Stable Photoluminescence Research Articles

Optical time-lapsed in situ mechanochemical studies on metal halide perovskite systems.

Metal halide perovskites are attractive for optoelectronic applications, but the existing solution-based synthetic methods rely on hazardous solvents and lack reproducibility. To overcome these challenges, solvent-free mechanochemical synthesis of perovskites can be conducted, although traditional opaque ball milling equipment hinder real-time monitoring of the reaction progress. Herein, mechanochemistry was performed with time-lapsed in situ (TLIS) measurements to elucidate the optical properties during the synthesis. The TLIS spectrometer enabled real-time observation of the impact of varying the compositions on the absorption properties of formamidinium/methylammonium lead iodide (FAxMA1-xPbI3, x = 0 to 1) and facilitated optimization of the synthesis duration. Moreover, we can accelerate the evaluation and directly observe the effects of different synthetic strategies for enhancing the photoluminescence quantum yield and stability of the perovskites, providing near-infrared (NIR) emitting tin-based perovskites FASnIzBr3-z (where z = 0 to 3) with core-shell structures. Intriguingly, halide ion migration was deduced in lead-free double perovskites Cs2NayAg1-yBiCl6 (y = 0 to 1.0) at room temperature during aging after mechanochemical activation. Our work provides insights into the mechanochemistry of compounds with low thermodynamic barriers.

Quantum Dot Luminescence Microspheres Enable Ultra-Efficient and Bright Micro-LEDs.

Quantum dot (QD)-converted micrometer-scale light-emitting diodes (micro-LEDs) are regarded as an effective solution for achieving high-performance full-color micro-LED displays because of their narrow-band emission, simplified mass transfer, facile drive circuits, and low cost. However, these micro-LEDs suffer from significant blue light leakage and unsatisfactory electroluminescence properties due to the poor light conversion efficiency and stability of the QDs. Herein, the construction of green and red QD luminescence microspheres with the simultaneously high conversion efficiency of blue light and strong photoluminescence stability are proposed. These luminescence microspheres exhibit high external photoluminescence quantum yields exceeding 46% under 450nm excitation, along with excellent reliability against blue light, heat, and water-oxygen degradation, owing to the waveguide and spatial confinement effects of the microspheres. The microsphere-based green and red micro-LEDs achieve world-record external quantum efficiencies of 40.8% and 22.1%, respectively, and high brightness values of 1.7×108 and 7.6×107cdm-2, respectively. Finally, 0.6inch red, green, and blue monochrome micro-LED displays are demonstrated by integrating microsphere-converted micro-LED arrays with thin-film transistor backplanes, which show a pixel resolution as high as 1700 PPI and brightness exceeding 10000cdm-2.

N-Alkyl Chain Induced Molecular Aggregation in Mononuclear Gold(I)-N-Heterocyclic Carbene Complexes for Blue Light Emitting Applications.

The gold(I) N-heterocyclic carbene (NHC) molecule exhibits outstanding luminescent properties along with high thermal stability due to its strong carbene gold bond. Gold(I)-NHC complexes are known to emit green to yellow color, while blue emission is limited. Herewith, we report the photoluminescence and thermal stability correlation between blue emitting mononuclear gold(I)-NHC chloride complexes, N-(9-anthracenyl)-N'(n-alkyl)imidazol-2-ylidene gold(I) chloride (alkyl=n-butyl (1), n-pentyl (2), n-hexyl (3)). These complexes were synthesized by transmetallation route and characterized by FT-IR, NMR, TGA, and single crystal X-ray diffraction analysis. The solid-state study reveals a unique molecular packing due to hydrogen bonding, aurophilic interaction, and CH⋅⋅⋅π interactions in all 1-3. In addition, the π⋅⋅⋅π stacking has been found in 1. All these complexes show good thermal stability due to the strong metal-ligand bond strength along with crystal packing. In addition, 1-3 emits a blue colour in both solution and crystalline state. The quantum yield in the crystalline state was found to be higher for 1 (22.44 %) compared to 2 (9.90 %), and 3 (14.98 %). A similar high quantum yield for blue-emitting gold(I)-NHC chloride complex is rare. This promising quantum yield for 1 can be ascribed to the crystal packing effect. The theoretical calculations were carried out to understand the electronic and structural properties of 1-3. Computational studies revealed the origin of the luminescence behaviour of complexes. The blue light emitting thin film and LED are demonstrated using 1 exhibited the emission peak at the blue region with Commission Internationale de L'Eclairage (CIE) coordinates near the National Television Standards Committee (NTSC) value.

Highly Fluorescent Bio-Synthesized Carbon Quantum Dots for Latent Fingerprint Detection.

This study introduces an innovative approach to high-resolution latent fingerprint detection using carbon quantum dots (CQDs) biosynthesized from spent coffee grounds, enhanced with nitrogen doping. Conventional fingerprinting methods frequently use hazardous chemicals and are costly, highlighting the need for eco-friendly, affordable alternatives that preserve detection quality. The biosynthesized nitrogen-doped CQDs exhibit strong photoluminescence and high stability, offering a sustainable, effective alternative for fingerprint imaging. Using a one-step hydrothermal synthesis method, nitrogen-doped CQDs were developed, displaying intense cyan fluorescence under UV light at 365nm. The quantum yield was measured to be 19.73%. Characterization through UV-Visible and photoluminescence spectroscopy, FTIR, XRD and TEM confirmed the morphology, surface properties, optical properties and stability. The average particle size diameter was calculated to be around 8.71 ± 0.14nm. These CQDs were tested on various non-porous surfaces including marble, glass, aluminium, and metal where they provided detailed visualization of fingerprint ridge patterns, sweat pores, and minutiae with high fluorescence. Notably, the CQDs demonstrated excellent adherence and sustained fluorescence, maintaining photostability for up to 60 days under dark storage conditions at 2-8°C. This sustainable synthesis method thus produces nitrogen-doped CQDs with robust fluorescent properties, establishing a promising, eco-friendly solution for high-resolution latent fingerprint detection in forensic investigations.

Elevating Red Emission: Yb3+ Doped CsPbBr1I2 Nanocrystal Glass for Exceptional PLQY and Stability in Wide Color Gamut Backlit Displays

As display technologies progress towards enhanced visual performance, there was a growing demand for color conversion materials to meet increasingly stringent performance requirements. In recent years, all-inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) had gained attention in the field of wide color gamut backlight displays due to their tunable full spectrum, narrow-band emission, high color purity, and ease of processing. However, red-emitting perovskite NCs were still facing challenges with photoluminescence quantum yield (PLQY) and stability. In this study, Yb3+ doped CsPbBr1I2 perovskite nanocrystal glass (Yb3+@CsPbBr1I2 PNG) was synthesized using a melt-quenching technique. Samples emitting at a narrow band centered at 630nm, with a full width at half maximum(FWHM) of 31.8nm, exhibited a high PLQY of 80.36% and retained fluorescence intensity at 98.2% of the initial value in water, maintaining to 92.6% after continuous blue light irradiation for 60 days. Moreover, the optical conversion film Yb3+@CsPbBr1I2@CsPbBr3@PET developed in our study showcased color gamut coverage surpassing 132.9% of the NTSC 1953 standard and 98.8% of the Rec.2020 standard. In summary, the highly efficient and remarkably stable red-emitting Yb3+@CsPbBr1I2 PNG composite material introduced in this study paved the way for future advancements in wide color gamut and ultra-high definition backlight display technologies.

Effect of B2O3/SiO2 ratio on photoluminescence properties and stability of red-emitting CsPb(Br/I)3 borosilicate quantum dots glass

Effect of B2O3/SiO2 ratio on photoluminescence properties and stability of red-emitting CsPb(Br/I)3 borosilicate quantum dots glass

Highly Humidity-Resistant Oxynitride Phosphor BaSi6N8O:Ce3+ for pc-LEDs.

Many phosphor hosts, for example, nitrides and sulfides, often face challenges such as hydrolysis and oxidation, limiting their application in phosphor-converted white light-emitting diodes (pc-LEDs). In this study, we developed a highly humidity-resistant yellow-green-emitting phosphor BaSi6N8O:Ce3+ (BSNO:Ce3+). The DFT calculations revealed a high Debye temperature (ΘD = 1159 K), indicating a rigid crystal structure that contributes to the photoluminescence thermal quenching resistance of BSNO. Furthermore, we observed a notable positional shift of Ce3+ in the BSNO lattice, contributing to an unusual photoluminescence (PL) red shift compared to BSNO:Eu2+. Importantly, BSNO:Ce3+ exhibited remarkable PL stability under harsh conditions, showing no degradation in water for 10 days and less than 10% intensity loss at elevated temperatures up to 773 K. We constructed a prototype white LED with a high color rendering index (Ra = 92) by combining a 365 nm chip with BSNO:0.03Ce3+ and commercial phosphors, demonstrating its potential for advanced pc-LED applications.

Insights into glucose-derived carbon dot synthesis via Maillard reaction: from reaction mechanism to biomedical applications

Carbon dots (CDs) are versatile nanomaterials that are considered ideal for application in bioimaging, drug delivery, sensing, and optoelectronics owing to their excellent photoluminescence, biocompatibility, and chemical stability features. Nitrogen doping enhances the fluorescence of CDs, alters their electronic properties, and improves their functional versatility. N-doped CDs can be synthesized via solvothermal treatment of carbon sources with nitrogen-rich precursors; however, systematic investigations of their synthesis mechanisms have been rarely reported. In this study, we developed a method to synthesize N-doped CDs using the Maillard reaction with glucose and ethanolamine as precursors (namely, G-CDs). Comprehensive characterization of these G-CDs revealed the successful incorporation of nitrogen- and glucose-like functionalities. The optical properties and electronic band structures of G-CDs were analyzed using transient absorption and time-resolved photoluminescence spectroscopy. The prepared G-CDs demonstrated near-infrared photoluminescence, low cytotoxicity, glucose transporter-facilitated cellular uptake, and effective heat generation under an 808-nm laser. Particularly, the cellular uptake of G-CDs was reduced by up to 25% after preincubation with a Glut1 inhibitor. These features are suitable for in vitro biological imaging and photothermal therapy in prostate cancer cells. This paper highlights the potential of G-CDs in clinical applications owing to their multicolor emission, photothermal conversion functionality, and versatile surface structure.

Stable and Tunable Photoluminescence Emission of Functionalized Carbon Dots for Heavy Metal Ion Detection

Stable and Tunable Photoluminescence Emission of Functionalized Carbon Dots for Heavy Metal Ion Detection

Tailoring Molecular Space to Navigate Phase Complexity in Cs‐Based Quasi‐2D Perovskites via Gated‐Gaussian‐Driven High‐Throughput Discovery

AbstractCesium‐based quasi‐2D halide perovskites (HPs) offer promising functionalities and low‐temperature manufacturability, suited to stable tandem photovoltaics. However, the chemical interplays between the molecular spacers and the inorganic building blocks during crystallization cause substantial phase complexities in the resulting matrices. To successfully optimize and implement the quasi‐2D HP functionalities, a systematic understanding of spacer chemistry, along with the seamless navigation of the inherently discrete molecular space, is necessary. Herein, by utilizing high‐throughput automated experimentation, the phase complexities in the molecular space of quasi‐2D HPs are explored, thus identifying the chemical roles of the spacer cations on the synthesis and functionalities of the complex materials. Furthermore, a novel active machine learning algorithm leveraging a two‐stage decision‐making process, called gated Gaussian process Bayesian optimization is introduced, to navigate the discrete ternary chemical space defined with two distinctive spacer molecules. Through simultaneous optimization of photoluminescence intensity and stability that “tailors” the chemistry in the molecular space, a ternary‐compositional quasi‐2D HP film realizing excellent optoelectronic functionalities is demonstrated. This work not only provides a pathway for the rational and bespoke design of complex HP materials but also sets the stage for accelerated materials discovery in other multifunctional systems.

Investigation of spin defects in hexagonal boron nitride generated via ion implantation

Spin-active defects in layered hexagonal boron nitride (hBN) crystals have attracted increased attention in quantum sensing. Notably, the recently discovered negatively charged boron vacancy (V B −) center stands out due to its optical addressability and coherent controllability. Among the various methods reported for generating such defects, ion implantation is notable as a readily accessible technique. In this paper, the properties of V B − defects in hBN generated via ion implantation are extensively studied. We achieve a ubiquitous distribution of highly stable defects across the crystal sample, and find that the ion beam current density, rather than fluence, plays a critical role in determining the uniformity and density of defects. The generated defects display bright and stable photoluminescence, and we explicitly investigate the dependence of spin properties on factors such as laser, microwave power, and duration. An intriguing phenomenon is observed wherein the peak contrast exceeds 20% without any enhancing techniques in the optically detected magnetic resonance spectrum for some special defects. Our results provide valuable insights and suggestions for the controlled generation of V B − defects in hBN through ion implantation.

Sodium doped CsPbI3-PMMA composite electrospun fibrous membranes for aqueous photocatalyst and LED

All-inorganic CsPbI3 halide perovskite nanocrystals exhibit excellent photoluminescent properties, but their ambient instability presents a challenge. Adding dopants has been an effective way to improve stability. However, very few work was done for CsPbI3, which is relevant for optoelectronic and photovoltaic applications. Here sodium doped CsPbI3 nanocrystals were precipitated in situ in PMMA polymer matrix at room temperature using an electrospinning technique. It was found that the sodium doping improved the photoluminescence intensity and stability of Na-doped CsPbI3@PMMA electrospun fibrous membranes (EFMs) both in air and in water with an optimal concentration of Na/Pb = 0.75. It is speculated that sodium doping creates a core–shell structure with the sodium passivates the shell while the emission wavelength of the core blue-shifts due to the quantum confinement effect. Furthermore, EFMs can be used as photocatalysts to degrade methyl orange and to create white-LED with CIE of (0.2935, 0.3304) and color temperature of 7227 k.

Addressable planar arrays of highly-luminescent 1,4-bis(5-phenyloxazol-2-yl)benzene nanowires via mask-confined graphoepitaxy for optoelectronic applications

This study introduces a facile method for the controlled growth of addressable planar arrays of highly luminescent, catalyst-free 1,4-bis(5-phenyloxazol-2-yl)benzene (POPOP) nanowires. By employing a hollow mask over a faceted sapphire substrate, simultaneous control over the position and orientation of the nanowires is achieved through a mask-confined graphoepitaxial growth, offering substantial advantages over traditional post-growth assembly techniques. High-temperature annealing creates parallel nanogrooves on the sapphire surface, inducing a graphoepitaxial effect that aligns the nanowires with a consistent [102] crystallographic axis. The hollow mask further aids in precisely localizing nanowire growth through its shadowing effect. Optoelectronic investigations reveal that these nanowires emit intense and stable blue photoluminescence at room temperature, with a broad spectrum spanning from 400 to 600 nm. This luminescence is achieved through excitation by continuous-wave ultraviolet light or two-photon absorption using femtosecond infrared light. Notably, the emission quantum efficiency of POPOP nanowires reaches 59 %, a remarkable improvement over the 12 % observed in powder counterparts when excited with 405 nm light. Transit absorption spectra indicate that ground state bleaching and excited state absorption display consistent kinetics within a 100 ps time window, suggesting the same origin from singlet excitons. The precise alignment and positioning of these nanowires make them viable for in-situ integration into photodetectors with rapid ultraviolet light responses. This study advances the controlled growth of catalyst-free nanowire arrays and enhances the understanding of the optoelectronic properties of POPOP nanowires.

Atomic Layer Deposition for Stable InP-Based On-Chip Quantum Dot microLEDs: Hybrid Quantum Dot Pockets.

Recent advances in synthesis techniques yield InP-based QDs with optical properties comparable to those of benchmark Cd-based QDs, making InP-based QDs viable alternatives to toxic Cd-based QDs for applications such as quantum dot LEDs (QLEDs). However, QLEDs typically suffer from a loss of luminescence over time due to exposure of the QDs to ambient air. To avoid this, state-of-the-art hybrid barrier layers are explored consisting of alternating organic/inorganic layers. In this study, InP-based QD thin films and InP-based QDs embedded in Kraton polymers are encapsulated with a thin metal oxide barrier layer by atomic layer deposition (ALD). Specifically, Al2O3, TiO2, and ZnO thin films are deposited using trimethylaluminum (TMA), tetrakis(dimethylamino)titanium (TDMAT), and diethylzinc (DEZ), with H2O as the reactant. In situ photoluminescence (PL) is used to evaluate the optical response of the InP-based QDs during the ALD coating. The results show that ALD on pristine QD thin films causes degradation of luminescence, while this is not observed for polymer-embedded QDs. The long-term stability of the (ALD-coated) samples is investigated by accelerated degradation in a humidity chamber at a high temperature. Using a single Al2O3 ALD thin film as a capping layer for polymer-embedded QDs, greater stability of the QD-PL over a period of at least 300 h is found compared to pristine QD samples. A similar study is performed with InP-based QDs embedded in UV-patterned polymer (thiol-ene) structures, the so-called QD pockets, envisioned for use in on-chip quantum dot microLEDs. These QD pockets are purposefully designed for pick-and-place operations to reduce the complexity of the on-chip quantum dot microLED manufacturing process. The PL stability was significantly improved after incorporating Al2O3 ALD thin films, with these hybrid QD pockets showing no clear signs of degradation after 140 h. The combination of polymer embedding and ALD with the merits and scalability of the QD pocket structure is demonstrated to be an effective approach to improving the long-term QD stability and shows promise for the development of stable, InP-based on-chip quantum dot microLEDs.

Simple synthesis of AgInS2/ZnS core/shell quantum dots with wide tunable emission wavelength for white light-emitting diodes

Phosphor with efficient and broad range emission is necessary for lighting applications. I-III-VI group quantum dots (QDs) have the advantages of non-toxic composition and large adjustable spectrum range, and have potential applications in the field of lighting. However, the efficient luminescence of these QDs at shorter wavelengths still needs further study, which is crucial for the development of high color rendering index white light LED devices (WLEDs). In this work, wide visible range emitting AgInS2/ZnS QDs with broad band and high luminous efficiency were obtained by altering the Ag/In ratios and Zn2+ inter-diffusion with cation of AgInS2. Photo-luminescent (PL) wavelength range of the obtained core-shell structured AgInS2/ZnS extended from 703 nm to 524 nm with high PL quantum yield (QY) and stability. The champion device based on the optimized AgInS2/ZnS QDs exhibits warm white light (correlated color temperature = 3652 K) characteristics with high color rendering index (CRI Ra) of 92.85 while maintaining excellent color stability under different driving currents. These properties are far superior to those of WLEDs with YAG phosphor.

Photoluminescence Intensity Enhancement and Stability in CdTe/SiO2 Quantum Dots through Water Molecule Adsorption and Trap Passivation

Photoluminescence Intensity Enhancement and Stability in CdTe/SiO2 Quantum Dots through Water Molecule Adsorption and Trap Passivation

Sulfur quantum dots stabilized by myristyl trimethylammonium bromide

For the first time, sulfur quantum dots (SQDs) were obtained in the presence of the cationic surfactant myristyl trimethylammonium bromide (MTAB) using two approaches: “bottom-up” and “top-down”. The synthesis of SQDs from sodium thiosulfate in presence of MTAB required 2 h heating at 70 °C resulting in a solution with stable photoluminescence (quantum yield 18 %). SQDs from sulfur were fabricated during 12 h heating only after etching by hydrogen peroxide. It has been established that the hydrogen peroxide is ineffective agent for SQDs syntheses from sodium thiosulfate (“bottom-up” technique).

In Situ Fabrication of Highly Efficient and Stable Cs2NaInCl6: Sb3+@PVDF Composite Films for Optoelectronic Devices.

Lead-free double perovskites (DPs) have superior phase stability and optical properties, which make them competitive for future applications in illumination and displays. However, the preparation of DPs was mainly based on high-temperature heating and hydrochloric acid as a solvent to form powders, which increased the risk and cost of the preparation process and limited its further application. In this study, the growth of Cs2NaInCl6: Sb3+ DPs in polyvinylidene difluoride (PVDF) films was achieved using an in situ fabrication strategy with DMSO as the solvent. The prepared Cs2NaInCl6: Sb3+@PVDF composite films (CFs) can achieve a bright blue emission under 302 nm irradiation. To achieve the optimal luminescent performance of CFs, the photoluminescence (PL) intensity of Cs2NaInCl6: Sb3+@PVDF CFs under various in situ preparation conditions was compared. In addition, the photoluminescence quantum yield (PLQY) of CFs was increased from 0.72% to 83.77% by adjusting the doping amount of Sb3+, and the fluorescence lifetimes t1 and t2 were 131.08 and 1048.52 ns, respectively. Temperature-dependent PL spectroscopy and density functional theory (DFT) calculations indicate that these excellent optical properties are derived from the self-trapped excitons (STEs) at the [SbCl6]3- octahedron and [InCl6]3- octahedron connected via Cl-Na-Cl. The CFs also demonstrated excellent environmental stability, maintaining a relatively stable PL intensity even under conditions of water immersion, high temperatures, and ultraviolet (UV) radiation. Finally, we used the CFs to assemble a blue light-emitting device (LED), which showed good and stable blue emission performance at different currents. This work can provide a new idea for preparing DPs, which is conducive to promoting their commercial application in high-performance optoelectronic devices.

CsPbBr3@PbSO4 nanocomposites with near-unity photoluminescence and ultrastability via in-water in situ embedding synthesis strategy

Perovskite quantum dots (PQDs) are emerging as promising nanomaterials for optoelectronic applications. However, developing a cost-effective green synthesis process that simultaneously possesses satisfactory photoluminescence quantum yield (PLQY) and stability remains a severe challenge. Here, CsPbBr3@PbSO4 nanocomposites with a near-unity PLQY of 99.8 % and robust ambient stability are synthesized in situ in water via 4-Bromobenzenesulfonic acid and ditetradecylamine ligands. Notably, these nanocomposites show no decline in PLQY even after being immersed in water for over 250 days, and also exhibit superior stability against heating, ultrasonication, UV irradiation, anion exchange, and erosion by polar solvents. First-principles calculations reveal that CsPbBr3@PbSO4 nanocomposites can form a natural quantum well structure, which effectively promotes the radiative recombination of carriers in CsPbBr3 QDs. Meanwhile, the remarkable stability is attributed to the ultrahigh decomposition enthalpy of PbSO4 that serves as a strong barrier preventing the invasion of anions and polar media into the embedded CsPbBr3 QDs. Finally, besides the convenient application of green fluorescent paper, a fingerprint recognition is demonstrated by fabricating a bright-green LED integrated with the CsPbBr3@PbSO4 nanocomposites powder and a commercial UV chip. This work provides a new strategy for green synthesis and practical application of high-efficient and ultrastable PQDs.

High photoluminescence quantum yield and stability achieved by encapsulating MAPbBr3 QDs in UIO-66 and their application in LEDs.

Lead halide perovskite quantum dots (QDs) have been extensively studied due to their excellent photoelectric performance. However, the stability of MAPbBr3 QDs is affected by inevitable factors such as light, heat, and moisture, which limits their practical applications. In this work, stable metal-organic framework UIO-66 was synthesized via a solvothermal method, and the composite MAPbBr3@UIO-66 was prepared through an in-situ growth method. Owing to the wide bandgap, small pore size, and regular geometric structure, UIO-66 can confine the size and uniformity of the perovskite QDs encapsulated within the framework, maximally preserving the luminescent properties of the perovskite QDs. Furthermore, UIO-66 isolates the perovskite QDs from contact with polar water molecules in the air, significantly enhancing the stability of the perovskite QDs. The synthesized composite material exhibits high stability and excellent optical performance, with a photoluminescence quantum yield (PLQY) of up to 78.9% in an air environment. After being stored under natural conditions for 35 days, it still retains 65% of its high luminescence intensity and fluorescence quantum efficiency. When packaged into green and white LEDs, the LEDs demonstrate high brightness and good monochromaticity, maintaining stable brightness even after 2.5 hours of continuous operation. These superior characteristics indicate that the composite material MAPbBr3@UIO-66 has great potential for application in LED technology.