Fast Intrinsic Emission Quenching in Cs4PbBr6 Nanocrystals.

Urko Petralanda,Roman Krahne,Dmitry Baranov,Giulia Biffi,Simon C Boehme,Ivan Infante,Liberato Manna

doi:10.1021/acs.nanolett.1c02537

Urko Petralanda, Roman Krahne + Show 5 more

Open Access

https://doi.org/10.1021/acs.nanolett.1c02537

Copy DOI

Abstract

Cs4PbBr6 (0D) nanocrystals at room temperature have both been reported as nonemissive and green-emissive systems in conflicting reports, with no consensus regarding both the origin of the green emission and the emission quenching mechanism. Here, via ab initio molecular dynamics (AIMD) simulations and temperature-dependent photoluminescence (PL) spectroscopy, we show that the PL in these 0D metal halides is thermally quenched well below 300 K via strong electron–phonon coupling. To unravel the source of green emission reported for bulk 0D systems, we further study two previously suggested candidate green emitters: (i) a Br vacancy, which we demonstrate to present a strong thermal emission quenching at room temperature; (ii) an impurity, based on octahedral connectivity, that succeeds in suppressing nonradiative quenching via a reduced electron–phonon coupling in the corner-shared lead bromide octahedral network. These findings contribute to unveiling the mechanism behind the temperature-dependent PL in lead halide materials of different dimensionality.

Highlights

Cs4PbBr6 (0D) nanocrystals at room temperature have both been reported as nonemissive and green-emissive systems in conflicting reports, with no consensus regarding both the origin of the green emission and the emission quenching mechanism
Speculations of an intrinsic emission of the material[6,16,17] gradually sedimented into two main lines of interpretation; i.e., the emission has been assigned to either deep band levels induced by point defects, likely Br vacancies,[16−21] or to embedded nanoscale inclusions of, e.g., CsPbBr3 (3D)[7,12,22−27] or lower-dimensional structures,[28] whose small size evades facile characterization, e.g., via
We present an ab initio molecular dynamics t(eAmIMpeDra)tursetsu, dfyromof34buKlktoCrso4oPmbBtre6mpineraaturwe i(d3e00raKn)g.3e0−o36f We demonstrate that strong electron−phonon coupling is responsible for fast nonradiative decay in the pure 0D structure already at temperatures well below 300 K

Summary

Experimental PL Excitation and Emission Spectra of

These results lead for several conclusions: (a) the good agreement between experiment and theory lends credibility to the employed computational framework; (b) the similarity to a proportionality to the square root of the temperature (dashed line in Figure 4c) is consistent with the expected temperature dependence for the simple displaced harmonic-oscillator model employed to deduce the nonradiative quenching rates (Figure 3); (c) the more than four times larger PL fwhm in Cs4PbBr6 compared to CsPbBr3 (gray open circle) is a clear manifestation of the large exciton−phonon coupling in Cs4PbBr6.

■ ACKNOWLEDGMENTS

■ REFERENCES