Light Emission Enhancement of (C3H10N)4Pb1-xMnxBr6 Metal-Halide Powders by the Dielectric Confinement Effect of a Nanosized Water Layer

Achieving Ultralong Room-Temperature Phosphorescence in Two-Dimensional Metal Halide Perovskites by Alkyl Chain Engineering

Two-dimensional (2D) metal halide perovskites with highly efficient ultralong room-temperature phosphorescence (URTP) are rare due to their uncertain structures and complicated intermolecular interactions. Herein, by varying the alkyl length of organic units, we synthesized two single-component 2D metal hybrid perovskites, i.e., B-MACC and B-EACC, with obvious URTP emission. In particular, B-EACC exhibits a green-yellow URTP emission with an ultralong lifetime (579 ms) and a high efficiency (14.86%). It is found that the molecular packing of B-EA+ cations because of the presence one more carbon in the alkyl chain affords strong hydrogen bonding and π-π stacking interactions, which immobilizes and reduces the triplet exciton quenching. Moreover, B-MACC and B-EACC with space-time dual-resolved characteristics can be utilized for dynamic information encryption and optical logic gate applications. This study is the first to disclose the relation between the characteristics of molecular packing and the resultant URTP of 2D metal hybrid perovskites, significantly advancing the development of next-generation URTP materials for versatile applications.

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.

Temperature-Dependent Reversible Optical Properties of Mn-Based Organic-Inorganic Hybrid (C8H20N)2MnCl4 Metal Halides

Organic-inorganic metal halides (OIMHs) have abundant optical properties and potential applications, such as light-emitting diodes, displays, solar cells, and photodetectors. Herein, we report zero-dimensional Mn-based OIMH (C₈H₂₀N)₂MnCl₄ single crystals synthesized by a simple slow evaporation method, which exhibit intense green emission at 520 nm originating from ⁴T₁-⁶A₁ transition of Mn²⁺ ions. Large organic cations in the crystal structure result in the isolated [MnCl₄]^2- tetrahedrons, and the closest Mn-Mn distance reaches 9.07 Å, which effectively inhibits the migration of excitation energy between adjacent Mn²⁺ emission centers, thus achieving a high quantum yield (∼87%) and a long photoluminescence (PL) lifetime (3.42 ms). The different optical and structural properties at low and high temperatures are revealed by temperature-dependent PL and X-ray diffraction spectra. The PL spectra and lifetimes under the heating and cooling processes indicate that the optical property transitions are reversible at 220/240 K. Our work provides a promising strategy for building multifunctional optoelectronic materials and insights into the understanding convertible photophysical properties from isomers of metal halides.

Self-trapped excitons in soft semiconductors

Self-trapped excitons (STEs) have attracted tremendous attention due to their intriguing properties and potential optoelectronic applications. STEs are formed from the lattice distortion induced by the strong electron (exciton)-phonon coupling in soft semiconductors upon photoexcitation, which features in broadband photoluminescence (PL) emission spectra with a large Stokes shift. Recently, significant progress has been achieved in this field but many remain challenges that need to be solved, including the understanding of the underlying physical mechanism, tuning of the performance, and device applications. Along these lines, for the first time, systematic experimental characterizations and advanced theoretical calculations are presented in this review to shed light on the physical mechanism. The possibility of tuning the STEs through multiple degrees of freedom is also presented, along with an overview of the STE-based emerged applications and future research perspectives.

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

Low-dimensional metal halides are attractive for applications in photodetectors, solid-state lighting, and solar cells, but poor stability is an obstacle that must be overcome in commercial applications. Herein, we successfully synthesized a Ruddlesden-Popper (RP)-phased perovskite Mn²⁺:Cs₃Cd₂Cl₇ with high photoluminescence quantum yield (PLQY) and outstanding thermal and environmental stability by a solvothermal method. The pristine sample Cs₃Cd₂Cl₇ exhibits a weak cyan broad emission centered at 510 nm with a low PLQY of ∼4%. Once Mn²⁺ ions are introduced into the host lattice, a bright orange emission peaking at 580 nm with a high PLQY of ∼74% was achieved, which is attributed to the efficient energy transfer from the host to Mn²⁺ ions and thus results in the ⁴T₁ → ⁶A₁ radiation transition of Mn²⁺ ions. The photoluminescence (PL) intensity and environmental stability of Mn²⁺:Cs₃Cd₂Cl₇ can be further improved through A-site Rb alloying. Finally, an orange LED with outstanding color stability was fabricated on the basis of the Mn²⁺:Cs₃Cd₂Cl₇. Our work successfully elucidates that dopant plays an integral role in tailoring optical properties.

Organo-Metal Halide Scintillator with Weak Thermal Quenching Up to 200 °C

The prominent thermal quenching (TQ) effect of organic-inorganic metal halides limits their applications for lighting and imaging. Herein, we report an organo-metal halide scintillator (TTPhP)₂MnCl₄ (TTPhP⁺ = tetraphenylphosphonium cation), which exhibits a weak TQ effect up to 200 °C under ultraviolet-visible light (efficiency loss of 5.5%) and X-ray radiation (efficiency loss of 37%). The light yield of the (TTPhP)₂MnCl₄ scintillator (37 000 photons MeV^-1 at 200 °C) under X-ray radiation is >2 times that of the commercial scintillator LuAG:Ce (15 000 photons MeV^-1 at 200 °C). The microscopic mechanism of the weak TQ effect is demonstrated to be the scintillator having the ability to compensate for the emission losses from trapped charges and the large Mn-Mn distance (10.233 Å) suppressing nonradiative recombination at high temperatures. We further demonstrate the applications of (TTPhP)₂MnCl₄ as high-power white-light-emitting diodes operated at currents of ≤300 mA and X-ray imaging at 200 °C with a high spatial resolution.