Color Tuning Research Articles

Electrically Responsive Photonic Crystals with Enhanced Suspension Stability and Color Saturation for Electrophoretic Displays and Smart Windows.

Electrophoretic displays (EPDs) based on photonic crystals show great potential due to their reduced eye fatigue and low power consumption. However, the current image quality and service life of this system still face great challenges. In this work, we fabricated a new kind of electrically responsive photonic crystal (ERPC) device based on PSMA@SiO2 liquid colloidal crystals (LCCs) for EPDs. By introduction of the PSMA core with lower density and higher refractive index, the suspension stability and color saturation of PSMA@SiO2 LCCs were greatly enhanced compared with those of bare SiO2 LCCs. The PSMA@SiO2 LCCs showed brilliant colors, wide color tuning range (∼200 nm), and good reversibility under low voltages (<4 V). Interestingly, the transparency of PSMA@SiO2 LCCs could also be obviously regulated by an electric field, which was different from the traditional ways that change the thickness of PCs or contrast of refractive index (Δn) between the nanospheres and matrix. This transparency modulation offered a novel idea for the transmittance control of smart windows. As a proof of concept, we fabricated a new type of patterned ERPC device to demonstrate their potential in electrophoretic displays and smart windows with controllable transmittance under an electric field.

Tunable Multicolor Emission and High Thermal Stability in Single‐Matrix Luminescent Crystals Based on Calcium Perovskites for Advanced Solid‐State Lighting Applications

AbstractThe development of environmentally friendly full‐inorganic luminescent materials with tunable emission properties and exceptional thermal stability is of paramount importance for applications in optoelectronic devices, solid‐state lighting, and anti‐counterfeiting technologies. In this study, a novel luminescent crystal based on calcium perovskites Cs2CaCl4·2H2O (CCCH) are explored using a hydrothermal method. Simultaneous co‐doping of CCCH with Sn2+ and Mn2+ yields the s‐p transition‐induced cyan light from Sn2+ and d‐d transition‐induced yellow light from Mn2+. It demonstrates effective energy transfer from self‐trapped exciton (STE) of matrix CCCH and s‐p transition of Sn2+ to Mn2+, synergizing composite white lights with tunable colors. Furthermore, the incorporation of Sn2+ into CCCH introduces a red shift from blue to cyan emission with a remarkable enhancement in luminescent intensity by a factor of 12 times. The crystal orbital Hamiltonian populations (─COHP) calculations revealed the crucial role of Mn2+ in lattice stability, as evidenced by the decomposition temperature exceeding 305 °C for CCCH:Sn2+,Mn2+ whereas 210 °C for undoped CCCH matrix. This research provides a comprehensive investigation of the luminescent properties of CCCH:Sn2+,Mn2+ crystal, holding significant promise for practical technological advancements in lighting and anti‐counterfeiting technologies.

Accessing color-tunable afterglows from single conventional chromophore-based polysaccharide films through palette strategy

Achieving multicolor afterglow modulation from single conventional chromophore-based room temperature phosphorescence (RTP) materials is attractive but challenging. Herein, a facile palette strategy based on physical doping of red afterglow-emitted chromophore (N8) into sodium alginate (SA) is proposed to achieve large range of multicolor afterglow modulation for single conventional chromophore-based RTP materials. As well as being a key luminous component in the color palette, SA with cyan afterglow (upon 254 nm UV irradiation) can also activate the red afterglow of N8 via strong hydrogen bond interactions. Through regulating the doping ratios of N8 to SA, cyan to red afterglows have been achieved in the formed amorphous N8/SA films. Significantly, the afterglow of N8/SA also exhibits excitation wavelength- and time-dependent characteristics, which further extend the range and tunability of afterglow color. Besides, the phosphorescence lifetime of N8-based SA films could be further improved by chemically grafting N8 to SA, with a lifetime of 464.9 ms. Considering the excellent multicolor afterglow tunability and hygrothermal responsiveness, these smart SA-based materials demonstrate great application prospects in information encryption, anti-counterfeit ink painting, and 3D afterglow aerogel.

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.

Tunable colors from responsive 2D materials

AbstractOne of the long‐sought‐after goals in responsive material development is to generate and tune colors for advanced and emerging applications such as dynamic displays, light‐emitting diodes, lasers, smart windows, chromic fabrics, high‐security encryption, and visual sensors. Benefiting from the atomically thin nature as well as strong optical interaction, two‐dimensional (2D) materials can serve as color‐generating centers for both chemical pigment colors and physical interference colors in solution, gels, films, and matrix interface systems, to offer new promises for color science and applications. Concerning color tunability, 2D material systems have been demonstrated as one of the ideal responsive materials to achieve the desired goals, including the change of composition, layer thickness, strain, magic angle, and thermally/photically/chemically responsive, magnetically‐responsive, electrically‐responsive, mechanically‐responsive. This makes it an attractive prospect for device applications such as optoelectronics, displays, and nanomedicine. However, to the best of our knowledge, no comprehensive review has been reported specifically on color‐centered aspects of 2D materials. In this review, we highlight experimental approaches and related applications for tuning pigment colors, reflective structural colors, and transmissive interference colors, and we refine the challenges and propose opportunities in future studies for the further development of color science in the 2D material system. Eventually, it is anticipated that this review will serve as a resource and source of inspiration for scientists, as well as open up new avenues for the advancement of color science and related fields in responsive 2D material systems.

A novel optical management layer with flexible color tunability and high transmittance in organic solar cells

The evaluation of colored semi-transparent organic solar cells (ST-OSCs) relies on the power conversion efficiency (PCE) and peak transmittance across the visible light spectrum. However, it is a significant challenge to enhance both parameters simultaneously. In this study, we investigate the impact of different film systems for the Ag electrode on transmittance enhancement using an optical interference formula derived for anti-reflective films. As a result, a novel ZnS/WO3 double-layer anti-reflective film is introduced as an optical management layer. The ZnS/WO3/Ag structure achieves a peak transmittance exceeding 75 % across the visible light spectrum while also offering customizable color attributes. Upon electrical simulation, the power conversion efficiency (PCE) of organic solar cells with 15 nm Ag and 80 nm PM6:Y6 reached to 11.72 %, and an ideal PCE value of 14.53 % is achieved by reducing non-radiative recombination. Through optical simulations, it has been demonstrated that the integration of a ZnS/WO3 double-layer anti-reflective film with organic solar cells enables the generation of OSCs in vibrant purple, blue, cyan, and green hues. Notably, these OSCs exhibit their highest peak transmittance at blue light (452.5 nm), reaching an impressive value of 50.49 %. These remarkable findings not only showcase exceptional performance but also highlight significant potential in applications involving colored OSCs utilizing the new optical management layer composed of ZnS/WO3 double-layer anti-reflective films.

Bicolor Tuning and Hyper-Reflective Color Switching Based on Two Stacked Cholesteric Liquid Crystal Cells with Asymmetric Electrothermal Optical Responses.

We propose a double-cell cholesteric liquid crystal (CLC) device composed of a left-handed (LH) CLC cell with a pair of sheet electrodes and a right-handed (RH) CLC cell with a tri-electrode configuration characterized by a sheet electrode on the top and an interdigitated electrode on the bottom substrates. Bi-reflected color tuning and hyper-reflective color switching are revealed from this cell stack via the electrothermal control of the central wavelengths of the LH- and RH-bandgaps by voltage-induced pseudo-dielectric heating. The two CLCs are thermally sensitive and exhibit overlapped bandgaps in the field-off state with nearly identical temperature dependence, resulting in a hyper-reflective color at 720 nm at 23.4 °C and 380 nm at 29.8 °C. Upon the application of 4 Vrms at 2 MHz across the stacked device to induce pseudo-dielectric heating, two reflective colors can be resolved due to asymmetrical temperature elevations. Accordingly, the difference in wavelength between the two colors increases with increasing voltage through a series cell connection, while maintaining approximately constant via a parallel connection. This study provides a feasible pathway to developing a multifunctional device with electrothermally tunable bi-reflected and hyper-reflective states based on two conventional cell geometries, which is promising for lasers and color-related display applications.

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.

Creating color patterns using optical manipulation and scattering of silicon nanoparticles

The utilization of color patterns has been widely employed in encryption and displays. Printing-based nanostructures are gaining traction in color displays, showcasing remarkable resolution but facing limitations in reconfigurability. Here, we demonstrate a flexible scanning process using optical tweezers to trap silicon nanoparticles (SiNPs) for converting their trajectories into vibrant dynamic color patterns. In this process, the optical potential well stably captures a single SiNP while moving in three-dimensional space at a speed of about 1000 ​μm/s, leading to the display of dynamic color patterns due to persistence of vision (POV). Leveraging the tunable ability provided by Mie resonances within the visible band, the scattering color can be altered simply by adjusting the number of trapped SiNPs, thereby enabling the creation of tunable high-saturation color patterns. This strategy is further explored for flexible design of composite images with potential applications in anti-counterfeiting and dynamic display.

P‐214: TADF/Fluorescent Hybrid WOLED Device with Adjustable Color Temperature

Although the tandem WOLED have the potential of high efficiency and long lifetime, the high voltage of tandem structure usually limits its application inAR/VR products. To achieve low voltage WOLED, it is necessary to develop single structure. Most of the reported single WOLED with the use of TADF materials show a relatively large CIE coordinates. In this work, we use the combination of blue fluorescence and yellow TADF materials with a 1‐2 nm p‐type interlayer material between them. The energy is transferred from blue fluorescence to TADF. And finally, the single WOLED with tunable color temperature was realized. The CIE coordinates can be tuned from the warm white point of (0.313, 0.323) to the cold white point of (0.285, 0.279). The roll‐off of efficiency from 240 nit to 3000 nit is lower than 10%, and the lifetime (LT95) can reach 1300 h at 1000 nit.

Trichromatic color tuning strategy for emission of heterometallic EuIII/TbIII coordination polymers with triazolyl-substituted 4-methyl-phenoxo ligand

Trichromatic color tuning strategy for emission of heterometallic EuIII/TbIII coordination polymers with triazolyl-substituted 4-methyl-phenoxo ligand

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.

Dual-Mode Hydrogels with Structural and Fluorescent Colors toward Multistage Secure Information Encryption.

Constructing an anti-counterfeiting material with non-interference dual optical modes is an effective way to improve information security. However, it remains challenging to achieve multistage secure information encryption due to the limited stimulus responsiveness and color tunability of the current dual-mode materials. Herein, a dual-mode hydrogel with both independently tunable structural and fluorescent colors toward multistage information encryption, is reported. In this hydrogel system, the rigid lamellar structure of poly(dodecylglyceryl itaconate) (pDGI) formed by shear flow-induced self-assembly provides the restricted domains wherein monomers undergo polymerization to form a hydrogel network, producing structural color. The introduction of fluorescent monomer 6-acrylamidopicolinate (6APA) as a complexation site provides the possibility of fluorescent color formation. The hydrogel's angle-dependent structural color can be controlled by adjusting the crosslinking density and water content. Additionally, the fluorescence color can be modulated by adjusting the ratio of lanthanide ions. Information of dual-mode can be displayed separately in different channels and synergistically overlayed to read the ultimate message. Thus, a multistage information encryption system based on this hydrogel is devised through the programed decryption process. This strategy holds tremendous potential as a platform for encrypting and safeguarding valuable and authentic information in the field of anti-counterfeiting.

Omnidirectional color wavelength tuning of stretchable chiral liquid crystal elastomers

Wavelength-tunable structural colors using stimuli-responsive materials, such as chiral liquid crystals (CLCs), have attracted increasing attention owing to their high functionality in various tunable photonic applications. Ideally, on-demand omnidirectional wavelength control is highly desirable from the perspective of wavelength-tuning freedom. However, despite numerous previous research efforts on tunable CLC structural colors, only mono-directional wavelength tuning toward shorter wavelengths has been employed in most studies to date. In this study, we report the ideally desired omnidirectional wavelength control toward longer and shorter wavelengths with significantly improved tunability over a broadband wavelength range. By using areal expanding and contractive strain control of dielectric elastomer actuators (DEAs) with chiral liquid crystal elastomers (CLCEs), simultaneous and omnidirectional structural color-tuning control was achieved. This breakthrough in omnidirectional wavelength control enhances the achievable tuning freedom and versatility, making it applicable to a broad range of high-functional photonic applications.

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.

Strategies to Enhance the Electrochromic Properties of Conjugated Polymers Bearing Pyromellitic Diimide Acceptors.

A series of conjugated polymers bearing thiophene-based donors and pyromellitic diimide (PMDI) acceptor were prepared, and their electrochromic (EC) properties were studied via using fabricated thin-film EC devices. It was observed that structurally regular alternating polymers with fewer (1 and 2) thiophene donors do not exhibit any EC properties while increasing the number of donors eventually led to the emergence of orange-red-to-green colour switching. On this basis, two more random co-polymers containing higher donor-to-acceptor ratios were synthesized to further improve EC switching properties. The two polymers, which bear a PMDI-to-thiophene ratio of ca. 1 : 7 and 1 : 8, revealed orange red-to-blue colour switching and generally improved optical contrasts and switching speeds in both the visible and near infra-red (NIR) region. In addition, the subtle modulation of polymer colour and hue via variation of the number of thiophene donors was evident through colorimetric study. This work therefore demonstrates the potential and possibility of using the PMDI acceptor unit to construct EC-active conjugated polymers, and considerations for future tuning of colour and switching performances.

Fluorescence‐Enabled Colored Bilayer Subambient Radiative Cooling Coatings

AbstractPassive daytime radiative cooling has emerged as a promising green technology for the thermal management of buildings, vehicles, textiles, and electronics. Typically, both high solar reflectance and high thermal emissivity are prerequisites to achieve sufficient daytime cooling. However, colored radiative cooling materials are facing the dilemma of introducing visible light absorption, leading to challenges in balancing cooling and aesthetic demands. Here, three colored bilayer radiative cooling coatings, each comprised of a white base layer and a colored top layer with fluorescence enhancement are fabricated. Three phosphors (Sr2Si5N8:Eu2+, Y3Al5O12:Ce3+, and (Ba,Sr)SiO4:Eu2+) are employed with respective photoluminescence quantum yields (PLQYs) of 81%, 95.8%, and 91.0% as the colored pigment in the top layer. To mitigate the contradiction between coloration and solar reflectance, SiO2 microspheres are introduced into the top layer and utilize their Mie‐resonance‐based multiple scattering to increase the photoluminescent (PL) properties of the phosphors, which jointly boosts the effective solar reflectance (ESR) of the top layer. As a result, the three bilayer coatings exhibit soft colors while achieving subambient cooling with temperature drops of up to 1.5 °C. This fluorescence‐enhancement strategy may pave the way for preparing highly efficient radiative cooling coatings with tunable colors.

Brilliant thermochromic photonic liquid dominated by electrostatic repulsion

It is challenging for traditional methods to generate liquid photonic crystals (LPCs) with brilliant colors and clear self-assembly mechanisms, owing to the major limitations in solvent choice and undesired components. Here, novel LPCs with widely tunable solvents and desired components have been successfully fabricated by non-close-assembling silica particles from silica/ethanol solution into target solvents through alternative centrifugation and sonication. The as-fabricated LPCs exhibit 1) brilliant structural colors from high reflectance (maximal: 91 %) by using solvents with low refractive indexes, much higher than those (20–40 %) of traditional LPCs; 2) tunable color saturation with high precision, difficult for conventional LPCs; and 3) a clearer working mechanism: electrostatic repulsion rather than other interactions majorly dominating the non-close-packing of silica particles in solvents. Additionally, a new type of sensitive thermochromic display unit with thermo-switchable on-off structural colors has been prepared by constructing silica/bi-solvents LPCs. This work not only paves a new way for achieving thermal-responsive LPCs but also offers a new perspective for understanding colloidal assembly.

White-Emitting Gold Nanocluster Assembly with Dynamic Color Tuning.

We report that constructed Au nanoclusters (NCs) can afford amazing white emission synergistically dictated by the Au(0)-dominated core-state fluorescence and Au(I)-governed surface-state phosphorescence, with record-high absolute quantum yields of 42.1% and 53.6% in the aqueous solution and powder state, respectively. Moreover, the dynamic color tuning is achieved in a wide warm-to-cold white-light range (with the correlated color temperature varied from 3426 to 24 973 K) by elaborately manipulating the ratio of Au(0) to Au(I) species and thus the electron transfer rate from staple motif to metal kernel. This study not only exemplifies the successful integration of multiple luminescent centers into metal NCs to accomplish efficient white-light emission but also inspires a feasible pathway toward customizing the optical properties of metal NCs by regulating electron transfer kinetics.