Photoluminescence Color Research Articles

Engineering the Strain and Interlayer Excitons of 2D Materials via Lithographically Engraved Hexagonal Boron Nitride.

Strain engineering has quickly emerged as a viable option to modify the electronic, optical, and magnetic properties of 2D materials. However, it remains challenging to arbitrarily control the strain. Here we show that, by creating atomically flat surface nanostructures in hexagonal boron nitride, we achieve an arbitrary on-chip control of both the strain distribution and magnitude on high-quality molybdenum disulfide. The phonon and exciton emissions are shown to vary in accordance with our strain field designs, enabling us to write and draw any photoluminescence color image in a single chip. Moreover, our strain engineering offers a powerful means to significantly and controllably alter the strengths and energies of interlayer excitons at room temperature. This method can be easily extended to other material systems and offers promise for functional excitonic devices.

Photoluminescence enhancement in quantum-dot-polymer films with CO2 micropores through KHCO3 decomposition

Quantum-dot (QDs) polymer composite films, which are key components in recent display applications, require improved photoluminescence (PL) intensity and color conversion efficiency for better display quality and low power consumption. In this study, we developed a novel approach to improve the photoluminescence (PL) of quantum dot (QDs)–polymer nanocomposite films. This was achieved by incorporating CO2 micropores and scattering particles into QD-embedded photopolymerizable polymer films. CO2 micropores were generated by the decomposition of KHCO3 in the film. The CO2 micropores, along with the partially decomposed KHCO3 microparticles, act as a scattering medium that increases the photon absorbance and improves the PL intensity. The effect of KHCO3 annealing temperature on various optical properties is investigated, and it is found that a large number of uniform micropores are created in the film at an optimal temperature, 110 ℃. Compared to an ordinary QD-polymer film, the PL of the QD-hybrid-foamed polymer film increases by 4.2 times. This method is fast and economically efficient, and provides insights into the design of high-performance optoelectronic devices.

Self-reduction induced CaAl12O19:Eu2+/3+: A phosphor with dynamic photoluminescence and photochromism for advanced anti-counterfeiting and encryption

Dynamic photoluminescence and photochromism are two critical technologies applied in advanced anti-counterfeiting and encryption. In this work, an innovative phosphor of CaAl12O19:Eu2+/3+ combining the features of dynamic photoluminescence and photochromism is developed for the first time. After being irradiated by a portable 254 nm ultraviolet lamp, the photoluminescent color of the phosphor can dynamically change from red to magenta in dark field, and the surface color can dynamically alter from white to light brown in bright field. Based on these two appealing features, an application in advanced anti-counterfeiting and encryption is designed which can write, encrypt, and erase information successfully, thus guaranteeing information security. Furthermore, a composite material of CaAl12O19:Eu2+/3+/PDMS is fabricated for application in advanced anti-counterfeiting and encryption in both dark and bright fields, which is difficult to be replicated.

Photoluminescent pyrene-based ionic liquid derived ratiometric organo nanosensor for rapid and selective detection of picric acid

Due to the rising menace of illicit actions and pollution aroused by explosive nitroaromatic compounds (NACs), the growth of an adept sensor for detecting these NACs is highly essential. Herein, in this communication, a photoluminescent IL-assimilated group of uniform materials based on organic salt (GUMBOS) and nano-GUMBOS has been fabricated by integrating pyrene butyrate with a quaternary phosphonium IL (PbIL) via a simple ion exchange process. Neat PbIL shows a bright cyan color photoluminescence under a 365 nm UV lamp irradiation and is employed as photoluminescence security ink and picric acid (PA) detection among the tested NACs. By simple reprecipitation method, we have developed water-suspended crystalline pyrene assimilated nanoparticles, nPbIL, characterized by various analytical techniques. The PbIL-derived water-suspended nanomaterials, nPbIL, display a robust cyan color excimer-like emission, which turns blue (monomeric) due to adding PA over the other related NACs. This ratiometric cyan to blue photoluminesce change is due to the displacement of the anionic pyrene moiety of the nPbIL by the picrate anion. The fabricated organo nanosensor is enormously discerning and responsive towards PA with a detection limit of 0.77 nM and is found to be superior to many available in the literature. Additionally, a fluorogenic paper strip-based test kit experiment has been demonstrated to detect and quantify PA selectively in aqueous solvents amongst the other tested NACs. The present contribution evokes a novel approach to developing different IL-based chemosensors for detecting and quantifying various target analytes.

Zr4+ and Bi3+ codoped Cs2Ag0.3Na0.7InCl6 double perovskite for single-composition white-light emitting phosphors and multimodal optical anti-counterfeiting

Single-composition white-light emitter with excitation-dependent emissions is highly desired for phosphor-converted white-light emitting diodes (WLEDs) and optical anti-counterfeiting, in terms of the optical self-absorption and degeneration induced by the different components. However, the rational regulation of excitation-dependent multi-emissions in single perovskite materials is still a grand challenge. Herein, Bi3+ and Zr4+ codoped Cs2Ag0.3Na0.7InCl6 double perovskite microcrystals (DPMCs) were reported for single-composition white-light emitting phosphors and multimodal optical anti-counterfeiting. As a result, the photoluminescent quantum yield (PL QY) and color rendering index (CRI) were recorded up to 80.3% and 95.8, respectively. Specifically, under ultraviolet (UV) excitation at 365 nm, the Zr4+-doped DPMCs exhibited distinct emission profiles with single broad band centered at ∼570 nm for various Zr4+ doping concentrations, which could be attributed to the self-trapped exciton (STE) emission of the host. While the DPMCs show dual emission bands centered at ∼470 and ∼570 nm excited at 254 nm, which originates from the [ZrCl6]2- octahedral and STE, respectively, and their integral PL intensity ratio can be gradually adjusted by the content of Zr4+. The broad multicolor emissions with color kinetic features of the single-composition DPMCs offer exciting opportunities for constructing WLEDs and multimodal optical anti-counterfeiting.

21‐3: Quantum Rod Color Filters with High Ambient Contrast Ratio

Applying quantum dot (QDs)‐based photoluminescent color filter arrays to mono‐color OLED displays and liquid crystal displays is considered a promising method to broaden the color gamut and boost the brightness and efficiency of the display. However, the ambient light could excite the semiconductor QDs and QRs, decreasing the display ambient contrast ratio. Adding a traditional absorptive CF array has limited functions in solving this problem due to the broadband transmission band of pigments. With a larger Stokes shift, QRs are more suitable for suppressing photoluminescent reflection. In this article, we simulate the ambient contrast ratio of a QD/QR‐OLED display, considering the parameters of backlight, the Stokes shift, the absorption strength, and spectral properties of QRs, QDs, and absorptive CFs, our discussion provides insight for optimization of the display ambient contrast ratio.

72‐2: Invited Paper: Color‐Conversion Liquid Crystal Display with In‐Cell Polarizer

An approach to developing a thin‐film polarizer with high polarization efficiency in liquid crystal cells is presented. The in‐cell polarizer facilitates the realization of novel color‐conversion liquid crystal displays, where advanced quantum color‐converters are used as photoluminescent color filter arrays. We experimentally demonstrated using azo‐dye‐based embedded polarizers for color‐conversion liquid crystal displays for the first time. We systematically designed the device structure and fabrication process. The display is color parallax free and can be driven at regular conditions with good contrast.

A PET and ESIPT-communicated ratiometric, turn-on chromo-fluorogenic sensor for rapid and sensitive detection of sarin gas mimic, diethylchlorophosphate

Fast and precise identification of toxic G-series nerve agents in the solution and vapor phase is urgently needed to save human beings from unwanted wars and terrorist attacks, which is challenging to execute practically. In this article, we have designed and synthesized a sensitive and selective phthalimide-based chromo-fluorogenic sensor, DHAI, by a simple condensation process that shows ratiometric and turns on chromo-fluorogenic behavior towards Sarin gas mimic diethylchlorophosphate (DCP) in liquid and vapor phases, respectively. A colorimetric change, from yellow to colorless, is observed in the DHAI solution due to the introduction of DCP in daylight. A remarkable cyan color photoluminescence enhancement is noticed in the presence of DCP in the DHAI solution, which is observable to the naked under a portable 365nm UV lamp. The mechanistic aspects of the detection of DCP by employing DHAI have been revealed by time-resolved photoluminescence decay analysis and 1H NMR titration investigation. Our probe DHAI exhibits linear photoluminescence enhancement from 0 to 500μM with a detection limit of nanomolar range from non-aqueous to semi-aqueous media. For practical utility, a DHAI-stained test kit employing Whatman-41 filter paper has been fabricated and used as a portable and displayable photonic device for on-site detection of Sarin gas surrogate, DCP. Also, a dip-stick experiment has been demonstrated to identify the vapor of Sarin gas mimics DCP colorimetrically and fluorometrically. The concentrations of DCP in various water samples have been evaluated with the help of a standard fluorescence curve for real sample analysis.

Crystal-Liquid-Glass Transition and Near-Unity Photoluminescence Quantum Yield in Low Melting Point Hybrid Metal Halides.

Hybrid metal halides (HMHs) are a class of materials that combine extraordinary photophysical properties and excellent processability. Their chemical variability allows for the solid-liquid transition toward melt-processable HMHs. Herein, we report the design and synthesis of zero-dimensional HMHs [M(DMSO)6][SbCl6], where the isolated octahedra of [M(DMSO)6]3+ and [SbCl6]3- are alternatively aligned in the crystal structure. The luminescent center of [SbCl6]3- enables the photogeneration of self-trapped excitons, resulting in broadband photoluminescence with a large Stokes shift and a nearly 100% quantum yield. Meanwhile, the release of DMSO ligands from [M(DMSO)6]3+ is controlled by the M-O coordination and thus a low melting point of ∼90 °C is achieved for HMHs. Interestingly, the glass phase is obtained by melt quenching, with a sharp change in photoluminescence colors compared to the crystal phase of melt-processable HMHs. The robust crystal-liquid-glass transition opens a new avenue to tailoring structural disorder and optoelectronic performance in organic-inorganic materials.

Ultraviolet-photoluminescence and trace element analyses in Ga-rich sphalerite from the Djebel Gustar Zn-Pb deposit, Algeria

The Djebel Gustar Zn-Pb deposit in northeastern Algeria is one of many carbonate-hosted base metal deposits in the Atlas metallogenic province of North Africa. The sphalerite in this deposit occurs in five distinct types that differ in texture, mineral assemblage, chemical composition, and UV photoluminescence signature. Detailed investigation of trace elements by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) showed that the sphalerite is significantly enriched in the critical metal Ga. The trace element concentrations of the different sphalerite types correlated well with their photoluminescence color; with Mn2+ (orange-yellow), Cu+ (green), and Ga3+ (red) being the dominant activators. We suggest that the Ga enrichment in the Djebel Gustar deposit is the result of formation conditions that include the mixing of a Cl-rich fluid carrying mainly Zn and Pb with a more reduced and Cl-poor fluid containing considerable organic matter and/or calcite with adsorbed Ga(OH)3. This Ga was subsequently incorporated into sphalerite, rather than forming a stoichiometric Ga phase. Furthermore, our study demonstrates that UV photoluminescence of low Fe sphalerite has the potential to become a simple and affordable tool for preliminary characterization of sphalerite ores in mining and exploration with respect to critical elements such as Ga.

Development of Donor-π-Acceptor-Type Fluorinated Tolanes as Compact Condensed Phase Luminophores and Applications in Photoluminescent Liquid-Crystalline Molecules.

Fluorinated tolanes, produced by introducing fluorine atoms into one of the aromatic rings of tolane, emitted almost no fluorescence in a solution state, but the fluorescence intensity increased dramatically in the crystalline state because of intermolecular H⋅⋅⋅F hydrogen bonds. The photoluminescent (PL) colors depend on the molecular orbitals, dipole moments, and molecular aggregated structures can be varied by controlling terminal substituents along the major molecular axis. The introduction of a long alkoxy or semifluoroalkoxy unit as a flexible chain into the terminal positions along the major molecular axis induced the formation of a liquid-crystalline (LC) phase; fluorinated tolanes act both as luminophores and as mesogens, leading to the molecular design of new photoluminescent LC molecules (PLLCs). The results also indicated that a fluorinated tolane dimer, which consists of two fluorinated tolanes linked by a flexible alkylene spacer, also becomes a novel PLLC.

Phthalimide‐Based Off‐On‐Off Fluorosensor for Cascade Detection of Cyanide Ions and Picric Acid

AbstractNovel methods that can be utilized to identify and detect harmful environmental pollutants still need to be proposed. This article describes the effective design and development of a turn‐on photoluminescence probe, T1 [(E)‐5‐((2‐hydroxybenzylidene) amino) isoindoline‐1, 3‐dione], which is selective and sensitive towards CN− ions having detection limit nM to μM range. When exposed to CN− ions, Probe T1 displays a strong fluorescence response under a 365 nm UV light irradiation with a noticeable low to high intense cyan color photoluminescence visible to the naked eye. For the practical utility of the present probe T1, a paper strips‐based test kit experiment has been demonstrated as a portable and displayable photonic device for on‐site detection of CN− ions. Furthermore, the T1‐CN− adduct has been applied for detecting explosive nitroaromatic compounds, especially PA, based on the photoluminescence quenching mechanism. Using CN− ions, and PA as chemically encoded inputs and corresponding optical output, a molecular logic gate has been constructed. Further, probe T1 has been employed as a bio‐analytical tool to map intercellular CN− ions in live cells. This study invokes a novel approach for designing and developing efficient and selective sensors employing well‐known fluorescent probes as signaling units with prior photophysical knowledge.

Divulging the Potential of Sodium Carbide Thin Film for Semiconductor Applications

The work reported in this article is an attempt to introduce the least explored sodium carbide as a thin film and to explore its semiconducting behavior. The sodium carbide thin film deposited by the radio frequency sputtering technique is subjected to morphology, structure, and spectroscopic characterizations. The floral petal‐like morphology, understood from the field‐emission scanning electron microscopy and atomic force microscopy images, helps in enhancing interaction with the radiation that is revealed through the UV–visible absorption spectrum. X‐ray diffraction, photoelectron and Raman spectroscopic analyses confirm that the film is sodium carbide. The optical emission behavior of the sodium carbide thin film in the blue region is unveiled through the photoluminescence spectrum, power spectrum, color purity, and chromaticity diagram. Employing the refractive index and extinction coefficient values from the specular reflectance data, optical and electrical conductivities, nonlinear refractive index, linear and nonlinear optical susceptibility, dissipation factor, and surface and volume energy loss functions and their wavelength dependence due to interfacial polarization are investigated. The transfer matrix method is used to understand the spatial variation of the induced electric field and optical current density.

Thermally Activated Delayed Fluorescence and Room‐Temperature Phosphorescence in Sulfidoazatriangulene‐Based Materials and their S‐oxides

AbstractStructural constraint is an emerging strategy for improving the photoluminescence quantum yield, molar absorptivity, and color purity of luminescent materials. In this report, emitters displaying thermally activated delayed fluorescence (TADF) are achieved for the first time using the planarized donor sulfidotetramethyazatriangulene (SMAT). Compared to non‐planarized phenothiazine (PTZ) donors, the enhanced rigidity of SMAT contributes to improved color purity and photoluminescence quantum yield, with up to 90% quantum yield observed for donor–acceptor compounds in toluene solution. Planarized SMAT‐based emitters also offer up to tenfold enhancement in two‐photon absorption cross‐section compared to analogous PTZ‐based materials. Oxidation of sulfur‐containing donors to sulfoxide and sulfone derivatives is demonstrated as a simple and generalizable means of tuning the electron‐donating ability of sulfur‐containing moieties. SMAT‐TRZ and SOMAT‐TRZ both exhibit TADF, with green and blue emission, respectively, while SO2MAT‐TRZ displays blue room temperature phosphorescence. Overall, this work demonstrates that SMAT and its S‐oxides can be used to design high‐performance luminescent materials with emergent properties such as TADF or room‐temperature phosphorescence.

Photophysical Properties of Bright Luminescent Polyethyleneimine@Carbon Nanodots and Their Application in White Light-Emitting Diodes

Highly fluorescent carbon nanodots (CNDs) have broad application prospects in optoelectronics, energy, biological imaging, and other fields because of their good solubility in water, adjustable photoluminescence (PL), low toxicity, good biocompatibility, and stable chemical properties. In this paper, polyethyleneimine@CNDs (PEI@CNDs) with unique excitation- and concentration-dependent PL properties were synthesized by a one-pot hydrothermal approach. The morphology, structure, surface chemistry, photophysical properties, and stability of the PEI@CNDs were well probed. The PEI@CNDs solution at low concentration displayed blue PL with a quantum yield of 50.6%. As the concentrations of the PEI@CNDs increase, the PL colors changed from blue, cyan, and green, to greenish-yellow. At low concentration, the excitation-independent and excitation-dependent PL property is mainly caused by carbon core and surface state emission. However, at higher concentration, the quenched blue emission and enhanced green emission were found. This is mainly attributed to the aggregate-related inner filter effect, electron transfer, and surface states. Mixing 10.0 mg/mL of PEI@CNDs with polyvinyl alcohol can be used to construct composite films, which were combined with the blue light-emitting diode to construct white light-emitting diodes with white and warm white emissions.

Multi-stimuli, color switchable emitter by solvent induced polymorph synthesis

Polymorphism has drawn great attention in tuning organic solid-state luminescent materials by alteration of molecular packing structure and has considerable potential application in optoelectronic devices and fluorescence sensors. Herein, two polymorphs based on dicyanodistyrylbenzene (DCS) compound were obtained by solvent induced synthesis. We have comprehensively investigated photophysical properties (such as photoluminescence colors, lifetime and PL quantum yield) of the two polymorphs, blue one αDCFDCS (Aqua) and green one αDCFDCS (Green). The single crystal structure analysis and XRD powder pattern shows that there is a slightly packing dislocation in a-axis account for the difference between the two phases. Mechanical grinding can lead to an alternation in photoluminescence color from blue to green. The differential thermal analysis (DTA) measurement discloses αDCFDCS (Aqua) is the metastable state of the compound. Both of two polymorphs show thermochromic and can be reversibly switched upon heating and cooling, which is attributing to the crystal cell expansion with the temperature increasing revealed by in situ XRD. Moreover, fuming with NH3 also causes the color change via Lewis acid base reaction. Upon heating or being exposed to HCl, it will return to the original state. The results of the polymorphism not only provide an insight into molecular packing and emission properties, but also pave the way for understanding the solid luminescence change by the multi-stimuli response.

An Oligomer Approach for Blue Thermally Activated Delayed Fluorescent Emitters Based on Twisted Donor-Acceptor Units.

The development of efficient blue donor-acceptor thermally activated delayed fluorescence (TADF) emitters remains a challenge. To enhance the efficiency of TADF-related processes of the emitter, we targeted a molecular design that would introduce a large number of intermediate triplet states between the lowest energy excited triplet (T1) and singlet (S1) excited states. Here, we introduce an oligomer approach using repetitive donor-acceptor units to gradually increase the number of quasi-degenerate states. In our design, benzonitrile (BN) moieties were selected as acceptors that are connected together via the amine donors, acting as bridges to adjacent BN acceptors. To preserve the photoluminescence emission wavelength across the series, we employed a design based on an ortho substitution pattern of the donors about the BN acceptor that induces a highly twisted conformation of the emitters, limiting the conjugation. Via a systematic photophysical study, we show that increasing the oligomer size allows for enhancement of the intersystem crossing and reverse intersystem crossing rates. We attribute the increasing intersystem crossing rate to the increasing number of intermediate triplet states along the series, confirmed by the time-dependent density functional theory. Overall, we report an approach to enhance the efficiency of TADF-related processes without changing the blue photoluminescence color.

S-Tetrazine derivative exhibiting unprecedented polymorphism-dependent emission properties

The first example of a tetrazine derivative exhibiting emission color-tunable crystals upon external stimuli such as heat and an organic solvent is described. Bis(4-methylphenoxy)tetrazine (1) forms several crystalline phases by heating and cooling processes accompanying unprecedented photoluminescence color transitions including green, yellow, red, and traditional orange colors. These thermoresponsive polymorphisms and colors could be also reversibly recovered to their original state by solvent vapor annealing. The formation of mild excimer-like species and energy state transitions (much-stabilized ground state than the S1 state) presumably contributed to the unique bathochromic and hypsochromic shifts, respectively. In addition, a novel mechanical feature from 1- the formation of flexible crystals- was achieved, which plausibly originated from the unique T-shape arrangement of the tetrazine rings and the phenyl rings observed in the molecular packing.

Effective Thermal Diffusion of Eu(III) and F Ions into Hydroxyapatite Nanoparticles by Citric Acid Coordinative Mediation

We synthesized citric acid (Cit)-coordinated Eu3+ and F– codoped hydroxyapatite (Cit/Eu:HA-F) nanoparticles (NPs) and investigated their ion diffusion processes based on photoluminescence (PL) properties at the near-surfaces with thermal treatment. At 85 °C, the Cit coordination layer effectively suppressed the nonradiative deactivation of HA NP surfaces in the PL process, and the quantum yield (ηint) of Eu3+ ions reached a maximum value of ca. 33%, indicating the highest PL efficiency in the HA system. At 250 °C, Cit was decomposed into aconitic acid with a high optical absorption coefficient and reducing ability, so that the ηint of the Eu ions in the NPs were minimized and the partial Eu3+ ions were resultantly reduced to Eu2+ ions. At around 350 °C, the Eu ions were partially diffused from Ca(I) into Ca(II) sites. At 550 °C, the proportion of Eu ions in Ca(II) sites dramatically reached up to ca. 31%, and the F– ions simultaneously diffused into the HA structures by substituting for the OH sites. Therefore, it was elucidated that the Cit molecules coordinated to the Eu and F– codoped HA surfaces achieved higher ηint and promoted the diffusion of various ions into the HA structures with thermal treatment and resultantly controlled the existence ratio of the Eu3+ and Eu2+ ions at the near surfaces, which could be expected to control the PL color by the Cit coordinative mediation technique and realize the creation of cell-labeling luminescent nanomaterials in biomedical fields.

Development of Uniform Polydimethylsiloxane Arrays through Inkjet Printing

The inkjet printing method is a promising method to deposit polymer and functional nanoparticles at the microscale. It can be applied in the fabrication of multicolor polymer light emitting diodes (polyLEDs), polymer base electronics, multicolor color conversion layers, and quantum dot light emitting diodes (QLEDs). One of the main challenges is to print high-resolution polymer dots from dilute polymer solution. In addition, the quality of printed multicolor polyLEDs, QLEDs and multicolor color conversion layers is currently limited by non-uniformity of the printed dots. In this paper, polydimethylsiloxane (PDMS) is selected as the functional polymer, due to its high transparency, good reflective index value, inflammable and flexible properties. The optimal ink to form a uniform PDMS dot array is presented in this paper. Both the solvent and PDMS were tuned to form the uniform PDMS dot array. The uniform PDMS dot array was printed with a diameter of around 50 µm, and the array of closely spaced green quantum dots (QDs) mixed with PDMS ink was also printed on the substrate uniformly. While the green QD-PDMS film was printed at a resolution of 1693 dpi, the uniformity was evaluated using the photoluminescence (PL) spectrum and color coordinate value.