New Insights into Mn–Mn Coupling Interaction-Directed Photoluminescence Quenching Mechanism in Mn²⁺-Doped Semiconductors

Abstract

Strong Mn−Mn coupling interactions (dipole− dipole and spin−exchange), predominantly determined by statistically and apparently short Mn•••Mn distances in traditional heavily Mn 2+ -doped semiconductors, can promote energy transfer within randomly positioned and close-knit Mn 2+ pairs. However, the intrinsic mechanism on controlling Mn 2+ emission efficiency is still elusive due to the lack of precise structure information on local tetrahedrally coordinated Mn 2+ ions. Herein, a group of Mn 2+containing metal−chalcogenide open frameworks (MCOFs), built from [Mn 4 In 16 S 35 ] nanoclusters (denoted T4-MnInS) with a precise [Mn 4 S] configuration and length-variable linkers, were prepared and selected as unique models to address the abovementioned issues. MCOF-5 and MCOF-6 that contained a symmetrical [Mn 4 S] core with a D 2d point group and relatively long Mn•••Mn distance (∼3.9645 Å) exhibited obvious red emission, while no room-temperature PL emission was observed in MCOF-7 that contained an asymmetric [Mn 4 S] configuration with a C 1 point group and relatively short Mn•••Mn distance (∼3.9204 Å). The differences of Mn−Mn dipole−dipole and spin−exchange interactions were verified through transient photoluminescent spectroscopy, electron spin resonance (ESR), and magnetic measurements. Compared to MCOF-5 and MCOF-6 showing a narrower/stronger ESR signal and longer decay lifetime of microseconds, MCOF-7 displayed a much broader/weaker ESR signal and shorter decay lifetime of nanoseconds. The results demonstrated the dominant role of distance-directed Mn−Mn dipole−dipole interactions over symmetry-directed spin−exchange interactions in modulating PL quenching behavior of Mn 2+ emission. More importantly, the reported work offers a new pathway to elucidate Mn 2+ -site-dependent photoluminescence regulation mechanism from the perspective of atomically precise nanoclusters.

Design Principles for Enhancing Photoluminescence Quantum Yield in Hybrid Manganese Bromides

“…Crystal structures with larger Mn … Mn distances reduce energy transfer between Mn centers, originating from dipole−dipole interactions and symmetry-directed spin-exchange interactions. 26 The ones with the shortest Mn … Mn distances from 6-8 Å have generally lower PLQYs, where energy transfer occurs more easily over the shorter distances. Other factors that also play a part in determining the PLQY are: (i) The form of the sample (powder samples have lower than single crystals); ((ii) The rigidity of the system (rigid conjugated cations seem to more effectively prevent energy transfer); (iii) Interference from other components in the crystal structure.…”

“…[21][22][23] Hybrid manganese halides are of particular interests for lightemission related applications 24,25 due to their high photoluminescence quantum yields (PLQYs). Mn has also been widely used as a dopant, [26][27][28][29] and is known to effectively give rise to or enhance the PLQY of the host system. 30,31 The emission color of Mn II is highly dependent on the coordination environment of the metal; when it is octahedrally coordinated the emission color is red, 32,33 whereas when it is tetrahedrally coordinated the emission color is green.…”

Discrete Supertetrahedral Tn Chalcogenido Clusters Synthesized in Ionic Liquids: Crystal Structures and Photocatalytic Activity

“…[45,47] As shown in Figure 8a, T4-1-T4-3 -1) exhibits the emission peaking at 611 nm with the full width at half maximum (FWHM) of 75 nm, which could be predominantly assigned to the excitation of Mn 2 + ion. Compared with PL emission peak maxima at room temperature of T4-MnInS-based extended structures, OCF-98-MnInS (618 nm), [97] OCF-99-MnInS (628 nm), [97] MCOF-5 (619 nm) [18] and T4-MnInS (628 nm), [98] a blue shift is observed for that of discrete T4-1.…”

“…Solid-state photoluminescence (PL) of Tn chalcogenido clusterbased compounds has been extensively studied, [16,18,[95][96] while few study was conducted on such discrete clusters synthesized Reproduced from Ref. [48] with the permission from the American Chemical Society.…”

“…All kinds of clusters have been synthesized and studied such as fullerenes, [1][2] noble metal clusters, [3][4] oxide clusters, [5][6] chalcogenide clusters, [7][8] and their mixtures (superatoms). [9][10] The chalcogenido cluster-based compounds have been explored owing to their promising applications in photo/ electrocatalysis, [11][12][13][14] photoelectric effect, [13,15] photoluminescence, [16][17][18] molecular capture, [13,19] fast-ion conductivity [13,20] and ion-exchange. [21][22] Supertetrahedral chalcogenido clusters, as a subclass of chalcogenido clusters, mainly include basic-typed Tn, [23][24] capped-typed Cn, [25][26] and penta-typed Pn [27][28] clusters.…”