Efficient Emission in Halide Layered Double Perovskites: The Role of Sb³⁺ Substitution in Cs₄Cd_1–xMn_xBi₂Cl₁₂ Phosphors

Abstract

Layered halide perovskites and double perovskites optoelectronic properties have recently been the subject of intense research. Layered double perovskites represent the merging of both worlds, and as such, have the potential to further expand the already vast space of optoelectronic properties and applications of halide perovskites. Despite having more than 40 known members, to date, only the <111>-oriented layered double perovskites: Cs4Cd1-xMnxBi2Cl12, have shown efficient photoluminescence (PL). In this work, we replaced Bi with Sb to further investigate the electronic structure and PL properties of these materials, resulting in two new families of layered inorganic perovskites alloys with full solubility. The first family, Cs4Cd1-xMnSb2Cl12, exhibits a PL emission at 605 nm ascribed to Mn 2+ centers in octahedral coordination, and a maximum photoluminescence quantum yield PLQY of 28.5%. The second family of alloys, also with full solubility, Cs4Cd0.8Mn0.2(Sb1-yBiy)2Cl12, contains a fixed amount of Mn 2+ and Cd 2+ cations but different concentrations of the trivalent metals. This variability allows the tuning of the PL emission from 603 nm to 614 nm. We show that the decreased efficiency of the Cs4Cd1-xMnxSb2Cl12family compared to Cs4Cd1-xMnxBi2Cl12, is mostly due to a decreased spin-orbit coupling in Sb and the subsequent increased electronic delocalization compared to the Bi alloys, reducing the energy transfer to Mn 2+ centers. This work lays out a roadmap to understand and achieve high photoluminescence efficiencies in layered double perovskites.

Red-Emissive Nanocrystals of Cs4MnxCd1-xSb2Cl12 Layered Perovskite

“…The observed behavior is consistent with the corresponding bulk material except for the intensity variation and shift of the last feature (250 -300 nm), that was not previously observed by the Solis -Ibarra's group. 19 Overall, the absorption spectrum of Cs4MnxCd1-xSb2Cl12 seems to be mostly determined by transitions related to Sb 3+ , not unlike previous observations on Cs3Sb2Cl9. 24 Sb 3+ is a ns 2 ion characterized by the 1 S0 ground state and four higherenergy levels denoted as 3 P0, 3 P1, 3 P2 and 1 P1.…”

“…Similar results were reported for the corresponding bulk system. 19 However, we observed a red shift of the PL peak related to the increasing amount of Mn 2+ (Figure 2d). With increasing Mn 2+ concentration the emission gradually shifts from 624 nm (6% Mn 2+ ), a value higher than in bulk Cs4MnxCd1-xSb2Cl12 but close to reports for the Bi-based counterpart Cs2MnBi2Cl12, 20,22 to a roughly constant spectral position of ~648 nm for x > 0.5.…”

“…25 The absorption in the 300 -400 nm span can be ascribed to the partially allowed 1 S0 → 3 P1 transition, commonly named as the A band, split into a doublet; similarly, the allowed 1 S0 → 1 P1 transition (Cband) is responsible for the absorption signal found at ~ 270 nm. 11,19,25 Instead, the d → d Mn 2+ transition, generally observed for Mn-based materials between All the Cs4MnxCd1-xSb2Cl12 compositions, except for x = 0, show a red emission centered at around 620-650 nm under UV excitation S6b). The photoluminescence excitation (PLE) shape spectra exhibit an intense peak centered at ~325 nm with a shoulder at ~285 nm (Figure 2b).…”

“…These results agree with the data reported on the corresponding powders. 19 Transmission electron microscopy (TEM) micrographs of Cs4MnxCd1-xSb2Cl12 NCs evidenced the formation of NCs with a cuboidal shape (Figure 1c-e) and a mean size of ∼10.6 nm when employing an amount of Mn 2+ up to 80% (x = 0.8). For the larger Mn 2+ fractions (x = 0.9, 1) we observed a smoothening of the cuboidal edges (Figures 1e and S4).…”

“…18 A more efficient emission has been observed with the partial introduction of Cd 2+ , leading to a photoluminescence quantum yield (PLQY) of 28.5% for Cs4Cd0.8Mn0.2Sb2Cl12. 19 The replacement of Sb 3+ with Bi 3+ resulted in an increase of the PLQY 20 up to 79.5% for the composition Cs4Cd1-xMnxBi2Cl12 (x =0.1). 21 H. Yang et al successfully synthesized the same stoichiometry series in the form of nanocrystals; however, the resulting materials showed a 20fold drop of the PLQY (4.6%) compared to bulk crystals.…”