Color Tuning Research Articles

Pure Tunable Emissions from Cesium Manganese Bromide by Monitoring the Crystal Fields Through a Sustainable Approach

AbstractResearch on manganese (Mn) halide perovskite derivatives with tunable emissions and high color purity have gathered a significant amount of attention for display technology. Despite of mesmerizing optical properties, the synthesis of these all‐inorganic Mn halide compounds is followed by complex and toxic processes. Second, a precise control over the synthesis parameters is mandatory to achieve their pure emissions. Therefore, an ecologically sustainable water‐based solution approach is adapted here to tailor the phases and emissions of cesium manganese bromide (Cs‐Mn‐Br) perovskite derivatives. It is observed that a controlled injection of solution stabilizer plays a pivotal role in engineering the intrinsic properties of Mn halide perovskites. This solution stabilizer interacts with the Mn‐ions of those perovskite derivatives influencing their surrounding coordination environment and pure emission from then. A pure green emission with PLQY of 82% is achieved from as prepared Cs3MnBr5, whereas CsMnBr3 showed a red emission with PLQY of ≈20%. Encouraged by these properties phosphor‐driven light emitting diodes (LED) are designed that show a steady electroluminescence intensity. The CIE coordinates of the Cs3MnBr5 and CsMnBr3 LED prototypes are at (0.224, 0.659) and (0.688, 0.316). This study showcases simple, eco‐friendly tactics for developing green and red LED prototypes contributing toward sustainable device design.

Rational Design of Nitride Phosphor-In-Glass with Robust Stability and Photoluminescence Performance.

Phosphor-in-glass represents a promising avenue for merging the luminous efficiency of high-quality phosphor and the thermal stability of a glass matrix. Undoubtedly, the glass matrix system and its preparation are pivotal factors in achieving high stability and preserving the original performance of embedded phosphor particles. In contrast to the well-established commercial Y3Al5O12:Ce3+ oxide phosphor, red nitride phosphor, which plays a critical role in high-quality lighting, exhibits greater structural instability during the high-temperature synthesis of inorganic glasses. A telluride glass with a refractive index (RI = 2.15@615 nm) akin to that of nitride phosphor (∼2.19) has been devised, demonstrating high efficiency in photon utilization. The lower glass-transition temperature plays a crucial role in safeguarding phosphor particles against erosion resulting from exposure to high-temperature melts. Phosphor-in-glass retains 93% of the quantum efficiency observed for pure phosphor. The assembled white light-emitting diodes module has precise color tuning capabilities, achieving an optimal color rendering index of 93.7, a luminous efficacy of 80.4 lm/W, and a correlated color temperature of 5850 K. These outcomes hold potential for advancing the realm of inorganic package and high-quality white light illumination.

Colour tuning in Sm3+ activated and Sm3+/Eu3+ co-activated SrBi4Ti4O15 phosphors for w-LED applications

SrBi4Ti4O15 (SBT) phosphors activated by Sm3+ and co-activated by Eu3+ have been synthesized in the current research using a straightforward solid-state reaction technique. X-ray Diffraction (XRD) confirms the sample's crystallinity. Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), and elemental mapping have been used to analyse the morphology and elemental composition of the synthesized phosphor. Fourier-transform infrared spectroscopy (FTIR) analysis has confirmed the vibrational characteristics of the as prepared phosphor. Photoluminescence studies show increase in luminescence intensity in case of Sm3+/Eu3+ co-activated phosphors as compared with singly doped Eu3+ and Sm3+ activated SBTO phosphors. Colour tunability was also observed from reddish-orange to pure red region when Sm3+ activated phosphors were co-activated with Eu3+ ions. These outcomes demonstrate that SrBi4Ti4O15 phosphors activated or co-activated with Sm3+ and Eu3+ can be deployed in w-LEDs and other display devices applications.

Versatile Aggregation Induced Emissive Molecular Probes Incorporating different Donor/Acceptor groups for Tunable Multiple Color Fluorescence

Excited state intramolecular proton transfer (ESIPT) and aggregation induced emission active multicolour fluorescent probes for bioimaging applications has grown popularly in recent years. Herein, we report a series of different donor/acceptor units (Cl, NO2 and O-CH3) bearing anthracene-salicylaldehyde based fluorescent probes and their antibacterial activity and fluorescence imaging of E. Coli bacteria and zebrafish embryos. All the compounds (ASA1, ASA2, ASA3 and ASA4) synthesized via facile one pot condensation reaction of anthracene hydrazide with Salicylaldehyde, 5-Chlorosalicylaldehyde, 5-Nitrosalicylaldehyde, 5-methoxysalicylaldehyde and characterized using all the possible spectroscopic techniques. The noteworthy tuneable emission wavelength shifts from 471 nm to 625 nm and ESIPT characteristics of the compounds were demonstrated through photophysical experiments and single crystal X-ray diffraction analysis. All the experimental results were completely analysed theoretically on the ground as well as the excited state using density functional theory (DFT) and time dependant density functional theory (TD-DFT) calculations. Compounds ASA1-ASA4 showed fascinating different colour fluorescent (Green, Yellow and Orange) aggregation induced emission features in the THF-H2O mixture. AIE characteristics of ASA1, ASA2, ASA3 and ASA4 were recognized using absorption, emission, fluorescence quantum yield (φ), DLS and SEM analysis. ASA1, ASA2, ASA3 and ASA4 showed excellent antibacterial activity and ROS generation against E. Coli bacteria. Further, owing to the multicolour fluorescent property of the compounds successfully applied for fluorescent imaging in E. Coli bacteria and live zebrafish embryos.

Role of Histidine 310 in Amydetes vivianii firefly luciferase pH and metal sensitivities and improvement of its color tuning properties.

Firefly luciferases emit yellow-green light and are pH-sensitive, changing the bioluminescence color to red in the presence of heavy metals, acidic pH and high temperatures. These pH and metal-sensitivities have been recently harnessed for intracellular pH indication and toxic metal biosensing. However, whereas the structure of the pH sensor and the metal binding site, which consists mainly of two salt bridges that close the active site (E311/R337 and H310/E354), has been identified, the specific role of residue H310 in pH and metal sensing is still under debate. The Amydetes vivianii firefly luciferase has one of the lowest pH sensitivities among the group of pH-sensitive firefly luciferases, displaying high bioluminescent activity and special spectral selectivity for cadmium and mercury, which makes it a promising analytical reagent. Using site-directed mutagenesis, we have investigated in detail the role of residue H310 on pH and metal sensitivity in this luciferase. Negatively charged residues at position 310 increase the pH sensitivity and metal sensitivity; H310G considerably increases the size of the cavity, severely impacting the activity, H310R closes the cavity, and H310F considerably decreases both pH and metal sensitivities. However, no substitution completely abolished pH and metal sensitivities. The results indicate that the presence of negatively charged and basic side chains at position 310 is important for pH sensitivity and metals coordination, but not essential, indicating that the remaining side chains of E311 and E354 may still coordinate some metals in this site. Furthermore, a metal binding site search predicted that H310 mutations decrease the affinity mainly for Zn, Ni and Hg but less for Cd, and revealed the possible existence of additional binding sites for Zn, Ni and Hg.

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.

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.

Three-dimensional core shell InGaN/GaN heterostructure for color tunable emitters on the aspect ratio controlled GaN nanorods

In the pursuit of developing red, green and blue emitters, comprehension of color tunability in relation to the nanostructure properties is imperative. Hence, we present a systematic study for the fabrication of color tunable emitters based on GaN nanorods (NRs) prepared via two-step etching technique. In the essence of tunable emission wavelength, aspect ratio controlled GaN NRs were employed for the growth of core shell heterostructure of InGaN/GaN multiple quantum wells (MQWs) using MOCVD and the impact of aspect ratio regulation on the emission wavelength modulation was studied. To analyze the role of the GaN NRs aspect ratio in facilitating the tunable emission wavelength, we employed metrological as well as optical characterizations. Photoluminescence spectra results established a direct relation of the aspect ratio to the emission profile of the GaN NRs. Furthermore, power-dependent photoluminescence (PL) and cathodoluminescence (CL) studies clarified the source of the emission, providing confirmation of the active region's exclusive growth on non-polar sidewalls and the absence of polarization-induced fields. Tunneling microscope measurements revealed a direct relation of the GaN NRs aspect ratio to the emission wavelength profile. In conclusion, we studied comprehensively the impact of aspect ratio regulation for the tunable emission wavelength.

Color-tunability and energy transfer of a highly thermal-stable BaZnB4O8:Tb3+/Eu3+ phosphor for single-component w-LEDs

A series of Tb3+ single-doped and Tb3+/Eu3+ co-doped BaZnB4O8 samples with color tuning were efficiently synthesized using the solid-state reaction method. The crystal structure, photoluminescence and the energy transfer process (ET) of the samples were systematically studied. The optimal BaZnB4O8:0.08Tb3+ sample shows efficient green emission, then tunable color was achieved by merely introducing a few of Eu3+ ions owing to the highly efficient ET process from Tb3+ to Eu3+ in the BaZnB4O8:0.08Tb3+/yEu3+ samples. The ET efficiency from Tb3+ to Eu3+ of the BaZnB4O8:0.08Tb3+, yEu3+ samples rose from 32.1 % to 51.6 %, simultaneously the luminescent quantum yield improved from 24.7 % to 36.8 %, as the Eu3+ doping concentration increased from 0.125 % to 2 %. Moreover, the Tb3+/Eu3+ co-doped samples exhibited great thermal stability, keeping about 90.2 % (@150 °C) of their original intensity at room temperature. Finally, white light was achieved by a warm w-LEDs fabricated by coating the BaZnB4O8:0.08Tb3+, 0.0025Eu3+ sample on a 365 nm chip. The w-LEDs showed outstanding performance characteristics, with a CCT of 3869 K and a CRI of 89.3. According to the results, Tb3+/Eu3+ co-doped BaZnB4O8 samples have the potential to serve as single-component multicolor-emitting or white-emitting phosphors upon excitation at near-UV wavelength.

Effect of lattice water on the photochromic property/photochromism of a Zn(II)-viologen coordination polymers

Electron transfer is crucial for the rapid response of viologen-based complexes and investigating the factors that affect electron transfer has always been a major challenge. Herein, a new viologen-based complex, formulated as {[Zn5(cbbbc)3(BTC)3(μ1,1-OH)(H2O)5]·22H2O}n, with a three-dimensional framework was successfully designed and synthesized by viologen ligand 1-(3-carboxybenzyl)-4,4′-bipyridinium chloride (Hcbbpy), trimesic acid (H3BTC) and Zn(NO3)2·6H2O. In particular, complex 1 does not exhibit photochromic properties. However, samples of complex 1 heated at 120 and 180 ℃ display tunable colors under UV light irradiation. The experimental results indicate that the compound's light response is less sensitive with higher water content in the lattice. The polarity and hydrogen bonding ability of lattice water in viologen-based complexes can interact with the donor of viologen, leading to a reduction in electron transfer. This study demonstrates the impact of lattice water on electron transfer in viologen-based complexes and offers insights for designing faster response complexes in the future.

Photonic Pigments of Polystyrene-block-Polyvinylpyrrolidone Bottlebrush Block Copolymers via Sustainable Organized Spontaneous Emulsification.

Prior studies on photonic pigments of amphiphilic bottlebrush block copolymers (BBCPs) through an organized spontaneous emulsification (OSE) mechanism have been limited to using polyethylene glycol (PEG) as the hydrophilic side chains and toluene as the organic phase. Herein, a family of polystyrene-block-polyvinylpyrrolidone (PS-b-PVP) BBCPs are synthesized with PVP as the hydrophilic block. Biocompatible and sustainable anisole is employed for dissolving the obtained BBCPs followed by emulsification of the solutions in water. Subsequent evaporation of oil-in-water emulsion droplets triggers the OSE mechanism, producing thermodynamically stable water-in-oil-in-water (w/o/w) multiple emulsions with uniform and closely packed internal droplet arrays through the assembly of the BBCPs at the w/o interface. Upon solidification, the homogeneous porous structures are formed within the photonic microparticles that exhibit visible structural colors. The pore diameter is widely tunable (150∼314 nm) by changing the degree of polymerization of BBCP (69∼110), resulting in tunable colors across the whole visible spectrum. This work demonstrates useful knowledge that OSE can be generally used in the fabrication of ordered porous materials with tunable internal functional groups, not only for photonic applications, but also offers a potential platform for catalysis, sensing, separation, encapsulation, etc.

Colour tuning via energy transfer of K2Ba(MoO4)2: Dy3+/Eu3+ phosphors with thermal-stable property

Colour tuning via energy transfer of K2Ba(MoO4)2: Dy3+/Eu3+ phosphors with thermal-stable property

Effect of concentration of Er3+ on up‐conversion luminescence in NaYF4 containing oxy‐fluoride glass‐ceramics

AbstractThe color of micro‐structured glass can be tuned by adjusting the cross‐relaxation between Er3+ ions through the mechanism of up‐conversion, although the range of color change is very limited. Here, we report the simple and reproducible synthesis of transparent oxy‐fluoride glass‐ceramics co‐doped with Yb3+/Er3+ by melting and secondary heat treatment. By adjusting the doping content of Er3+ ions from 0.2 to 10 mol%, followed by the secondary heat treatment, the intensity of up‐conversion luminescence under 980 nm laser excitation was increased by more than 100 times, and the glass‐ceramics showed an Er3+ doping content‐depended color change of the up‐conversion luminescence from green light to red light. The elemental analysis with TEM–EDS mapping and the measurement of the lifetime of up‐conversion luminescence suggest that changes in the cross‐relaxation between Er3+ ions is the principal mechanism behind the color change of up‐conversion luminescence. As a result, the red emission due to the electronic transition of 4F9/2 is much greater than that of the green emission (4S3/2). Therefore, we present a simple and reproducible strategy to achieve an efficient up‐conversion luminescence from glass‐ceramics with a broad range of color tunability and high color purity.

Thermally stable high carrier mobility nanocomposite infrared photodetector

Quantum dots (QDs) show excellent optical properties, such as a high extinction coefficient, tunable colors, and superior photostability. However, the transport properties of QDs, such as carrier mobility, are quite limited, which hinder optoelectronic applications. On the other hand, carbon nanotubes (CNTs) generally have high carrier mobility and thermal stability with a weak optical response. These features inspire us to couple QDs with CNTs to achieve improved optoelectronics. We take infrared HgTe QDs and multi-walled CNTs as examples. With appropriate coupling between QD and CNT matrices, carrier mobility could reach 34.6–54.1 cm2/Vs in the nanocomposite, a 1000-fold increase compared with the reference. The nanocomposite benefits external quantum efficiency up to 12 500% and detectivity 1012 Jones on the 2500 nm infrared photodetectors. The CNT matrix also helps relaxing thermally generated carriers, improving the photodetector thermal stability. We also demonstrate that the device maintains high detectivity at a high operating temperature.

Fluorine-free synthesis and chromatic properties of V/Pr co-doped zircon ceramic pigment

A fluorine-free route has been developed to fabricate V/Pr co-doped zircon (ZrSiO4) ceramic pigments with Na3VO4 and Pr(NO3)3·6H2O as colourants. The as-prepared pigments were characterized by XRD, Raman, XPS, UV–vis, FE-SEM, TEM and automatic colourimeters. The results show that Na3VO4 can not only act as colourant to produce blue hue, but as mineralizer to accelerate the formation of V/Pr co-doped ZrSiO4 pigment. A colour tuning between blue, green and yellow can be achieved by increasing the mole ratio of Pr/V, and the most intense yellow hue (L* = 74.55, a* = −0.38, b* = 46.82) is obtained at a mole ratio of Pr/V = 0.5. Both Pr4+ and Pr3+ cations are co-existed in the pigments, where Pr4+ contributes to the generation of yellow hue while Pr3+ undermines the yellow hue. The good chromatic ability in glaze at high temperature suggest its potential application in ceramic decoration.

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.

Environmental friendly multifunctional orange pigment for cool coating applications

The present study illustrates the development of an environmentally benign intense orange inorganic pigment, by substituting Si4+ metal ion at the Bi3+ site of Bi4V2O11 via solid-state method. The partial replacement of Si4+, induced a strain in the crystal lattice of the compound, which resulted in a substantial improvement in the visible light reflectance. A reduction in oxygen deficiency in the lattice structure facilitated the colour tuning of the pigment series from brownish red to orange and then on to yellowish orange. The composition Bi3.8Si0.2V2O11+δ exhibited a bright orange hue with colour co-ordinates a* = 39, b* = 34 and L* = 52. Furthermore, NIR solar reflectance of the pigment was 86 %, which is superior than the reported and commercial orange pigments. Compared to commercial pigment coatings, Bi3.8Si0.2V2O11+δ achieved a temperature reduction of 2 °C inside a foam model house. An exceptional corrosion resistance of 1.6 × 1010 Ωcm2, was registered by the pigment loaded epoxy coating with good stability. The corrosion inhibition mechanism of the pigment operates through the hand in hand working of passive Bi-O and Si-O, active FeOOH and vanadate moiety. On the whole, the new multifunctional orange pigment has the potential to be a viable replacement for the toxic commercial pigments in the market.

Understanding and modulating the horizontal orientations and short‐range charge transfer excited states for high‐performance narrowband emitters

AbstractRecently, a novel paradigm of boron‐ and nitrogen‐embedded polycyclic nanographites featuring multiple resonance thermally activated delayed fluorescence (MR‐TADF) has garnered substantial interest due to their extraordinary attributes of efficient narrowband emissions with small full width at half maxima (FWHMs). Despite an array of diverse color tuning strategies, it remains elusive how to effectively manipulate device efficiencies without altering the materials' intrinsic MR‐TADF characteristics. Here, an advanced ‘non‐conjugate fusion’ design methodology was proposed, aimed at dramatically amplifying the horizontal orientations of MR‐TADF emitters while preserving the short‐range charge‐transfer properties. As envisioned, when compared to the classical BCz‐BN mother core, the proof‐of‐concept emitter mICz‐BN achieved an impressively enhanced horizontal dipole ratio (83% vs. 75%) at analogous emission wavelengths (∼486 nm), FWHMs (∼26 nm) and photoluminescence quantum yields (∼93%). Consequently, the external quantum efficiency of the optimized device yielded a performance enhancement of 1.2‐fold (30.5% vs. 25.3%) whilst keeping the spectrum almost unchanged.

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.

Two-Coordinate Thermally Activated Delayed Fluorescence Coinage Metal Complexes: Molecular Design, Photophysical Characters, and Device Application.

Since the emergence of the first green light emission from a fluorescent thin-film organic light emitting diode (OLED) in the mid-1980s, a global consumer market for OLED displays has flourished over the past few decades. This growth can primarily be attributed to the development of noble metal phosphorescent emitters that facilitated remarkable gains in electrical conversion efficiency, a broadened color gamut, and vibrant image quality for OLED displays. Despite these achievements, the limited abundance of noble metals in the Earth's crust has spurred ongoing efforts to discover cost-effective electroluminescent materials. One particularly promising avenue is the exploration of thermally activated delayed fluorescence (TADF), a mechanism with the potential to fully harness excitons in OLEDs. Recently, investigations have unveiled TADF in a series of two-coordinate coinage metal (Cu, Ag, and Au) complexes. These organometallic TADF materials exhibit distinctive behavior in comparison to their organic counterparts. They offer benefits such as tunable emissive colors, short TADF emission lifetimes, high luminescent quantum yields, and reasonable stability. Impressively, both vacuum-deposited and solution-processed OLEDs incorporating these materials have achieved outstanding performance. This review encompasses various facets on two-coordinate TADF coinage metal complexes, including molecular design, photophysical characterizations, elucidation of structure-property relationships, and OLED applications.