Efficient Orange Emission in Mn2+-Doped Cs3Cd2Cl7 Perovskites with Excellent Stability

Unveiling Doping Kinetics in Cu(I) Metal Halides for Customized Luminescent Performance

Intentional doping plays a pivotal role in customizing metal halides' electronic and optical features. This work manipulates the incorporation and distribution of Mn2+ in Cu(I) halide by controlling the elemental steps involved in the growth-doping kinetics as well as investigates the localized lattice and electronic structures in different doping configurations. Complementary experimental and theoretical results demonstrate that a uniform and relatively high Mn2+ doping level can be achieved by a step-tailored strategy that encompasses reducing the growth rate of the halide matrix, enhancing the surface adsorption of Mn2+, and facilitating the incorporation of the dopants. The optimized doping configuration mitigates severe lattice distortion and decreases the non-radiative transition rate, resulting in explicit dual-band emission and an enhanced photoluminescence quantum yield. This work underscores an effective synthesis strategy to harness the full potential of Mn2+-doped metal halides beyond Cu(I)-based ones and also showcases a new working paradigm of separately controlling the doping procedures for obtaining metal halides with customized optical/optoelectronic properties.

Dual-emissive luminescence in OIHMH single crystals: tunable red-green emissions via Mn2+ doping and theoretical insights

The burgeoning demand for materials with tunable photoluminescence properties for applications has necessitated the exploration of novel luminescent materials. This study presents the synthesis and characterization of a novel 0D organic-inorganic hybrid metal halide (OIHMH) single crystal, C6H14N2CdBr4, which exhibits intriguing luminescent properties upon Mn2+ doping. The introduction of single Mn2+ ions results in a dual-emission, with the unexpected emergence of a red emission peak at 627 nm, in addition to the conventional tetrahedral green emission at 525 nm. This dual-emission is attributed to the distinct inter-tetrahedral distances within the crystal structure of C6H14N2CdBr4 with varying distances between [CdBr4]2- tetrahedra, influencing the spatial distribution and interaction of the [MnBr4]2- tetrahedra. Electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations reveal the 627 nm and 525 nm emissions are attributed to the d-d transition of magnetic coupled Mn2+-Mn2+ pairs and isolated Mn2+ ions, respectively. This study not only advances the understanding of the luminescence mechanisms of Mn2+ but also paves the way for the development of tunable luminescent materials.

Structural Transformation and Photoluminescent Property of Manganese-Doped Bismuth-Based Perovskites

Here, we synthesized pure Cs₃Bi₂Cl₉ (CBC) and manganese (Mn)-doped crystals with different feeding ratios, leading to changes in structure and luminescence. The crystals Cs₃Bi₂Cl₉-Mn (CBCM) formed by doping a minor amount of Mn²⁺ (Bi/Mn = 8:1) maintain the orthorhombic phase structure of the host, but when Bi/Mn = 2:1, the crystal structure is more inclined to form Cs₄MnBi₂Cl₁₂ (CMBC) of a trigonal phase. Combined with density functional theory (DFT) calculation, the results demonstrate that a moderate amount of Mn²⁺ doping can create impurity energy levels in the forbidden band. However, as the structure transitions, the type of energy band structure changes from indirect to direct, with completely different electronic orbital features. Temperature-dependent time-resolved and steady-state photoluminescence spectroscopies are used to explore the structure-related thermal properties and transitional process. Differences energy transfer routes are revealed, with CBCM relying on intersystem energy transfer and CMBC mainly depending on direct excitation of Mn²⁺ to produce d-d transitions. Furthermore, since CMBC is temperature-sensitive, we perform the first photoluminescent (PL) lifetime temperature measurement using CBMC and obtain a maximum relative sensitivity of 1.7 %K^-1 and an absolute sensitivity of 0.0099 K^-1. Our work provides insight into the mechanism of Mn²⁺ doping-induced luminescence and offers a potentially effective doping strategy for improving the PL properties of lead-free metal halide perovskites.

Luminescence and Mechanism of Mn2+ Substitution in Cs7Cd3Br13 with Two Types of Coordination Number

Cadmium-based perovskite materials as promising optoelectronic materials have been widely explored, but there are still some special microscopic interaction-dependent properties not fully understood. Here, we successfully synthesized Cs₇(Cd_1-XMn_X)₃Br₁₃ crystal by a simple hydrothermal method. In Cs₇Cd₃Br₁₃ crystals with their intrinsic self-trapped exciton (STE) emission, Cd²⁺ ions stay in both different coordination sites, and partial replacement of Cd²⁺ with Mn²⁺ can modify their luminescence properties significantly. The luminescence peak position of the doped sample was adjusted from 610 nm in the undoped sample to 577 nm in the doped one by the combination of STE and Mn d-d transition, with enhanced photoluminescence quantum yield (PLQY) of ∼50% at a Mn precursor ratio of 40%. Their magnetic responses occur from the coexisting ferromagnetic (FM) and antiferromagnetic (AFM) coupling of Mn pairs in four and six coordination sites, modifying its whole emission profile. This material is valuable for studying the structure-optical properties and finding applications in optoelectronic devices.

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

Tailored modifications of halide lead-free perovskites (LFPs) via doping/alloying with metal cations have been recognized as a promising pathway to highly efficient inorganic phosphors with photoluminescence (PL) quantum yields of up to 100 %. Such materials typically display selective sensitivity to UV light, a broad PL range, and long PL lifetimes as well as a unique compositional variability and stability-an ideal combination for many light-harvesting applications. This Minireview presents the state-of-the-art in doped LFPs, focusing on the reports published mostly in the last two to three years. We discuss the factors determining the efficiency and spectral parameters of the broadband PL of doped LFPs depending on the dopant and host matrix, both in micro- and nanocrystalline states, address the most relevant challenges this rapidly developing research area is facing, and outline the most promising concepts for further progress in this field.