Phase-Selective Solution Synthesis of Cd-Based Perovskite Derivatives and Their Structure/Emission Modulation

Multifunctional Phosphor with High-Efficient Near-Infrared Emission Based on Antimony-Zinc Halides

Metal halide-based broadband near-infrared (NIR) luminescent materials face problems such as complicated preparation, high cost, low photoluminescence quantum yield, and high excitation energy. Here, incorporating Sb3+ and Br- into (C20H20P)2ZnCl4 crystals allowed for the achievement of efficient broadband near-infrared emission under 400 nm excitation while maintaining satisfactory environmental and thermal stability. The compounds exhibit a broad range of emission bands from 550 to 1050 nm, with a photoluminescence quantum yield of 93.57%. This is a groundbreaking achievement for organic-inorganic hybrid metal halide NIR luminescent materials. The near-infrared emission is suggested to originate from [SbX5]2-, as supported by the femtosecond transient absorption spectra and density-functional theory calculations. This phosphor-based NIR LEDs successfully demonstrate potential applications in night vision, medical imaging, information encryption, and anticounterfeiting.

Multisite Fine-Tuning in Hybrid Cadmium Halides Enables Wide Range Emissions for Anti-Counterfeiting

Achieving tunable emissions spanning the spectrum, from blue to near-infrared (NIR) light, within a single component is a formidable challenge with significant implication, particularly in tailoring multicolor luminescence for anti-counterfeiting purposes. In this study, we demonstrate a broad spectrum of emissions, covering blue to red and extending into NIR light in [BPy]2CdX4 : xSb3+ (BPy=Butylpyridinium; X=Cl, Br; x=0 to 0.08) through precise multisite structural fine-tuning. Notably, the multicolor emissions from [BPy]2CdBr4 : Sb3+ manifest a distinctive pattern, transitioning from blue to yellow in tandem with the host [BPy]2CdBr4 and further extending from yellow to NIR with its homologous [BPy]2CdCl4 : Sb3+, resulting in the simultaneous presence of intersecting and independent emission colors. Detailed modulation of chemical composition enables partial luminescence switching, facilitating the creation of diverse patterns with multicolor luminescence by employing [BPy]2CdX4 : xSb3+ as phosphors. This study for the first time successfully implements several groups of tunable emission colors in a single matrix via multisite fine-tuning. Such an effective strategy not only develops the specific relationships between tunable emissions and adjustable compositions, but also introduces a cost-effective and straightforward approach to achieving unique, high-level, plentiful-color and multiple-information-storage labels for advanced anti-counterfeiting applications.

Excited State Regulated Emission in Hybrid Indium Halides via Crystal Structure Switch

Organic-inorganic metal halides have become one of the most promising materials in the next generation of optoelectronic applications due to their high charge carrier mobility and tunable band gaps. In this study, Sb:PA6InCl9 and Sb:PA4NaInCl8 single crystals were prepared through evaporation crystallization, respectively. Due to the different degrees of lattice distortions, the highly efficient yellow emission in Sb:PA6InCl9 at 610 nm and the green emission in Sb:PA4NaInCl8 at 545 nm were achieved by regulation of the excited state, respectively. By introducing additional sodium ions in the post-treatment, we found that the zero-dimensional Sb:PA6InCl9 could rapidly convert into a two-dimensional layered structure of Sb:PA4NaInCl8, thus resulting in a novel green/yellow emission switch. This work guides the structural and performance control of organic-inorganic hybrid In-based metal halides and offers broad prospects for luminescent switching in anticounterfeiting applications.

Sb3+-Doped Indium-Based Metal Halide (Gua)3InCl6 with Efficient Yellow Emission

In recent years, low-dimensional organic-inorganic hybrid metal halides (OIHMHs) have shown excellent photophysical properties due to their quantum structure, adjustable energy levels, and energy transfer between inorganic and organic components, which have attracted extensive attention from researchers. Herein, we synthesize a zero-dimensional (0D) OIHMH, Sb3+:(Gua)3InCl6, by introducing Sb3+ into (Gua)3InCl6, which undergoes a significant enhancement of the emission peak at 580 nm with the photoluminescence quantum yield (PLQY) boosted from 17.86 to 95.72% when excited at 340 nm. This boost in photoluminescence of the doped sample was studied by combining ultrafast femtosecond transient absorption, temperature-dependent photoluminescence (PL) spectra, and density functional theory (DFT) calculation, revealing the process of self-trapped exciton (STE) recombination to emit light at both Sb and In sites in this 0D structure simultaneously. This material with the lowest dark STE level at the In site for emission in the undoped sample can amazingly yield very strong emission in the doped sample, which has never been observed before. Finally, we tested its application in a photoelectric device. This work not only helps to gain a deeper understanding of the formation of STEs in In-based halides but also plays a certain guiding role in the design of new luminescent materials.

Enhanced Photoluminescence Quantum Yield of Metal Halide Perovskite Microcrystals for Multiple Optoelectronic Applications

Recently, metal 1halide perovskites have shown compelling optoelectronic properties for both light-emitting devices and scintillation of ionizing radiation. However, conventional lead-based metal halide perovskites are still suffering from poor material stability and relatively low X-ray light yield. This work reports cadmium-based all-inorganic metal halides and systematically investigates the influence of the metal ion incorporation on the optoelectronic properties. This work introduces the bi-metal ion incorporation strategy and successfully enhances the photoluminescence quantum yield (98.9%), improves thermal stability, and extends the photoluminescence spectra, which show great potential for white light emission. In addition, the photoluminescent decay is also modulated with single metal ion incorporation, the charge carrier lifetime is successfully reduced to less than 1 µs, and the high luminescent efficiency and X-ray light yield (41 000 photons MeV-1 ) are maintained. Then, these fast scintillators are demonstrated for high-speed light communication and sensitive X-ray detection and imaging.

Luminescent Behavior of Sb3+-Activated Luminescent Metal Halide

Metal halide perovskites have unparalleled optoelectronic properties and broad application potential and are expected to become the next epoch-making optoelectronic semiconductors. Although remarkable achievements have been achieved with lead halide perovskites, the toxicity of lead inhibits the development of such materials. Recently, Sb3+-activated luminescent metal halide perovskite materials with low toxicity, high efficiency, broadband, large Stokes shift, and emission wavelengths covering the entire visible and near-infrared regions have been considered one of the most likely luminescent materials to replace lead halide perovskites. This review reviews the synthesis, luminescence mechanism, structure, and luminescence properties of the compounds. The basic luminescence properties of Sb3+-activated luminescent metal halide perovskites and their applications in WLED, electroluminescence LED, temperature sensing, optical anti-counterfeiting, and X-ray scintillators are introduced. Finally, the development prospects and challenges of Sb3+-activated luminescent metal halide perovskites are discussed.

Enhancing Luminescence in Hue-Tunable White-Light Emitting K4CdCl6:Sb3+,Mn2+ All-Inorganic Halide Perovskites: Insights from Defect Engineering and Energy Transfer

All-inorganic halide perovskites (AIHPs) have emerged as highly promising optoelectronic materials owing to their remarkable properties, such as high-optical absorption coefficients, photoluminescence efficiencies, and dopant tolerance. Here, we investigate the AIHPs K4CdCl6:Sb3+,Mn2+ that demonstrate hue-tunable white-light emission with an exceptional photoluminescence quantum yield of up to 97%. Through a detailed investigation, we reveal that efficient energy transfer from Sb3+ to Mn2+ plays a dominant role in the photoluminescence of Mn2+, instead of the conventional 4T1g → 6A1g transition of Mn2+. Thermodynamic analysis highlights the crucial role of a Cl-rich environment in obtaining the K4CdCl6 phase, while transformation from K4CdCl6 to KCdCl3 can be achieved under Cl-poor and K-poor conditions. The theoretical analysis reveals that defect Cli is more readily formed compared to defect VK, corroborating experimental findings that the K4CdCl6:Sb3+ phase is exclusively obtained when the solution contains HCl concentrations higher than 4 mol L-1. Our work provides valuable insights into the photoluminescence mechanism of Sb3+, defect engineering through heterovalent doping, and efficient energy transfer between Sb3+ and Mn2+ in K-Cd-Cl-based perovskites, which offers a new perspective for the design and development of novel AIHPs with superior optoelectronic performance.

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.

Green Triplet Self-Trapped Exciton Emission in Layered Rb3Cd2Cl7:Sb3+ Perovskite: Comparison with RbCdCl3:Sb3

Metal halide materials have recently sparked intense research because of their excellent photophysical properties and chemical stability. For example, RbCdCl₃:Sb³⁺ exhibits broad emission at about 600 nm with a high photoluminescence quantum yield (PLQY) over 91% and double emission bands with bright white color. Herein, we obtained a novel Rb and Cd layered perovskite Rb₃Cd₂Cl₇ doped with Sb³⁺, which gives luminescence at 525 nm with a large Stokes shift of 200 nm, originating from a self-trapped exciton (STE). Its PLQY is 57.47%, but its low-temperature PLQY becomes much higher at the same wavelength. When Rb₃Cd₂Cl₇:Sb³⁺ and RbCdCl₃:Sb³⁺ were compared, the two classes of quantum confinement effects by Rb and Cd ions in the lattice were identified to describe their electronic states and different optical properties. These results suggest that properties of Sb-doped cadmium halides could be modified by the structure type and local atomic confinement to find applications as promising luminescent materials for optoelectronic devices.

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.

H2O-NH4+-Induced Emission Modulation in Sb3+-Doped (NH4)2InCl5·H2O

Lead-based metal halide perovskites have received widespread attention for their promising application prospects in the field of lighting and display due to their excellent optical properties. However, the toxicity of lead may hinder their further commercial application. Herein, a zero-dimensional (0D) metal halide (NH₄)₂InCl₅·H₂O with an orthorhombic structure and the Pnma space group was produced. With doping with Sb³⁺, these products exhibit one highly efficient and wide yellow emission band (∼450-850 nm) in their photoluminescence (PL) spectra, which covers almost the entire visible spectral range at room temperature; however, they give two emission bands with long decay lifetimes (microseconds) at low temperature. Temperature-dependent steady-state PL, transient PL spectroscopy, temperature-dependent Raman spectra characterization, and theoretical band structure calculations confirm that the dual-band emission at low temperature originates from the dual vibronic levels of the self-trapped exciton (STE) in the hole-vibration state, whose vibration energy is related to the H₂O-NH₄⁺ connection in the valence band. This result proves that the vibronic state in STE formation involves both electrons and holes in the excited states, the opposite of this happens in the electron-vibration band in most perovskite halides. These results provide new insight into the luminescent mechanism of Sb³⁺ in halide perovskites, especially used for emission color modulation by the temperature-dependent electron- or hole-vibration processes.