Zn²⁺-Doped Lead-Free CsMnCl₃ Nanocrystals Enable Efficient Red Emission with a High Photoluminescence Quantum Yield

Abstract

The toxicity of Pb and the instability of lead halide perovskites are the main obstacles to the practical application of lead-based nanocrystals (NCs). In this paper, all-inorganic Zn2+-doped lead-free perovskite (CsMn1–x Zn x Cl3) NCs were synthesized by a hot-injection method. Mn2+ ions were partially replaced by Zn2+ ions, and the energy transfer between Mn2+ was effectively suppressed. Because of this, excitons are more advantageously confined to the [MnCl6]4– octahedron. Target CsMn0.95Zn0.05Cl3 NCs were endowed with red emission at 654 nm with CIE coordinates of (0.70, 0.30) closing to the standard value of NTSC, and their photoluminescence quantum yield was increased to 77.1%, which is higher than those of Mn-based lead-free perovskites previously reported. Finally, a white light-emitting diode (LED) with adjustable emission from warm to cold white was realized by mixing Cs3MnBr5, CsMn0.95Zn0.05Cl3, and a blue phosphor on a 382 nm ultraviolet LED chip.

Role of CsMnCl3 Nanocrystal Structure on Its Luminescence Properties

“…The binding energy of 100 meV is higher than that of 3D LHPs and comparable to those of all-inorganic 1D lead-free halide perovskites or quasi-2D organic–inorganic hybrid perovskites. − A high E b value indicates strong confinement of the excitons in the r-CsMnCl 3 NCs, which might explain its high PLQY. The fwhm of the emission decreases from 69 to 52 meV when the sample cools down from 293 to 50 K (Figure S7), consistent with the earlier studies on the NCs. , The gradual drop in the fwhm of the NCs with decreasing temperature suggests reduced exciton phonon coupling strength (lattice vibrations), which contributes to the increased integrated PL intensity (Figure c). , …”

“…The temperature-dependent PL quenching of the r-CsMnCl 3 NCs (100–300 K) can be expressed via the following equation I ( T ) = I 0 1 + A .25em normale − E b / k B T where I ( T ) and I 0 are the PL intensities at temperatures T and 0 K, respectively, E b is the exciton binding energy, and k B is the Boltzmann constant. By fitting the PL quenching data using the above equation, an exciton binding energy ( E b ) value of 100 ± 18 meV is extracted (Figure b), which closely matches the earlier reported value (81.36 meV) . The binding energy of 100 meV is higher than that of 3D LHPs and comparable to those of all-inorganic 1D lead-free halide perovskites or quasi-2D organic–inorganic hybrid perovskites. − A high E b value indicates strong confinement of the excitons in the r-CsMnCl 3 NCs, which might explain its high PLQY.…”

“…Guan and co-workers show the PL for the CsMnCl 3 NCs centered at 660 nm with a very low PLQY of 0.7%, 11 which can be partially attributed to the surface traps. Hao et al synthesized the NCs through benzoyl chloride injection and achieved an improved PLQY of 56.3%, 8 which is the consequence of the excess chloride ions provided by the benzoyl chloride. 28,29 Nevertheless, the Cs-oleate injection route employed in this work might be preferable over the one involving hazardous benzoyl chloride when aiming at eco-friendly alternatives to LHP NCs.…”

Doping/Alloying Pathways to Lead‐Free Halide Perovskites with Ultimate Photoluminescence Quantum Yields

“…Similar to the above‐discussed CANIC matrix, partial substitution of Mn 2+ with Zn 2+ cations in the nanocrystalline CsMnCl 3 host resulted in efficient spatial confinement of MnCl 6 octahedra, thus prohibiting energy migration between Mn‐based centers and boosting STE PL QY up to ca. 77 % [42] …”

Dotierungs‐/Legierungswege zu bleifreien Halogenid‐Perowskiten mit ultimativen Photolumineszenz‐Quantenausbeuten

“…77 % erhöht wurde. [42] Eine starke Verzerrung des BHP-Gitters durch "fremde" Liganden kann ebenfalls zu bemerkenswerten Veränderungen der spektralen STE-PL-Parameter führen, wie für das Sb-dotierte Paar Rb 3 InCl 6 /Rb 2 InCl 5 (H 2 O) gezeigt wird. [28] Je nach der Bindung des "fremden" Liganden an die M III -Stelle kann diese Veränderung reversibel sein und eine zusätzliche Kontrolle über die PL-Farbe ermöglichen.…”