Ligand-Induced Tunable Dual-Color Emission Based on Lead Halide Perovskites for White Light-Emitting Diodes

Zinc-halide/phenylbutyrate co-passivation of CsPbX3 nanocrystals toward efficient and robust luminescence

Cesium lead halide perovskite nanocrystals (IPNCs) exhibit excellent optoelectronic properties but are susceptible to degradation in practical environments due to their ionic surface and unstable ligand capping. Here, we propose a post-synthesis surface passivation strategy for CsPbX3 (X = Br, I) IPNCs by employing combined zinc halide and zinc phenylbutyrate (Zn(PA)2) as surface ligands. ZnBr2 fills surface halide vacancies on IPNCs, resulting in high photoluminescence efficiency, whereas Zn(PA)2 stabilizes IPNCs by substituting surface ammonium ligands. Additionally, the -PA capping endows IPNCs with high solubility in polystyrene (PS), enabling the direct fabrication of highly efficient and uniform IPNCs-PS color conversion films through in situ polymerization of the IPNC-styrene solution. The resulting IPNCs-PS films displayed significantly enhanced stability, retaining excellent PL persistence after 1000 h of photoaging. This novel ligand and modification method presents a promising strategy for improving the efficiency and stability of IPNCs, facilitating their potential applications in display backlight and other optoelectronic applications.

Excitation-Power-Dependent Color Tuning in a Single Sn-Doped CdS Nanowire

Multicolor emission and dynamic color tuning with large spectral range are challenging to realize but critically important in many areas of technology and daily life, such as general lighting, display, multicolor detection and multi-band communication. Herein, we report an excitation-power-dependent color-tuning emission from an individual Sn-doped CdS nanowire with a large spectral range and continuous color tuning. Its photoluminescence (PL) spectrum shows a broad trap-state emission band out of Sn dopants, which is superposed by whispering-gallery (WG) microcavity due to the nanostructure size and its structure, besides the CdS band-edge emission. By simply changing the excitation power from 0.25 to 1.36 mW, we demonstrate that the typical Sn-doped CdS nanowire with the weight ratio of 10:1 of CdS and SnO2, the emission color can change from red to orange to yellow to green. In view of the stable properties and large spectral range, the Sn-doped CdS nanowires are very promising potential candidates in nanoscale optoelectronic devices.

Stability Enhancement in All-Inorganic Perovskite Light Emitting Diodes via Dual Encapsulation

Addressing the challenge of lighting stability in perovskite white light emitting diodes (WLEDs) is crucial for their commercial viability. CsPbX3 (X = Cl, Br, I, or mixed) nanocrystals (NCs) are promising for next-generation lighting due to their superior optical and electronic properties. However, the inherent soft material structure of CsPbX3 NCs is particularly susceptible to the elevated temperatures associated with prolonged WLED operation. Additionally, these NCs face stability challenges in high humidity environments, leading to reduced lighting performance. This study introduces a two-step dual encapsulation method, resulting in CsPbBr3@SiO2/Al2SiO5 composite fibers (CFs) with enhanced optical stability under extreme conditions. In testing, WLEDs incorporating these CFs, even under prolonged operation at high power (100 mA for 9 h), maintain consistent electroluminescence (EL) intensity and optoelectronic parameters, with surface temperatures reaching 84.2 °C. Crucially, when subjected to 85 °C and 85% relative humidity for 200 h, the WLEDs preserve 97% of their initial fluorescence efficiency. These findings underscore the efficacy of the dual encapsulation strategy in significantly improving perovskite material stability, marking a significant step toward their commercial application in optoelectronic lighting.

Cyanuric Acid-Functionalized Perovskite Nanocrystals toward Low Interface Impedance, High Environmental Stability, and Superior Electrochemiluminescence

Perovskite nanocrystals (PNs) have received much attention as luminescence materials in the field of electrochemiluminescence (ECL). However, as one key factor for determining the optoelectronic properties of the surface state of PNs, the surface passivation layer of PNs has enormous difficulty in simultaneously meeting the requirements of high ECL efficiency, conductivity, and stability. Herein, an effective surface modification strategy with cyanuric acid (CA) is used to solve such issue. As confirmed, the CA molecules are chemically anchored onto the surface of PNs via the Lewis interaction between π electrons of the triazine ring and the empty orbit of Pb2+. Benefiting from the above interaction, the electrochemical impedance of PNs is decreased greatly without the loss of light-emitting efficiency. Moreover, the stability of PNs under O2 exposure is improved by almost sixfold. These improvements are confirmed to be beneficial for enhancing the ECL behaviors of PNs under electrochemical operation. Upon cathode ECL driving conditions in aqueous media, the ECL intensity and efficiency of PNs are increased to 200 and 170%, respectively. This work provides a new modification strategy to holistically improve the ECL performance of PNs, which is instructive to exploring robust perovskite nanomaterials for electrochemical applications.

Single-phase white light material and antibiotic detection of lanthanide metal-organic frameworks

WLEDs have been widely used in lighting and display equipment due to their energy-saving and environment-friendly advantages, but it is still a great challenge to construct high-quality single-phase white light materials for the preparation of WLEDs. In this work, three Ln-MOFs (HNU-82-84) with the same structure were synthesized by assembling rare earth ions (Tb3+, Eu3+, La3+) and 4,4',4''-nitrilotribenzoic acid (H3TCA) ligands. The structure and optical properties of the three compounds were investigated. Under the ultraviolet lamp, HNU-82-84 displays green light, red light, and blue light emission, respectively. Based on the RGB principle, aiming at the single-phase white material, the proportion of adding rare earth ions is reasonably adjusted to design and synthesize the Ln-MOF (Eu0.015Tb0.037La0.148-TCA) with CIE chromaticity coordinates of (0.319, 0.344). In addition, the WLED was prepared by Eu0.015Tb0.037La0.148-TCA and commercial LED lamps. Furthermore, HNU-82 has strong fluorescence emission and good water stability and can be used to detect nitrofurazone (NZF) and nitrofurantoin (NFT). The concentrations of the aqueous solutions of NZF and NFT had a well correlated linear relationship with the fluorescence quenching effect of HNU-82, and the detection limits were 6.60 × 10-7 mol L-1 and 4.62 × 10-7 mol L-1, respectively. Hence, HNU-82 also has potential as a fluorescent sensor for the detection of NZF and NFT in the aquatic environment.

In situ synthesis of high-quantum-efficiency and stable bromide-based blue-emitting perovskite nanoplatelets

We present a facile synthetic approach for the growth of two-dimensional CsPbBr₃ nanoplatelets (NPLs) in the temperature range of 50-80 °C via the vacuum-assisted low-temperature (VALT) method. In this method, we utilized the solubility of the PbBr₂ precursor at temperatures high than the reaction temperature, thus making Br available during the reaction to form NPLs with fewer defects. The high chemical availability of Br during the reaction changes the growth dynamics and formation of highly crystalline nanoplatelets. Using this method, we have synthesized NPLs with an emission wavelength range of 450 to 485 nm that have high photoluminescence quantum yields (PLQY) from 80 to 100%. The synthesized NPLs retain their initial PLQY of about 80% after one month at ambient conditions. The formation of NPLs with fewer defects and enhanced radiative recombination was further confirmed by X-ray diffraction (XRD), reduced Urbach energy, time-resolved photocurrent measurements, X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared (FTIR) spectroscopy. Additionally, we utilized the synthesized NPLs for the fabrication of down-conversion light emitting diodes (LEDs), and the electroluminescence peak was barely shifted compared to the photoluminescence peak.

CsPbBr3 perovskite nanoplatelets: Excellent probes for spectrofluorimetric sensing of chloride and arsenite

Herein, we report a novel analytical exploitation of selective but very facile anion exchange induced phase transformations of CsPbBr₃ Perovskite crystallites. Specifically, with CsPbBr₃ Perovskite as Spectrofluorimetric probes, we demonstrate a simple, quick and economical analytical procedure for sensing and quantification of chloride content in room temperature ionic liquids (RTILs), and that of toxic pollutant Arsenic (III) in water samples. The presented approach relies on the variations in photoluminescence characteristics of CsPbBr₃ Perovskite nanoplatelets on account of very facile substitution of their bromide ions by chloride ions available in their vicinity. This unique property of CsPbBr₃ Perovskite nanoplatelets ensures detection of chloride impurity in RTIL samples, within the concentration range of 0.007-0.016 ppb with LOD c.a. 0.0010 ppb ± 0.44% and of Arsenic in water samples within the concentration range 0.48-4.32 ppb with LOD as low as c.a. 0.074 ppb ± 0.46%.

Tunable Dual-Color Emission Perovskites via Post-Synthetic Modification Strategy for Near-Unity Photoluminescence Quantum Yield

Lead halide perovskites (LHPs) with excellent performance have become promising materials for optoelectrical devices. However, as for the dual-color emission LHPs (DELHPs), the low photoluminescence quantum yield (PLQY) hinders their applications. Herein, a simple low-cost room-temperature post-synthetic modification strategy is used to achieve a near-unity PLQY of DELHPs. It is proven that ZnBr₂ plays an important role as an inorganic ligand in reducing surface defects to induce a 95.4% increase in the radiative decay rate and a 99.5% decrease in the nonradiative decay rate in the treated DELHPs compared with the pristine DELHPs. The performance of the blue emission from the surface lattice is greatly improved via the modification of ZnBr₂. DELHPs with different ratios of blue and green emissions are obtained by changing the specific surface area and ZnBr₂ concentration. The distribution and mechanism of Zn²⁺ are discussed using the research model based on these DELHPs. The first example of the single-layer dual-color perovskite electroluminescence device is realized from DELHPs. This work provides a new perspective for improving the performance of DELHPs, which will greatly accelerate the development of emission materials of LHPs.

Emergence of Impurity-Doped Nanocrystal Light-Emitting Diodes

In recent years, impurity-doped nanocrystal light-emitting diodes (LEDs) have aroused both academic and industrial interest since they are highly promising to satisfy the increasing demand of display, lighting, and signaling technologies. Compared with undoped counterparts, impurity-doped nanocrystal LEDs have been demonstrated to possess many extraordinary characteristics including enhanced efficiency, increased luminance, reduced voltage, and prolonged stability. In this review, recent state-of-the-art concepts to achieve high-performance impurity-doped nanocrystal LEDs are summarized. Firstly, the fundamental concepts of impurity-doped nanocrystal LEDs are presented. Then, the strategies to enhance the performance of impurity-doped nanocrystal LEDs via both material design and device engineering are introduced. In particular, the emergence of three types of impurity-doped nanocrystal LEDs is comprehensively highlighted, namely impurity-doped colloidal quantum dot LEDs, impurity-doped perovskite LEDs, and impurity-doped colloidal quantum well LEDs. At last, the challenges and the opportunities to further improve the performance of impurity-doped nanocrystal LEDs are described.

Stable green and red dual-color emission in all-inorganic halide-mixed perovskite single microsheets

Recently, all-inorganic perovskites have attracted tremendous attention due to their excellent optoelectronic properties and extensive potential applications. However, these perovskites usually show a single emission wavelength because of the high ionic migration. Herein, we synthesized all-inorganic halide-mixed perovskite CsPbBr x I3-x microsheets with high crystal quality using the anti-solvent solution method and observed extraordinary green and red dual-color emission in single CsPbBr x I3-x microsheets. Power dependent PL spectra reveal excitonic and defect related recombination features of CsPbBr3 and CsPbI3 for the green and red emission. Temperature dependent PL spectra indicated a distinctive exciton-phonon coupling strength in CsPbBr x I3-x microsheets compared with pure CsPbBr3 and CsPbI3. The PL dynamics showing longer emission lifetime further confirmed this conclusion. Our work not only provides a novel strategy to produce stable dual-color emission integration, but also promotes the fundamental insight into the emission dynamics and exciton/free carrier related photophysics in all-inorganic halide-mixed perovskites.

Synthesis of Colloidal Blue-Emitting InP/ZnS Core/Shell Quantum Dots with the Assistance of Copper Cations

Colloidal InP quantum dots (QDs) have been considered as one of the most promising candidates for display and biolabeling applications because they are intrinsically toxicity-free and exhibit high photoluminescence. On account of the uncontrollable nucleation and growth during the synthesis of InP, obtaining high-quality blue-emitting InP QDs with uniform size distribution remains a challenge. Herein, we employ a novel synthetic approach for producing blue-emitting InP/ZnS core/shell QDs with the assistance of copper cations. The studies reveal that the copper ions could combine with phosphorus precursor to form hexagonal Cu_3-xP nanocrystals, which competed with the nucleation process of InP QDs, resulting in the smaller sized InP QDs with blue photoluminescence emission. After the passivation of InP QDs with the ZnS shell, the synthesized InP/ZnS core/shell QDs present bright blue emission (∼425 nm) with a photoluminescence quantum yield of ∼25%, which is the shortest wavelength emission for InP QDs to date. This research provides a new way to synthesize ultrasmall semiconductor nanocrystals.