Color-tunable Emission Research Articles

Blue-emitting perovskite nanocrystals with enhanced optical properties through using NaBH4

APbX3-type [A = CH3NH3 + (MA+), NH2CH=NH2 + (FA+), X = Cl–, Br–, I–] organic–inorganic perovskite nanocrystals (PeNCs) have superior optical properties, such as emission with a narrow full width at half maximum and emission color tunability over the entire visible range. However, blue-emitting PeNCs [APb(Br/Cl)3] exhibit low photoluminescence quantum yields owing to Cl defects, hindering their practical applications. The Cl defects induce nonradiative recombination caused by the trap levels formed deep in the band gap. Herein, we report the preparation of blue-emitting PeNCs that exhibit excellent optical properties by using NaBH4 to decrease the number of Cl defects.

Regulating room temperature phosphorescence of carbazole quaternization pyridine in polymer through Hofmeister effect

AbstractHofmeister effect is a famous physical chemistry phenomenon that was reported a hundred years ago, which firstly refers to the action of certain salts to decrease the solubility of proteins while others increase. The Hofmeister effect on the luminescent properties of cationic organic fluorophore is still obscure, especially for their room temperature phosphorescence (RTP). Herein, hydrophilic groups (quaternization pyridine) were introduced into carbazole molecules to obtain a series of carbazole derivatives (named CZ‐Py+) with different counter anions in the Hofmeister series. These carbazole derivatives displayed tunable fluorescent color from cyan to yellow in the solid state following the Hofmeister sequence and anti‐Hofmeister behavior in an aqueous solution. Moreover, RTP material with tunable emission color and lifetime was achieved by doping CZ‐Py+ with Hofmeister series anion in polymethyl methacrylate and polyvinyl alcohol, which displayed good performance in time getting information encryption and anti‐counterfeiting.

Tunable emission color of novel Y3NbO7:xDy3+ phosphor

Powders of Y3NbO7:xDy3+ (x = 0.5, 1, 1.5, 3 and 5 mol%) were produced through a solid-state process. X-ray diffraction investigations confirm the fluorite-type structure (space group 𝐹𝑚3̅𝑚) of powders with crystallite size in the range of 19–60 nm. Both the photoluminescence excitation and emission spectra revealed the presence of defects within the material. With different excitation wavelengths, the emission spectra exhibited distinct emission patterns. At each excitation wavelength, the emission was quenched at Dy3+ concentration higher than 1 mol%. The decay time measurements of the highest intensity emission revealed a progressive decrease from 0.472 milliseconds for x = 0.5 mol% to 0.246 milliseconds for x = 5 mol%. The CIE chromaticity coordinates investigation revealed that the emission color may be altered by varying the excitation wavelength, ranging from blue (excitation at 333 nm) and near-white (excitation at 353 nm and 390 nm) to orange (excitation at 457 nm). The chromaticity of emission under 353 nm and 390 nm excitation validated the material's suitability as an almost-white phosphor.

Optical Property Control by the Interligand Charge Transfer Excited State in Brominated Homoleptic and Heteroleptic Aluminum Dinuclear Triple-Stranded Helicates.

The utilization of aluminum, an abundant and inexpensive element, for the synthesis of novel functional complexes is extremely important, but the design and control of photofunctionality are still unexplored. In this study, we focused on our previously developed dinuclear triple-stranded helicates incorporating two aluminum ions (ALPHY) to synthesize both homoleptic and heteroleptic complexes with bromine atoms at the 3-position of the pyrrole moiety in the Schiff base ligands. The brominated Schiff base ligands were reacted with AlCl3 to synthesize homoleptic complexes, while different ligands were mixed to prepare heteroleptic complexes. Single-crystal X-ray structural analysis revealed the structures of these novel complexes. We found that increasing the degree of bromination resulted in a tunable emission color, shifting progressively from 550 (yellow) to 566 nm (orange). Optical resolution of the complexes facilitated the observation of mirror-image circular dichroism and circularly polarized luminescence. Furthermore, employing ultrafast spectroscopy techniques, we have elucidated that the optical properties are governed by the interligand charge transfer (ILCT) among the three ligands. The formation of heteroleptic complexes induces the ILCT state even in nonpolar environments, thereby accelerating nonradiative decay and intersystem crossing. These findings mark significant advancements in photofunctional materials based on multinuclear complexes.

Rational Design of Pyrido[3,2-b]indolizine as a Tunable Fluorescent Scaffold for Fluorogenic Bioimaging.

Novel fluorescent scaffolds are highly demanding for a wide range of applications in biomedical investigation. To meet this demand, the pyrido[3,2-b]indolizine scaffold was designed as a versatile organic fluorophore. With the aid of computational modeling, fluorophores offering tunable emission colors (blue to red) were constructed. Notably, constructed fluorophores absorb lights in the visible range (>400 nm) despite their small sizes (<300 g/mol). Among the fluorophores was discovered a highly fluorogenic fluorophore with a unique turn-on property, 1, and it was developed into a washing-free bioprobe for visualizing cellular lipid droplets in living cells. Furthermore, motivated by the core's compact size and structural analogy to indole, unprecedented tryptophan-analogous fluorogenic unnatural amino acids were constructed and incorporated into fluorogenic peptide probes for monitoring peptide-protein interactions.

Electrochemical and photoluminescence properties of Zinc vanadate nanoparticles synthesized via chemical and green mediated route

Zinc vanadate (Zn2V2O7) nanoparticles (NPs) are successfully synthesized through a solution combustion method, employing Menthaspicata leaves extract as a reducing agent (ZVP) and urea as a chemical fuel (ZVU). Subsequently, the resulting NPs undergo calcination at 600 °C for a duration of 3 h. The pure orthorhombic crystal structure with Cmce space group Bragg reflections are observed in ZVP NPs. However, along with pure orthorhombic phase, few planes corresponding to V2O5 are observed. Green extract helps to retain the single orthorhombic phase. Irregular shaped and bigger sized NPs are observed in ZVU whereas in ZVP, few hexagonal and irregular sized NPs gets decorated on the bigger sized NPs. Better crystalline structure and shape are observed in ZVP compared to ZVU. Transmission electron microscopy analysis matches well with the XRD results. The selected area electron diffraction pattern of ZVP confirms the formation of purity of the sample. The direct energy band gap estimated from the Wood and Tauc’s plot was found to be 3 and 3.04 eV for ZVU and ZVP NPs respectively. The photoluminescence experiment was carried out at 290 and 310 nm excitation wavelengths. As excitation wavelength changes, tuning of emission color is observed from blue to red region. This tuning of color is observed in CIE plot. The CCT value clearly indicates that the samples excited under 290 nm can be utilized for cool LEDs whereas, the sample excited under 310 nm can be utilized for warm LEDs. Thus, the synthesized Zinc vanadate NPs might be the promising candidates for warm/cool display technologies as a nanophosphor based on the excitation wavelength. The electrochemical studies and the capacitance process was evaluated in a 1.0 M Na2SO4 solution utilizing a specific three-electrode setup. The calculated specific capacitance values exhibited variability within the range of 56.8 to 89.7 F/g at scan rates ranging from 10 to 100 mV.

Photoluminescence of Platinum(II) Complexes with Diazine-Based Ligands.

In the last past twenty years, research on luminescent platinum (II) complexes has been intensively developed for useful application such as organic light emitting diodes (OLEDs). More recently, new photoluminescent complexes based on diazine ligands (pyrimidine, pyrazine, pyridazine, quinazoline and quinoxaline) have been developed in this context. This review will summarize the photophysical properties of most of the phosphorescent diazine Pt(II) complexes described in the literature and compare the results to pyridine analogues whenever possible. Based on the emission color, and the photoluminescence quantum yield (PLQY) values, the relationship between structure modification, and photophysical properties are highlighted. Tuning of emission color, quantum yields in solution and solid state and, for some complexes, aggregation induced emission (AIE) or thermally activated delayed fluorescence (TADF) properties are described. When emitting OLEDs have been built from diazine Pt(II) complexes, the external quantum efficiency (EQE) values and luminance for different emission wavelengths and in some cases, chromaticity coordinates obtained from devices, are given. Finally, this review highlights the growing interest in studies of new luminescent diazine Pt(II) complexes for OLED applications.

Glass Disorder Modulated Luminescence in Zero-Dimensional Antimony-Chloride Coplanar Dimers for Optical Anti-counterfeiting.

Zero-dimensional metal halides have received wide attention due to their structural diversity, strong quantum confinement, and associated excellent photoluminescence properties. A reversible and tunable luminescence would be desirable for applications such as anti-counterfeiting, information encryption, and artificial intelligence. Yet, these materials are underexplored, with little known about their luminescence tuning mechanisms. Here we report a pyramidal coplanar dimer, (TBA)Sb2Cl7 (TBA = tetrabutylammonium), showing broadband emission wavelength tuning (585-650 nm) by simple thermal treatment. We attribute the broad color change to structural disorder induced by varying the heat treatment temperatures. Increasing the heating temperature transitions the material from long-range ordered crystalline phase to highly disordered glassy phase. The latter exhibits stronger electron-phonon coupling, enhancing the self-trapped exciton emission efficiency. The work provides a new material platform for manifold optical anti-counterfeiting applications and sheds light on the emission color tuning mechanisms for further design of stimuli-responsive materials.

Tunable emission color from lead-free zero-dimensional Mn2+-doped Cs3InCl6 single crystals

In recent years, the magneto-optical properties of zero-dimensional metal halides have attracted widespread interest. In this study, we employed a vacuum solid-state reaction method to synthesize zero-dimensional, lead-free, and all-inorganic Cs3InCl6 single crystals (SCs). In addition to the blue emission of self-trapped excitons (STEs) inherent to pristine Cs3InCl6, the strategic doping with Mn2+ ions not only facilitates multicolor emissions but also significantly boosts the photoluminescence quantum yield (PLQY) from a modest 1.21 % to an impressive 32.18 %. We carried out an exhaustive investigation into the fundamental mechanisms responsible for these multicolor emissions and the intricate compositional transitions that ensue. Furthermore, the pronounced correlation between temperature-dependent photoluminescence (PL) and magnetic characteristics unveiled the genesis of ferromagnetism within both the pristine and Cs3InCl6: xMn2+ samples. The doping-induced modifications in magnetic behavior furnish a coherent explanation for the anomalous inverse temperature dependence emission wavelength shift. Our research highlights the adjustable PL and magnetic attributes of Mn2+ doped Cs3InCl6, yielding invaluable insights that are poised to advance its application in the next wave of optoelectronic and magnetic technologies.

Intrinsic defective long-persistent luminescence from organic-inorganic hybrid halide perovskite for multiple information encryption

As result of spin-forbidden transition for triplet exciton, the afterglow lifetime of OIHPs was limited to a few seconds. Herein, color-tunable emissions and LPL at room temperature are successfully achieved in (C4H6N3O)2InCl5·H2O OIHP. The prepared (C4H6N3O)2InCl5·H2O exhibit three distinct emissions peaks at 400 nm, 450 nm, and 480 nm, which are revealed from the dynamic transformation from the keto form to the enol from through the ESIPT process. Notably, the (C4H6N3O)2InCl5·H2O singe crystals perform green LPL with a long duration of 15000 s at room temperature. In-depth theoretical calculations and experimental studies suggest that intrinsic defects of (C4H6N3O)2InCl5·H2O introduce trap states that store the charge carrier and release them to the triplet state of organic components of (C4H6N3O)2InCl5·H2O to achieve LPL. This work offers a valuable method for increasing LPL duration for its triplet exciton in OIHPs by introducing intrinsic defective. Finally, the good stability and optical information encryption application of (C4H6N3O)2InCl5·H2O are demonstrated.

Modification of Local Site Preference for Achieving Tunable Color Emission from Blue to Near-White in Sr3(PO4)2:Dy3+ Phosphor

The color tunability of Sr3(PO4)2:1%Dy3+ phosphor from blue to near white is studied at various annealing conditions. Higher temperature annealing promotes agglomerated rhombohedral (α) phase formation. Experimental and theoretical analysis reveal dopant preference at the low-symmetry Sr(II) site, altering electric (4F9/2→6H13/2) and magnetic (4F9/2→6H15/2) dipole transitions, thereby affecting the yellow-to-blue (Y/B) ratio. The luminescence intensity variation and color tunability are explained based on the local site symmetry and occupation probability of the dopant in the host lattice. An increase in the luminescence intensity up to an annealing temperature of 1200 °C, followed by quenching is observed due to the oxygen vacancies. Commission Internationale d'Eclairage (CIE) color coordinates of (0.31, 0.38), Correlated Color Temperature (CCT) of 6341 K, and color purity of 22.57% confirm the potential of Sr3(PO4)2:1%Dy3+ phosphor annealed at (1200 °C, 6 hrs) for white light generation. A probable photoluminescence mechanism involving 4f→5d→4f transitions in Sr3(PO4)2:1%Dy3+ is proposed.

Color-tunable fluorescence and ultralong organic room temperature phosphorescence from multicomponent copolymers

Materials with color-tunable photoluminescence (PL) have attracted dramatically increasing interest in recent years, especially the tuning of both fluorescence (FL) and ultra-long organic room temperature phosphorescence (UOP). Herein, a series of polymer films are successfully fabricated by in situ copolymerization of carbazole derivatives, lanthanide complex, and acrylamide (AM). With a long lifetime of 2.82 s and a high quantum yield of 21.40%, these copolymers exhibit not only color-tunable FL from violet-red to blue, but also multicolor UOP scope from blue to chartreuse when the excitation wavelength is changed. Moreover, a nearly-white phosphorescence can also be observed by adjusting the excitation wavelength. Multiple information patterns with color-tunable FL and UOP emissions are captured, exhibiting promising potential in the information encryption and anti-counterfeiting fields.

Near-unity quantum yield and long-term emission stability in halide perovskite nanocrystal glass composite

Metal halide perovskites are promising optoelectronic materials due to their outstanding luminescent properties. However, the instability of perovskites has long been the bottleneck to their practical applications. Here Cs4PbBr6 nanocrystals based glass composite (Cs4PbBr6 NCs@glass) are successfully prepared, which displays green emission color (520 nm), narrow bandwidth (23 nm) and a near-unity photoluminescence quantum yield (PLQY). The H2O molecules permeating in the lattice of Cs4PbBr6 were found to be a crucial role in the subband energy emission. The Cs4PbBr6 NCs@glass has excellent emission stability; maintains 93 % of initial PL intensity after ultraviolet light irradiation for over 5000 h. In addition, by adjusting the halogen content, we have achieved tunable emission color from blue (450 nm) to green (520 nm) and red (670 nm) on Cs4PbX6 NCs@glass (X = Cl, Br, I), which covers up to 127 % of the National Television Systems Board (NTSC) standard system. Our finding indicates the commercial applications of perovskite materials in lighting and display.

The crystal structure, energy transfer and tunable luminescence properties of NaLaMgWO6:Tm3+, Eu3+ phosphors

A series of NaLaMgWO6:Tm3+, Eu3+ phosphors with color-tunable emission were successfully synthesized by the solid-state reaction method. The crystal structure, luminescence characteristics and energy transfer of NaLaMgWO6:Tm3+, Eu3+ phosphors have been studied. It is observed that Tm3+ singly doped phosphors exhibit intense blue emission at 484 nm, and Eu3+ singly doped phosphors emit red light at 621 nm. The phosphors co-doped with Tm3+, Eu3+ exhibit fluorescence spectra composed by the characteristic emission peaks of Tm3+ ions and Eu3+ ions. A tunable emission color from blue to red can be obtained by adjusting the ratio of the doping concentration of Tm3+/Eu3+, indicating a significant energy transfer from Tm3+ to Eu3+. The energy transfer mechanism between Tm3+→Eu3+ in the NaLaMgWO6:Tm3+, Eu3+ phosphors is proved to be a quadrupole-quadrupole interaction. These results show that NaLaMgWO6:Tm3+, Eu3+ phosphors may have a potential application in white light emitting diodes.

Overcoming Challenges in OLED Technology for Lighting Solutions

In academic research, OLEDs have exhibited rapid evolution thanks to the development of innovative materials, new device architectures, and optimized fabrication methods, achieving high performance in recent years. The numerous advantages that increasingly distinguish them from traditional light sources, such as a large and customizable emission area, color tunability, flexibility, and transparency, have positioned them as a promising candidate for various applications in the lighting market, including the residential, automotive, industrial, and agricultural sectors. However, despite these promising attributes, the widespread industrial production of OLEDs encounters significant challenges. Key considerations center around efficiency and lifetime. In the present review, after introducing the theoretical basis of OLEDs and summarizing the main performance developments in the industrial field, three crucial aspects enabling OLEDs to establish a competitive advantage in terms of performance and versatility are critically discussed: the quality and stability of the emitted light, with a specific focus on white light and its tunability; the transparency of both electrodes for the development of fully transparent and integrable devices; and the uniformity of emission over a large area.

Pulsed operation of perovskite LEDs: a study on the role of mobile ions

ABSTRACT Metal halide perovskite light-emitting diodes (PeLEDs) are a promising technology for energy-efficient and cost-effective lighting and displays, thanks to their tunable color emission, high brightness, color purity and low-temperature fabrication. However, the mixed ionic-electronic conductivity of perovskite materials presents unique challenges, as ionic defects can redistribute under operation, affecting the energy landscape and charge recombination mechanisms. Our drift-diffusion simulations establish a connection between the transient electroluminescence (TrEL) signals of PeLEDs under pulsed operation and the influence of mobile ions. We find that the TrEL plateau value’s dependence on the duty cycle and end-of-pulse overshoot can be explained by the time-varying distribution of ionic defects. The inclusion of mobile ions is crucial to understand the TrEL response. Moreover, the simulations highlight injection barriers at the perovskite/charge-transport layer interfaces, such as is the case for the hole transport layer in our example, as a significant source of non-radiative charge recombination. These findings contribute to the understanding of transient ionic processes in perovskite-based devices.

Recent Advances in Fluorescent Polymers with Color-Tunable Aggregate Emission

Recent Advances in Fluorescent Polymers with Color-Tunable Aggregate Emission

Fixed Yellow-to-Blue Intensity Ratio of Dy3+ in KY(CO3)2 Host for Emission Color Tuning.

Dy3+, Ce3+ co-doped KY(CO3)2 phosphors with a monoclinic structure were synthesized using the hydrothermal method to create a fixed yellow-to-blue ratio emission. The [YO8] polyhedron, consisting of a Y atom and eight oxygen atoms, forms a relatively independent microstructure within the KY(CO3)2 host. Y3+ ions are partially replaced by Ce3+ or Dy3+ ions to construct the [CeO8] or [DyO8] polyhedral fluorescence emission unit. The spectral measurements indicate that Ce3+ and Dy3+ can maintain relatively independent fluorescence emission characteristics in the KY(CO3)2 host. The yellow-to-blue intensity ratio of Dy3+ remains close to 1 and does not change with the variation in the doping concentration of KY(CO3)2:Dy3+ and KY(CO3)2:Dy3+,Ce3+ phosphors. When Ce3+ and Dy3+ are co-doped with KY(CO3)2, the emission intensities of Dy3+ under 339 nm and 365 nm excitation increase by 8.43 and 2.32 times, respectively, through resonance energy transfer and cross-relaxation. All Ce3+-doped KY(CO3)2:Dy3+ phosphors can emit white light. Among them, the emitted light of KY(CO3)2:3%Dy3+,5%Ce3+ is closest to standard daylight. Therefore, a stable [YO8] polyhedral structure can be used to achieve more color tuning of light.

Tunable Color Emissions upon UV Irradiation from Tb3+:Y2SiO5 Phosphor

Tunable Color Emissions upon UV Irradiation from Tb3+:Y2SiO5 Phosphor

Multifunctional chitosan-based lanthanide luminescent hydrogel with stretchability, adhesion, self-healing, color tunability and antibacterial ability

Lanthanide luminescent hydrogels have broad application prospects in various fields. However, most of lanthanide hydrogels possess relatively simple functions, which is not conducive to practical applications. Therefore, it is becoming increasingly urgent to develop multifunctional hydrogels. Herein, a multifunctional chitosan-based lanthanide luminescent hydrogel with ultra-stretchability, multi-adhesion, excellent self-healing, emission color tunability, and good antibacterial ability was prepared by a simple one-step free radical polymerization. In this work, our designed lanthanide complexes [Ln(4-VDPA)3] contain three reaction sites, which can be copolymerized with N-[tris(hydroxymethyl) methyl] acrylamide (THMA), acrylamide (AM), and diacryloyl poly(ethylene glycol) (DPEG) to form the first chemical crosslinking network, while hydroxypropyltrimethyl ammonium chloride chitosan (HACC) interacts with the hydroxyl and amino groups derived from the chemical crosslinking network through hydrogen bonds to form the second physical crosslinking network. The structure of the double network as well as the dynamic hydrogen bond and lanthanide coordination endow the hydrogel with excellent stretchability, adhesion and self-healing properties. Moreover, the introduction of lanthanide complexes and chitosan makes the hydrogel exhibit outstanding luminescence and antibacterial performances. This research not only realizes the simple synthesis of multifunctional luminescent hydrogels, but also provides a new idea for the fabrication of biomass-based hydrogels as intelligent and sustainable materials.