Tunable Emission Research Articles

Regulating the continuous and concentrated distribution of Quasi-2D perovskite phases to achieve Sky-Blue Light-Emitting diodes with efficiency approaching 17%

Blue perovskite light-emitting diodes (PeLEDs) are increasingly crucial for manufacturing high-definition full-color displays due to their outstanding electroluminescent properties. Quasi-two-dimensional (quasi-2D) perovskite stands out as the most promising material for blue light-emitting layer, given its robust quantum/dielectric confinement. In this study, we present the preparation of PeLEDs with a tunable blue emission wavelength using pure bromide perovskite components by adjusting the content of halogenated organic ammonium bromide [2-bromoethylamine hydrobromide (BEABr)]. The bifunctional ligand BEABr not only achieves an excellent phase distribution of quasi-2D perovskite but also reduces the weak van der Waals gap between individual perovskite layers, facilitating effective energy transfer in perovskite films. Additionally, the bifunctional groups passivate perovskite defects and inhibit phase separation, leading to efficient and stable sky-blue luminescence. The BEABr-doped sky-blue PeLED demonstrated superior device performance, achieving a maximum external quantum efficiency of 16.98 % at 493 nm. This work serves as inspiration for further exploration of efficient and stable commercial blue PeLED devices.

Laser Dynamic Control of the Thermal Emissivity of a Planar Cavity Structure Based on a Phase-Change Material.

Tailoring the thermal emission of a material in the long-wave infrared (IR) range of 8-13 μm is crucial for many IR-adaptive applications, including personal thermal management, IR camouflage, and radiative cooling. Although various materials and surface structures have been proposed for these purposes, space-selective and dynamic control of their emissivity is challenging. In this study, we present a planar surface cavity structure consisting of a Ge2Sb2Te5 (GST) film on top of a thin metal reflector to modulate its emissivity by using an ultraviolet laser beam. A laser-induced phase change in GST allowed for the local control of emissivity. The average emissivity in the long-wave IR range was tunable from 0.15 to 0.77 simply by changing the laser energy deposited on the GST film. This enabled the laser printing of high-contrast emissivity patterns, which were erasable by subsequent thermal annealing. Emissivity-modulated GST cavities could be fabricated on not only rigid substrates but also flexible plastic substrates such as polyimide. The GST surface cavity was highly flexible and remained stable upon repeated bending to a curvature radius of 0.5 cm. This study provides a promising route for realizing scalable and flexible thermal emitters with tunable surface emissivity.

Bright luminescence from nontoxic all-inorganic low-dimensional cesium halide.

Due to the superiority of low cost, easy manufacture, and tunable light emission owing to the diversity of compositions and dimensionalities, the metal halides have appeared as a promising class of semiconductors. Nevertheless, the toxicity problem along with inherent instability of Pb-based metal halides greatly limits their large-scale applications. Based on this situation, it is necessary to develop eco-friendly materials, which could simultaneously maintain the excellent optoelectronic properties of lead materials. In this Letter, the one-dimensional Cu + -alloyed Cs2AgI3 has been successfully synthesized. An intense blue emission located at 469 nm with a large Stokes shift was observed. Density functional theory calculation indicated that the Cu+ ions could effectively modulate the density of state population, which was the key factor drastically boosting the photoluminescence quantum yield (PLQY). This kind of highly efficient metal halide may overcome the bottlenecks of toxicity and poor efficiency issues of blue emission and will have a promising prospect in the optoelectronic fields.

Antimony Doped Hybrid Zinc Halide Crystals with Tunable Light Emission and Long‐Term Stability

AbstractAs a class of emerging photoluminescent materials, hybrid halide crystals have drawn research attention for their potential application in the fields of light‐emitting, security, and waveguide. Nevertheless, hybrid halide crystals containing antimony with long‐term stability and tunable light emission are still increasingly in demand. In this work, serial new hybrid halide crystals (BZA)2ZnCl4·2H2O:xSb3+ (x = 0–0.2, x represents the reaction ratio) and (BZA)2SbCl5 are synthesized (BZA = 2,4‐diamino‐6‐phenyl‐1,3,5‐triazine). In (BZA)2ZnCl4·2H2O:xSb3+ crystals, Sb3+ cations replace partial Zn2+ cations to form [SbCl4]− tetrahedron. Red light emission caused by the substitution of Sb3+ for Zn2+ enhances as the doping rate increases, resulting in the tunable emission from light blue to pink and finally to dark red. There are two kinds of Sb3+ in (BZA)2SbCl5 crystal. Sb(1) has a sixfold coordination with Cl to form a [Sb(1)Cl5]∞ 1D zigzag chain. Sb(2) atom adopts a fivefold coordination with Cl and is separated from each other by BZA+ cations. (BZA)2SbCl5 crystal shows bright orange‐yellow light emission with a photoluminescence quantum yield of 45%. Moreover, the organic–inorganic hybrid metal halide crystals containing antimony have excellent long‐term stability, with phase and luminescence keeping nearly unchanged after more than six months in ambient air.

Efficient White Light‐Emitting Diodes Based on Cu(I) Activated Single‐Phase Halide Single Crystals

Single‐phase white light emitters have become a potential substitute for tricolor phosphor mixtures for the white light‐emitting diodes (WLEDs) application to simplify device structure and eliminate self‐absorption. Newly developed low‐dimensional halides, noted for their highly efficient luminescent characteristics, have seen increasing interest in recent years. Herein, highly efficient white‐light emission is demonstrated in single‐phase zero‐dimensional halide single crystal, namely monovalent Cu‐doped Cs2HfCl6. Cs2HfCl6:Cu single crystals have three luminescent centers. Two emission peaks at 365 nm and 380 nm correspond to the intrinsic self‐trapped excitons emission and a defect‐related trapped exciton emission, respectively. Cu doping introduces an intense Cu‐bound exciton emission peaking at 540 nm with a large Stokes shift of 250 nm and a high photoluminescence quantum yield of 68%. With different excitation wavelengths and Cu‐doping concentrations, Cs2HfCl6:Cu single crystals show tunable emissions. Under 254 nm ultraviolet light excitation, Cs2HfCl6:0.5%Cu yields cold white light with a high color rendering index (Ra = 87.3). These findings demonstrate the potential of Cs2HfCl6:Cu as a promising phosphor for cold WLEDs.

Optical thermometry and multi-mode anti-counterfeiting based on Bi3+/Ln3+ and Ln3+ doped Ca2ScSbO6 phosphors

A series of novel Bi3+/Ln3+-activated Ca2ScSbO6 (CSSO) phosphors were synthesized by solid-state method and their luminescent behaviors were investigated in detail. Under the 302 nm excitation, the CSSO:Bi3+ shows remarkable near-ultraviolet photoluminescence with a peak emission at 365 nm. Eu3+-activated CSSO phosphor possesses high efficiency and no obvious reduction of emission intensity even after replacing Sc with Eu completely, which indicates a low-concentration quenching effect. In addition, its emission intensity at 423 K (I423K) still maintains 88 % compared with that of at room temperature (I298K), indicating good thermostability. In contrast, the CSSO:Bi3+ phosphor exhibits a significant reduction in emission intensity, maintaining only 49 % of its luminescence at 423 K (I423K/I298K). By codoping Bi3+ and Ln3+ (Ln = Eu, Tb, Dy, Sm), the energy transfer was observed from the Bi3+ to Ln3+ ions, endowing the CSSO:Bi3+, Ln3+ phosphors with tunable multicolor emissions. Leveraging the differing thermostabilities of the emission spectra for Bi3+ and Ln3+ ions, we designed and assessed a range of sensitive optical thermometers. Among these, the CSSO:Bi3+, Eu3+ phosphors exhibited the best performance, boasting maximum absolute and relative sensitivities of 9.96 % K−1 and 2.002 % K−1, respectively. Additionally, we displayed the multi-mode anti-counterfeiting function of synthesized phosphors, and a multi-color switching system was designed with the advantages of direct visualization and easy identification of encrypted information. These results indicate that Bi3+ and Ln3+ coactivated CSSO phosphor has the potential application for non-contact temperature measurement and anti-counterfeiting.

Stimuli‐responsive fluorescent hydrogels: Strategies and applications

AbstractStimuli‐responsive fluorescent hydrogels are three‐dimensional networked polymeric materials with tunable luminescence and dynamic properties, which play an important role as a water‐rich soft material in the fields of information encryption, bionic actuation, bioimaging, environmental monitoring, and luminescent materials. Compared with conventional hydrogels, their unique luminescent properties allow the visualization of microscopic dynamics within the polymer network. By rational inclusion of dynamic motifs, such as photoswitches, AIEgens, lanthanide complexes, and host–guest complexes, these materials are endowed with tunability of emission, shape, and phase in time and space in response to environmental effectors. In this review, we summarize the fabrication strategies that are mainly used by recently reported stimuli‐responsive fluorescent hydrogels and the applications of these materials.

Correction to “Tunable Wavelength, High-Brightness, and NIR-II Emission Phenanthridinium-Based Heptamethine Dyes for High-Contrast Vascular and Intestinal Imaging In Vivo”

Correction to “Tunable Wavelength, High-Brightness, and NIR-II Emission Phenanthridinium-Based Heptamethine Dyes for High-Contrast Vascular and Intestinal Imaging In Vivo”

Tunable emission and energy transfer of B2O3–Bi2O3–AlF3 glass system doped with Eu3+/Dy3+

The structure and luminescent properties of the B2O3–Bi2O–AlF3 glass system doped with Eu3+/Dy3+ ions in different molar ratios were studied. A series of glasses were synthesized by the conventional melt quenching technique. Glass transition and crystallization temperatures were examined by Differential Thermal Analysis (DTA) measurements. The amorphous character of the prepared samples was confirmed by the X-ray diffraction (XRD) method. Raman and FTIR spectra were collected and deconvoluted to investigate the glass micro-structure. Luminescence spectra revealed that the added rare-earth ions can be excited by a single wavelength. The emitted color can be tuned by changing the ratios of the Eu3+/Dy3+ ions and the excitation wavelength. Furthermore, the influence of the addition of AlF3 on the luminescence and decay times was investigated. In the glasses with 10 mol% AlF3 an enhancement of the emission and excitation spectra was detected. The energy transfer analysis confirms the energy transfer between Eu3+ and Dy3+ ions in the glass matrix. Additionally, the results of this study indicate that the B2O3–Bi2O–AlF3 glasses doped with Eu3+ and Dy3+ can be used as a color tunable phosphor.

Dual ligands synergy enables thermal and moisture stability-enhanced blue quasi-2D perovskite for efficient light-emitting diodes

Quasi-2D metal halide perovskite is rising for efficient blue light-emitting diodes due to strong quantum confinement and tunable emission, while a challenge remains in its poor stability of n-phase distribution under external stresses. Herein, the stable blue quasi-2D perovskite under heat and moisture conditions is achieved by dual ligand engineering. The Lewis base moieties − SO3− from taurine (3S) bind tightly with perovskite edges, inhibiting Ostwald ripening of the perovskite phase caused by the heat, and 3, 3-diphenylpropylamine (DPPA) provides a strong hydrophobicity to the perovskite film, suppressing phase disproportionation induced by the moisture. Accordingly, the blue perovskite film, modified synergistically by the 3S and DPPA dual ligands, maintains its initial photoluminescence quantum yield (PLQY) after over 200 h with 70 °C heating, and only exhibiting a redshift in PL peak wavelength less than 10 nm. Exposing under environment condition of 20 % relative humidity for 300 h, the blue perovskite film still retains its initial PL peak wavelength with PLQY exceeding 50 % of the initial value. This achievement establishes a notable strategy for enhancing both the thermal and moisture stability of blue quasi-2D perovskite. Furthermore, the light-emitting diodes based on the perovskite films display the enhanced operating stability. This work offers an efficient strategy for stabilizing blue quasi-2D perovskite and the corresponding devices for the display application.

Tunable light emission of Bi and V-doped borosilicate glasses for application in white light-emitting diodes

Melt-quenched borosilicate glasses, co-doped with Bi and V ions, exhibited broad visible spectrum emissions. Bi ions primarily existed as Bi3+, acting as network modifiers, lowering the glass transition temperature linearly with increasing Bi content. V5+ ions adopted tetrahedral coordination as [VO4]3- units. Photoluminescence of Bi ions is shifted from blue to longer wavelengths with higher Bi content, associated with the stabilization of Bi2+ and the presence of Bi3+ in different local environments. Combined with V ions, the glasses emitted light covering the entire visible spectrum, offering the potential for white LED applications with correlated color temperatures ranging from 6135 to 4010 K. The highest QY was 11.9 and 8.0 % upon excitation at 325 and 340 nm.

Multi-responsive smart fluorophores from pyrazole-functionalized tetraphenylethene AIEgens in response to Hg(II) ion, temperature, and mechanical force

Five tetraphenylethene (TPE) derivatives 1a, 1b, 2, 3, and 4 with adjustable stimuli-responsive characteristics were designed and synthesized in this study. Using single-crystal X-ray diffraction, the effects of substitution positions and pyrazolyl numbers on molecular packing were examined in the solid state. The findings indicate that as the pyrazolyl numbers increased, the molecular packing of the compound progressively changed from the C−H···π stacked compact mode in 1 − 3 to the X-crossing stacked loose mode in 4, which results in the origin of various stimuli-responsive phenomena in compound 4. This approach facilitates the preparation of multi-stimuli-responsive (thermochromism, mechanochromism, and metal ion fluorescence switch) smart fluorophores with tunable emission color. Moreover, compound 4, with an excellent fluorescence performance, exhibited three different colors when reversible mechanochromism was selected as the candidate for an optical recording material and security ink. This study proposes an effective method to guide the design of stimuli-responsive materials, which, in turn, would facilitate the development of high-contrast MC molecules, and the optical information anticounterfeiting based on grinding was proven by utilizing the grind-responsive luminescence capabilities.

Unidirectional ring laser operation and tunable single-frequency emission using differential parametric gain.

In this Letter, a novel approach for unidirectional operation of a 1064 nm solid-state ring laser is demonstrated based on difference frequency mixing. Unidirectional operation is achieved exploiting the directional parametric gain from a single-pass diode laser, facilitated through a periodically poled LiNbO3 crystal. In addition to achieving unidirectional operation, the nonlinear process further enables the generation of single-frequency mid-infrared light. Using a single-pass tapered diode laser, tunable in the range from 780 to 815 nm, the generated mid-infrared signal covers the 2.9 to 3.5 µm range while optimizing the phase-match condition of the difference frequency generation process.

Dynamic Transition between Monomer and Excimer Phosphorescence in Organic Near-Infrared Phosphorescent Crystals.

Achieving efficient near-infrared room-temperature phosphorescence of purely organic phosphors remains scarce and challenging due to strong nonradiative decay. Additionally, the investigation of triplet excimer phosphorescence is rarely reported, despite the fact that excimer, a special emitter commonly formed in crystals with strong π-π interactions, can efficiently change the fluorescent properties of compounds. Herein, a series of dithienopyrrole derivatives with low triplet energy levels and stable triplet states, exhibiting persistent near-infrared room-temperature phosphorescence, is developed. Via the modification of halogen atoms, the crystals display tunable emissions of monomers from 645 to 702nm, with a maximum lifetime of 3.68ms under ambient conditions. Notably, excimer phosphorescence can be switched on at low temperatures, enabled by noncovalent interactions rigidifying the matrix and stabilizing triplet excimer. Unprecedentedly, the dynamic transition process is captured between the monomer and excimer phosphorescence with temperature variations, revealing that the unstable triplet excimers in crystals with a tendency to dissociate can result in the effective quench of room-temperature phosphorescence. Excited state transitions across varying environments are elucidated, interpreting the structural dynamics of the triplet excimer and demonstrating strategies for devising novel near-infrared phosphors.

Metal Halide Perovskites: Promising Materials for Light-Emitting Diodes

Metal halide perovskites have shown excellent optoelectronic properties, including high photoluminescence quantum yield, tunable emission wavelengths, narrow full-width at half-maximums and a low-cost, solution-processed fabrication, which make it exhibit great potential as emission-layer materials of light-emitting diodes. With the joint efforts of researchers from different disciplines, there has been a significant progress in the improvement in the external quantum efficiency (EQE) and stability of perovskite light-emitting diodes (PeLEDs) in recent years, especially in green PeLEDs with EQEs over 30%. However, their operational stability lags behind other commercial organic and chalcogenide quantum dot emitters, limiting their practical application. In this review, we first introduce the basic device structure of PeLEDs, as well as the factors influencing the EQE and stability of PeLEDs. Secondly, the development of lead-based and lead-free PeLEDs are summarized systematically. Thirdly, challenges of PeLEDs are discussed in detail, including low the EQE of blue PeLEDs, poor device stability and EQE roll-off. Finally, some suggestions and perspectives for future research directions for PeLEDs are proposed.

Efficient tunable visible and near-infrared emission in Sb3+/Sm3+-codoped Cs2NaLuCl6 for near-infrared light-emitting diode, triple-mode fluorescence anti-counterfeiting and information encryption

Rare earth ions (RE3+)-doped double perovskites have attracted tremendous attention for its fascinating optical properties. Nevertheless, RE3+ generally exhibits poor photoluminescence quantum yield (PLQY) for their parity-forbidden 4f-4f transition and the low doping concentration. Herein, we reported Sb3+/Sm3+-codoped rare earth-based double perovskite Cs2NaLuCl6 that enables efficient visible and near-infrared (NIR) emission, which stems from self-trapped exciton (STE) and Sm3+, respectively. Benefit from up to 72.89% energy transfer efficiency from STE to Sm3+ and high doping concentrations due to similar ionic activity between Sm3+ and Lu3+, thus eruptive PLQY of 74.58% in the visible light region and 23.12% in the NIR light region can be obtained. Moreover, Sb3+/Sm3+-codoped Cs2NaLuCl6 exhibits tunable emission characteristic in the visible light region under different excitation wavelengths, which can change from blue emission (254 nm excitation) to white emission (365 nm excitation). More particularly, only the NIR emission can be captured by the NIR camera when a 700 nm cutoff filter is added. The excellent stability and unique optical properties of Sb3+/Sm3+-codoped Cs2NaLuCl6 enable us to demonstrate its applications in NIR light-emitting diode, triple-mode fluorescence anti-counterfeiting and information encryption. These findings provide new inspiration for the application of rare earth-based double perovskite in optoelectronic devices.

Multiemission of Ce3+ from a Single Crystallographic Site Induced by Disordering of Ions.

White-light emission with a single activator is an attractive function of phosphors. In this work, we investigated the photoluminescence properties of Ca5.7Y1.3Si7O16.7N3.3, which is a compound denoted as Ca4+xY3-xSi7O15+xN5-x discovered by our group, with Ce-activation using optical measurements and density functional theory (DFT) calculation. Samples showed a tunable emission from purple to white under ultraviolet (UV) light. In this compound, Ca and Y as well as anions are distributed disorderly, and Ca/Y ions occupy two crystallographically distinct sites; those sites are possible sites for Ce substitution. DFT calculation and structural refinement revealed that the tunable emission was generated by Ce at the crystallographically equivalent site but with distinct local structures caused by the disordering of cations and anions. As far as we know, this is the first report about a white-light-emitting phosphor with only Ce activation.

Precise Manipulation the Efficient Multi‐Exciton Emission with High Thermal Stability in Hybrid Manganese‐Antimony Chloride for Optical Thermometry, Anti‐Counterfeiting, and Information Encryption

AbstractRecently, zero‐dimensional (0D) metal halides with highly efficient tunable emission have shown broad prospects in the field of anti‐counterfeiting. However, the limited emission colors and low resolution, as well as the severe thermal quenching of self‐trapped excitons, have greatly constrained their applications. In this study, a high thermal stability compound by precisely manipulating the multi‐exciton emission within Sb‐doped hybrid manganese chloride is developed, which exhibits three emission colors (green, orange, and yellow). It is discovered that this compound exhibits significant color changes in the low‐temperature range. Optical temperature sensing, anti‐counterfeiting, and information encryption models based on this compound are successfully designed. This research proposes an effective strategy for designing novel eco‐friendly and efficient anti‐counterfeiting and temperature sensing materials, paving the way for optical temperature sensing and multi‐key encryption‐decryption applications.

Recent Advances in Organometallic NIR Iridium(III) Complexes for Detection and Therapy.

Iridium(III) complexes are emerging as a promising tool in the area of detection and therapy due to their prominent photophysical properties, including higher photostability, tunable phosphorescence emission, long-lasting phosphorescence, and high quantum yields. In recent years, much effort has been devoted to develop novel near-infrared (NIR) iridium(III) complexes to improve signal-to-noise ratio and enhance tissue penetration. In this review, we summarize different classes of organometallic NIR iridium(III) complexes for detection and therapy, including cyclometalated ligand-enabled NIR iridium(III) complexes and NIR-dye-conjugated iridium(III) complexes. Moreover, the prospects and challenges for organometallic NIR iridium(III) complexes for targeted detection and therapy are discussed.

Simple synthesis of carbon dots/organosilicon composites with tunable solid-state emission and size for accurate latent fingerprint identification

The CDs–OSi composites with tunable emission and size were prepared by adjusting the volume ratio of H2O and EtOH in solvothermal. The CDs–OSi composites were applied in identification of latent fingerprint with effective definition and contrast.