Efficient and Reabsorption-Free Radioluminescence in Cs3Cu2I5 Nanocrystals with Self-Trapped Excitons

CsCu2I3 Nanocrystals: Growth and Structural Evolution for Tunable Light Emission

CsCu₂I₃ mixed with Cs₃Cu₂I₅ has shown potential applications as white-light-emitting materials, while their growth, structural evolution behaviors, and their impact on photoluminescence of CsCu₂I₃ nanocrystals (NCs) are still not known. In this work, we investigated the growth and structural evolution of CsCu₂I₃ nanocrystals with increasing reaction temperature. At low temperature and in the presence of a high dosage of oleic acid and oleylamine, Cs₃Cu₂I₅ nanoparticles, rather than CsCu₂I₃ NCs, preferred to form in the hot-injection reaction system. Increasing the reaction temperature promoted the formation of CsCu₂I₃ nanorods. Phase-pure CsCu₂I₃ nanorods were steadily obtained at 180 °C. Structural evolution from less copper-containing NCs to copper-rich ones in the low-temperature reaction condition is highly related to the coordination of copper ions with OAm. More importantly, accompanying the growth of nanorods and structural evolution from Cu₃Cs₂I₅ to CsCu₂I₃, the color of photoluminescence emission of NCs changed from blue to nearly white and to yellow, but their photoluminescence quantum yield decreased from 36.00 to 9.86%. The finding in this work would give a view to the structural evolution of copper-containing perovskite-like halides, being helpful for adjusting their photoluminescence in white LEDs.

An ultraviolet excitation anti-counterfeiting material of Sb3+ doped Cs2ZrCl6 vacancy-ordered double perovskite

Application of Sb3+ doped Cs2ZrCl6 vacant-ordered double perovskite in anti-counterfeiting. The blue and orange emissions come from the self-trapped exciton emission of the Cs2ZrCl6 matrix and the ion transitions of Sb3+, respectively.

Recent progress of zero-dimensional luminescent metal halides

This review provides in-depth insight into the structure–luminescence–application relationship of 0D all-inorganic/organic–inorganic hybrid metal halide luminescent materials.

All-inorganic lead-free metal halide perovskite quantum dots: progress and prospects

Lead halide perovskite quantum dots have drawn worldwide attention due to their quantum confinement effect and excellent optical gain properties. It is worth noting that due to the toxicity of lead ions and the inherent instability of organic groups, research on all-inorganic lead-free metal halide perovskite quantum dots (ILFHPQDs) has become a hot spot in recent years. This paper summarizes the latest research progress of ILFHPQDs, analyzes the sources and limitations affecting the performance of ILFHPQDs, and provides the improvement methods. Firstly, the typical synthesis strategies of ILFHPQDs are discussed, followed by a focus on the structural characteristics, optoelectronic properties and stability of each type of ILFHPQD. Next, the applications of ILFHPQDs in devices are investigated. Finally, the challenges, solutions and future application directions of ILFHPQDs are prospected.

Efficient Lone-Pair-Driven Luminescence: Structure-Property Relationships in Emissive 5s2 Metal Halides

Low-dimensional metal halides have been the focus of intense investigations in recent years following the success of hybrid lead halide perovskites as optoelectronic materials. In particular, the light emission of low-dimensional halides based on the 5s2 cations Sn2+ and Sb3+ has found utility in a variety of applications complementary to those of the three-dimensional halide perovskites because of its unusual properties such as broadband character and highly temperature-dependent lifetime. These properties derive from the exceptional chemistry of the 5s2 lone pair, but the terminology and explanations given for such emission vary widely, hampering efforts to build a cohesive understanding of these materials that would lead to the development of efficient optoelectronic devices. In this Perspective, we provide a structural overview of these materials with a focus on the dynamics driven by the stereoactivity of the 5s2 lone pair to identify the structural features that enable strong emission. We unite the different theoretical models that have been able to explain the success of these bright 5s2 emission centers into a cohesive framework, which is then applied to the array of compounds recently developed by our group and other researchers, demonstrating its utility and generating a holistic picture of the field from the point of view of a materials chemist. We highlight those state-of-the-art materials and applications that demonstrate the unique capabilities of these versatile emissive centers and identify promising future directions in the field of low-dimensional 5s2 metal halides.

Luminescence in Manganese (II)-Doped SrZn2S2O Crystals From Multiple Energy Conversion

Under the excitation of ultraviolet, X-ray, and mechanical stress, intense orange luminescence (Mn2+, 4T1 → 6A1) can be generated in Mn2+-doped SrZn2S2O crystal in orthorhombic space group of Pmn21. Herein, the multiple energy conversion in SrZn2S2O:Mn2+, that is, photoluminescence (PL), X-ray-induced luminescence, and mechanoluminescence, is investigated. Insight in luminescence mechanisms is gained by evaluating the Mn2+ concentration effects. Under the excitation of metal-to-ligand charge-transfer transition, the most intense PL is obtained. X-ray-induced luminescence shows similar features with PL excited by band edge UV absorption due to the same valence band to conduction band transition nature. Benefiting much from trap levels introduced by Mn2+ impurities, the quenching behavior mechanoluminescence is more like the directly excited PL from Mn2+ d-d transitions. Interestingly, this concentration preference leads to varying degrees of spectral redshift in each mode luminescence. Further, SrZn2S2O:Mn2+ exhibits a good linear response to the excitation power, which makes it potential candidates for applications in X-ray radiation detection and mechanical stress sensing.

Highly efficient eco-friendly X-ray scintillators based on an organic manganese halide

Scintillation based X-ray detection has received great attention for its application in a wide range of areas from security to healthcare. Here, we report highly efficient X-ray scintillators with state-of-the-art performance based on an organic metal halide, ethylenebis-triphenylphosphonium manganese (II) bromide ((C38H34P2)MnBr4), which can be prepared using a facile solution growth method at room temperature to form inch sized single crystals. This zero-dimensional organic metal halide hybrid exhibits green emission peaked at 517 nm with a photoluminescence quantum efficiency of ~ 95%. Its X-ray scintillation properties are characterized with an excellent linear response to X-ray dose rate, a high light yield of ~ 80,000 photon MeV-1, and a low detection limit of 72.8 nGy s-1. X-ray imaging tests show that scintillators based on (C38H34P2)MnBr4 powders provide an excellent visualization tool for X-ray radiography, and high resolution flexible scintillators can be fabricated by blending (C38H34P2)MnBr4 powders with polydimethylsiloxane.

Air-Stable Bulk Halide Single-Crystal Scintillator Cs3Cu2I5 by Melt Growth: Intrinsic and Tl Doped with High Light Yield

Ternary metal halides with large exciton binding energy have recently gained considerable attention in the optoelectronic field due to their high photoluminescence quantum yield and large Stokes shift. Here, efficient scintillators are designed based on these advantageous properties. For the first time, bulk Cs₃Cu₂I₅ is grown using a melt method other than the intensively reported solution growth, and behaved as an intrinsic scintillator, emitting bright blue (∼450 nm) light under X-ray and γ-ray irradiation. Successful Tl doping at Cs sites tune the emission band over the entire visible range (400-700 nm) due to the synergetic effects of self-trapped excitons (STEs) and Tl centers. Notably, after doping with 1% Tl⁺, the scintillation light yield of Cs₃Cu₂I₅ increases by nearly three times to 51 000 ± 2000 ph/MeV (Cs-137, 662 keV). Cs₃Cu₂I₅:Tl shows a higher energy resolution of 4.5% at 662 keV than that of NaI:Tl and an excellent nonproportionality (<3%) in the γ-ray energy range of 60-1275 keV. A model of energy relaxation in Cs₃Cu₂I₅:Tl scintillators is proposed and discussed. In particular, it is the first Cu-based halide scintillator that has air stability, good stopping power, and the ability to grow large bulk single crystals for practical application. This work provides a strategy for tuning and broadening the spectral range of STE emitters, and bridges the lead-free halide derivatives with scintillators.

All-inorganic copper(i)-based ternary metal halides: promising materials toward optoelectronics

All-inorganic lead halides, including CsPbX₃ (X = Cl, Br, I), have become important candidate materials in the field of optoelectronics. However, the inherent toxicity of metal lead and poor material stability have hindered further applications of traditional metal halides, CsPbX₃. Therefore, copper(i)-based ternary metal halides are expected to become promising substitutes for traditional metal halides because of their nontoxicity, excellent optical properties and good stability under ambient conditions. This article reviews the recent development of all-inorganic low-dimensional copper(i)-based ternary metal halides by introducing their various synthesis methods, crystal structures, properties and their optoelectronic applications. In addition, the prospects for future challenges and the potential significance of copper(i)-based ternary metal halides in optoelectronic fields are presented.

Bright Blue Emitting Cu-Doped Cs2ZnCl4 Colloidal Nanocrystals

We report here the synthesis of undoped and Cu-doped Cs₂ZnCl₄ nanocrystals (NCs) in which we could tune the concentration of Cu from 0.7 to 7.5%. Cs₂ZnCl₄ has a wide band gap (4.8 eV), and its crystal structure is composed of isolated ZnCl₄ tetrahedra surrounded by Cs⁺ cations. According to our electron paramagnetic resonance analysis, in 0.7 and 2.1% Cu-doped NCs the Cu ions were present in the +1 oxidation state only, while in NCs at higher Cu concentrations we could detect Cu(II) ions (isovalently substituting the Zn(II) ions). The undoped Cs₂ZnCl₄ NCs were non emissive, while the Cu-doped samples had a bright intragap photoluminescence (PL) at ∼2.6 eV mediated by band-edge absorption. Interestingly, the PL quantum yield was maximum (∼55%) for the samples with a low Cu concentration ([Cu] ≤ 2.1%), and it systematically decreased when further increasing the concentration of Cu, reaching 15% for the NCs with the highest doping level ([Cu] = 7.5%). The same (∼2.55 eV) emission band was detected under X-ray excitation. Our density functional theory calculations indicated that the PL emission could be ascribed only to Cu(I) ions: these ions promote the formation of trapped excitons, through which an efficient emission takes place. Overall, these Cu-doped Cs₂ZnCl₄ NCs, with their high photo- and radio-luminescence emission in the blue spectral region that is free from reabsorption, are particularly suitable for applications in ionizing radiation detection.