confinement effects, although these are expected to be weak for the NCs measured here . We do not observe any clear secondary features or shoulder of the PL at any temperature, despite earlier reports . Thermal broadening of PL at higher temperatures, plotted in Figure b, is accounted for using a Voight fit.…”

Synthesis and Localized Photoluminescence Blinking of Lead‐Free 2D Nanostructures of Cs3Bi2I6Cl3 Perovskite

“…E B signifies the exciton binding energy for excitons to obliterate by the non‐radiative trap states, in which the larger value is favourable for excitonic stabilization and for proficient PL. The value E B of Cs 3 Bi 2 I 6 Cl 3 NCs is estimated to be 69.90 meV from the linear plot of ln ( I 0 / I T ) and 1/ k B T (Figure S7b, SI), which is comparable with the earlier reported MA 3 Bi 2 I 9 (MA=methylammonium), but larger than that of the 3D CsPbX 3 NCs (≈15–50 meV) . The E B value of ≈70 meV is found to be higher than that of thermal ionization energy (≈26 meV), which confirmed the existence of excitons well above the room temperature, and further emphasized the prospective use of this material in exciton‐associated optoelectronic devices …”