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

Unlocking the Potential of Organic-Inorganic Hybrid Manganese Halides for Advanced Optoelectronic Applications

Organic-inorganic hybrid manganese(II) halides (OIMnHs) have garnered tremendous interest across a wide array of research fields owing to their outstanding optical properties, abundant structural diversity, low-cost solution processibility, and low toxicity, which make them extremely suitable for use as a new class of luminescent materials for various optoelectronic applications. Over the past years, a plethora of OIMnHs with different structural dimensionalities and multifunctionalities such as efficient photoluminescence (PL), radioluminescence, circularly polarized luminescence, and mechanoluminescence have been newly created by judicious screening of the organic cations and inorganic Mn(II) polyhedra. Specifically, through precise molecular and structural engineering, a series of OIMnHs with near-unity PL quantum yields, high anti-thermal quenching properties, and excellent stability in harsh conditions have been devised and explored for applications in light-emitting diodes (LEDs), X-ray scintillators, multimodal anti-counterfeiting, and fluorescent sensing. In this review, the latest advancements in the development of OIMnHs as efficient light-emitting materials are summarized, which covers from their fundamental physicochemical properties to advanced optoelectronic applications, with an emphasis on the structural and functionality design especially for LEDs and X-ray detection and imaging. Current challenges and future efforts to unlock the potentials of these promising materials are also envisioned.

Bright Circularly Polarized Mechanoluminescence from 0D Hybrid Manganese Halides

Hybrid metal halides (HMHs) with efficient circularly polarized luminescence (CPL) have application prospects in many fields, due to their abundant host-guest structures and high photoluminescence quantum yield (PLQY). However, CPLs in HMHs are predominantly excited by light or electricity, limiting their use in multivariate environments. It is necessary to explore a novel excitation method to extend the application of chiral HMHs as smart stimuli-responsive optical materials. In this work, an enantiomeric pair of 0D hybrid manganese bromides, [H2(2R,4R)-(+)/(2S,4S)-(-)-2,4-bis(diphenylphosphino)pentane]MnBr4 [(R/S)-1] is presented, which exhibits efficient CPL emissions with near-unity PLQYs and high dissymmetry factors of ± 2.0 × 10-3. Notably, (R/S)-1 compounds exhibit unprecedented and bright circularly polarized mechanoluminescence (CPML) emissions under mechanical stimulation. Moreover, (R/S)-1 possess high mechanical force sensitivities with mechanoluminescence (ML) emissions detectable under 0.1 N force stimulation. Furthermore, this ML emission exhibits an extraordinary antithermal quenching effect in the temperature range of 300-380 K, which is revealed to originate from a thermal activation energy compensation mechanism from trap levels to Mn(II) 4T1 level. Based on their intriguing optical properties, these compounds as chiral force-responsive materials are demonstrated in multilevel confidential information encryption.

Pseudo-2D Layered Organic-Inorganic Manganese Bromide with a Near-Unity Photoluminescence Quantum Yield for White Light-Emitting Diode and X-Ray Scintillator

Eco-friendly lead-free organic-inorganic manganese halides (OIMHs) have attracted considerable attention in various optoelectronic applications because of their superior optical properties and flexible solution processibility. Herein, we report a novel pseudo-2D layered OIMH (MTP)2 MnBr4 (MTP: methyltriphenylphosphonium), which exhibits intense green emission under UV/blue or X-ray excitation, with a near-unity photoluminescence quantum yield, high resistance to thermal quenching (I150 °C =84.1 %) and good photochemical stability. These features enable (MTP)2 MnBr4 as an efficient green phosphor for blue-converted white light-emitting diodes, demonstrating a commercial-level luminous efficiency of 101 lm W-1 and a wide color gamut of 116 % NTSC. Moreover, these (MTP)2 MnBr4 crystals showcase outstanding X-ray scintillation properties, delivering a light yield of 67000 photon MeV-1 , a detection limit of 82.4 nGy s-1 , and a competitive spatial resolution of 6.2 lp mm-1 for X-ray imaging. This work presents a new avenue for the exploration of eco-friendly luminescent OIMHs towards multifunctional light-emitting applications.

Gamma-Ray Irradiation Stability of Zero-Dimensional Cs3Cu2I5 Metal Halide Scintillator Single Crystals

Zero-dimensional Cs₃Cu₂I₅ is one of the most promising metal halide scintillators due to its large Stokes shift, photoluminescence quantum yields, freedom from toxic elements, and excellent energy spectrum resolution. To unlock the full potential of Cs₃Cu₂I₅ as an effective alternative to traditional scintillators for gamma-ray detection, the irradiation stability of Cs₃Cu₂I₅ single crystals under ⁶⁰Co gamma rays with a maximum accumulated dose of 800 krad was explored. Although the luminescence mechanism remained unchanged after irradiation, the optical properties of Cs₃Cu₂I₅ single crystals demonstrated a dose-dependent change at low accumulated doses (<600 krad). However, a further increase in the accumulated dose did not lead to more severe degradation and even slight performance recovery occurred. Electron paramagnetic resonance and theoretical calculation results revealed that the irradiation-induced Cs⁺-related Frenkel defects contribute to performance degradation. These results shed light on the microscopic mechanism of gamma-ray irradiation damage of Cs₃Cu₂I₅ single crystal and provide guidance to their real application.

Highly Luminescent Earth-Benign Organometallic Manganese Halide Crystals with Ultrahigh Thermal Stability of Emission from 4 to 623 K

The phosphor-converted light-emitting diode (PC-LED) has become an indispensable solid-state lighting and display technologies in the modern society. Nevertheless, the use of scarce rare-earth elements and the thermal quenching (TQ) behavior are still two most crucial issues yet to be solved. Here, this work successfully demonstrates a highly efficient and thermally stable green emissive MnI₂ (XanPO) crystals showing a notable photoluminescence quantum yield (PLQY) of 94% and a super TQ resistance from 4 to 623 K. This unprecedented superior thermal stability is attributed to the low electron-phonon coupling and the unique rigid crystal structure of MnI₂ (XanPO) over the whole temperature range based on the temperature-dependent photoluminescence (PL) and single crystal X-ray diffraction (SCXRD) analyses. Considering these appealing properties, green PC-LEDs with a power efficacy of 102.5 lm W^-1 , an external quantum efficiency (EQE) of 22.7% and a peak luminance up to 7750 000 cd m^-2 are fabricated by integrating MnI₂ (XanPO) with commercial blue LEDs. Moreover, the applicability of MnI₂ (XanPO) in both micro-LEDs and organic light-emitting diodes (OLEDs) is also demonstrated. In a nutshell, this study uncovers a candidate of highly luminescent and TQ resistant manganese halide suitable for a variety of emission applications.

Ultrasensitive Optical Thermometry via Inhibiting the Energy Transfer in Zero-Dimensional Lead-Free Metal Halide Single Crystals

Self-referencing optical thermometry based on the fluorescence intensity ratio (FIR) have drawn extensive attention as a result of their high sensitivity and non-invasively fast response to temperature. However, it is a great challenge for luminescent materials to achieve simultaneously high absolute and relative temperature sensitivity based on the FIR technique. Herein, we developed a novel optical thermometer by designing hybrid lead-free metal halide (TTPhP)₂MnCl₄:Sb³⁺ (TTPhP⁺ = tetraphenylphosphonium cation) single crystals with multimodal photoluminescence (PL). The large TTPhP⁺ organic chain resulted in isolated [MnCl₄]^2- and [SbCl₅]^2- in the single crystal, which leads to a negligible energy trasfer process within them. Therefore, the two PL bands (band 1 from [MnCl₄]^2-) with a peak at 518 nm and band 2 (from [SbCl₅]²) with a peak at 640 nm exhibit different thermal-quenching effects, which resulted in excellent temperature sensitivity, with the maximum absolute and relative sensitivities reaching 0.236 K^-1 and 3.77% K^-1 in a temperature range from 300 to 400 K. Both the absolute and relative sensitivities are among the highest values for luminescence thermometry.