Green Light-emitting Materials Research Articles

Tackling toxicity and stability using eco-friendly metal-halide ion substituted perovskite nanocrystals for advanced display color conversion

In recent years organic–inorganic hybrid halide perovskites nanocrystals have made a remarkable impact in display color converting layer application. However, lead toxicity and stability issues always pose arduous challenges. In this regard, the incorporation of a suitable metal ion to reduce toxicity and enhance stability is a widely tested method. In this study, we used a simple ligand-assisted reprecipitation (LARP) technique to simultaneously introduce metal ion and halide ion substitution by synthesizing MAPb1-xZnxBr3-2xCl2x nanocrystals (NCs). Being eco-friendly with a smaller ionic radius than lead ion, zinc metal ion was chosen as a substitute. With the variation of Zn2+ concentration, the highest quantum yield of 95 % was recorded with an emission width of 21 nm. Temperature-dependent photoluminescence (PL) studies revealed the higher optical phonon-exciton interaction after Zn2+ incorporation leading to radiative transition in NCs. Variation of PL peak energy with temperature revealed the reduced thermal chromaticity of Zn2+ incorporated NCs making them suitable for display application. Further, these NCs maintained a stable cubic structure and luminescence up to 150 °C, indicating higher thermal stability. The MAPb0.9Zn0.1Br2.8Cl0.2 (x = 0.1 or 10 mol%) NCs embedded in PMMA (poly (methyl methacrylate) polymer matrix coated LED emits narrow width, green light with color coordinate (0.15, 0.79), which is closer to green coordinate (0.17, 0.79) in Rec.2020. This helps to reproduce close to 97 % color gamut of Rec.2020. This research paves the way for finding less toxic and stable green light-emitting materials instead of cadmium-based molecules.

Potential usage of cesium manganese halide for multi-functional optoelectronic devices: Display & photodetector application

The composition of manganese, which exhibits tetrahedral coordination with halogen ligands, makes it excellent for use in green light-emitting materials. In particular, zero-dimensional Cs3MnBr5 material has continuously been researched as a lead-free all-inorganic light emitting material. It has excellent optical properties such as center wavelength and full width at half maximum. The most recent studies on Cs3MnBr5 have synthesized it using a bottom-up method. However, the problem of notably poor particle uniformity or efficiency remains. The aim of this study was to develop sub-micron-sized Cs3MnBr5 particles with octahedron or truncated shapes by modifying the existing hot-injection synthesis method. Sub-micron Cs3MnBr5 particles showed 60% photoluminescence quantum yield (PLQY) under blue light excitation and absorbed light in the entire visible light region, including the absorption edge by PLE. Therefore, we explored existing research on light conversion films for LED & micro-LED and photodetector applications with a focus on optical properties of Cs3MnBr5 particles.

Blue Organic Light Emitting Diode Materials based on Different Light-emitting Groups

Abstract: Organic light emitting diode (OLED) is a device that uses organic semiconductor materials to emit light under the action of an electric field. Compared with traditional luminescent materials, they have the advantages of good softness, low-temperature resistance, wider field of vision and low energy consumption, and have been widely used in the field of display and lighting in recent years. In addition, compared with red and green light-emitting materials, the maximum external quantum efficiency of blue-light materials-based devices is high, but the CIE coordinate performance is poor and the blue emission is difficult to achieve high efficiency and high color purity at the same time. Researchers continue to design new molecular structures in order to synthesize new high-efficiency blue light materials. It is found that different molecular structures have different effects on the performance of OLED devices. In the design and synthesis of blue-light materials, various light-emitting groups are often used to regulate the stability, singlet-third-line state of the target molecule energy level difference, excited state lifetime, aggregation state structure, electricity luminescent color and its OLED performance, etc. The introduction of different lightemitting groups into the blue light material greatly improves the performance of the material. This paper mainly reviews the research status of blue organic electroluminescent materials in the past five years from different molecular structures, further discusses the photoelectric properties of each compound and the properties of devices based on this material, and briefly analyzes the advantages of molecular design and device production. And finally discusses the improvement methods of blue OLED light-emitting materials in order to provide a reference for future research.

Augmentation of photophysical features and Judd-Ofelt analysis of extensively green glowing terbium (III) complexes with nitrogen donor ancillary ligands.

Six green glowing terbium (III) complexes were fabricated via grinding method utilizing a prime organic ligand (L) and nitrogen donor ancillary ligands. Characterization of synthesized complexes was accomplished through various spectroscopic techniques. The significant thermal stability was determined by thermogravimetric analysis while the energy bandgap and Urbach energy were investigated through diffused reflectance spectra of these complexes. The peak observed at 548nm in emission spectra is responsible for the virescent color of these complexes. Color purity, decay time, quantum yield, and emission intensities of ternary complexes were significantly improved as compared to binary ones due to the synergistic effect of ancillary ligands. Judd-Ofelt parameters were determined by the NIR absorption spectrum, which claims the asymmetric environment around the terbium (III) ion. CCT values advocate the applicability of these complexes in green light-emitting materials as a cool light source. The biological assignments reveal the significance of these complexes as potent antioxidants and antimicrobial agents. The energy transfer process highlights the enhancement of luminescence in these complexes via the synergic effect of ligands. Our investigation portrays that these complexes can be employed in laser technology, display devices, semiconductors, biological fields, and optoelectronic devices.

Optical characterization and emission enhancement property of Ag nanomesh structure fabricated by nanosphere lithography

A metal nanomesh structure with regularly arranged nanosized holes has a light transmission property at a certain wavelength region and good conductivity; therefore, it can be applied to the wavelength-selective electrode of optical devices such as organic light-emitting diodes (OLEDs) and solar cells. In this study, Ag nanomesh structures with hole arrays of different sizes and periods were fabricated, and their electrical and optical properties were evaluated. Alq3, a green light-emitting material for OLEDs, was deposited on the fabricated Ag nanomesh, and its transmission, scattering, and photoluminescence (PL) spectra were investigated. The PL intensity of Alq3 was approximately four times higher than that without the Ag nanomesh. Time-resolved PL measurements showed the presence of a short-lived component in all samples with Ag nanomesh, indicating plasmonic emission enhancement. These results indicate that Ag nanomeshes can be applied as plasmonic electrodes in optical devices.

Operando direct observation of spin-states and charge-trappings of blue light-emitting-diode materials in thin-film devices

Spin-states and charge-trappings in blue organic light-emitting diodes (OLEDs) are important issues for developing high-device-performance application such as full-color displays and white illumination. However, they have not yet been completely clarified because of the lack of a study from a microscopic viewpoint. Here, we report operando electron spin resonance (ESR) spectroscopy to investigate the spin-states and charge-trappings in organic semiconductor materials used for blue OLEDs such as a blue light-emitting material 1-bis(2-naphthyl)anthracene (ADN) using metal–insulator–semiconductor (MIS) diodes, hole or electron only devices, and blue OLEDs from the microscopic viewpoint. We have clarified spin-states of electrically accumulated holes and electrons and their charge-trappings in the MIS diodes at the molecular level by directly observing their electrically-induced ESR signals; the spin-states are well reproduced by density functional theory. In contrast to a green light-emitting material, the ADN radical anions largely accumulate in the film, which will cause the large degradation of the molecule and devices. The result will give deeper understanding of blue OLEDs and be useful for developing high-performance and durable devices.

Evaluation of structural, Hirshfeld surface and density functional theory of novel NLO thienyl chalcone single crystal

A novel NLO-active chalcone derivative (E)-1-(5-chlorothiophene-2-yl)-3-(4-dimethylamino) phenyl) prop-2-en-1-one has been synthesized by adopting Claisen–Schmidt condensation reaction method. Using DMF as solvent, single crystals of the compound were grown by solution growth technique. The grown crystals are of diamond-shaped dark red colour in nature, and these crystals are characterized using different experimental methods. NMR and LC–MS spectral methods are used to confirm the molecular structure of the synthesized compound. The observed fluorescence spectrum clearly signifies that the newly grown crystal could be utilized as a new green light-emitting material. The molecular 3-dimensional hirshfeld surface and the corresponding 2-dimensional finger print plot representation quantifying the percentage contribution of each individual atom present in the compound were studied. From the density functional theory, the values of HOMO, LUMO and their energy gap were determined. The values of global chemical reactivity descriptors such as chemical hardness (η), global softness (σ), electrophilicity (ω), ionization potential (I) and chemical potential (μ) have been calculated. The molecular electrostatic potential map identifies the potential sites for electrophilic and nucleophilic attack in the molecule. The NLO parameters such as molecular polarizability (α), dipole moment (μ) and first-order hyperpolarizability (β) were determined using density functional theory.

Synthesis of Ir(III) Complexes Containing Meta-Carbonylated Phenylpyridine Ligand for Phosphorescent Organic Light-Emitting Diodes

The photophysical characteristics of phosphorescent Ir(III) complexes 1–3 were investigated to determine their suitability as candidates for green light-emitting materials for OLEDs. To evaluate the EL properties of using these compounds as dopant in the emitting layer, multilayered devices were designed as green-light-emitting device having the following configuration: ITO/NPB (30 nm)/Ir(III) complexe 1 (5 and 10 wt.%) doped in CBP (30 nm)/BCP (10 nm)/Alq3 (40 nm)/Liq/Al were fabricated. An OLED device employing 1 as a dopant exhibits the performance with a maximum luminance of 46000 cd/m2 at 14.0 V. The luminous efficiency, power efficiency were 17.3 cd/A, 6.97 lm/W at 20 mA/cm2, respectively. Also, this device shows green emission with CIE coordinates of (0.247, 0.594) at 10.0 V.

Syntheses of a Green Organic Phosphorescence Materials and Studies on their Photoluminescent Properties

Using the second o-nitro aniline and benzoyl chloride as the initial raw materials, a green light-emitting materials (pbi)2Ir (acac)2 was produced utilizing a new designed synthesis plan. The complex’s structures were characterized by IR, MS, and the differential thermal analysis. The optical Luminescence Properties of the complex was studied by the fluorescence spectrometry analysis. The melt point of the product is 343°C which showed that it had thermal stability.. The fluorescence spectrometry analysis experimental results show that the Excitation and emission peaks of the organic Iridium (Ⅲ) complexes got were respectively 470.6nm and 526.21nm which showed that it belong to green high-brightness light-emitting materials. The oxidation of the intermediate products exposed in air which could cause the quality of product instability was avoided in the new synthesis plan improved.

Significant enhancement of blue emission and electrical conductivity of N-doped graphene

Nitrogen (N)-doped graphene with different atomic percentages (2.3–4.7 at%) of N has been synthesized by thermal annealing of reduced graphene oxide (RGO) in ammonia gas for different times. The effects of annealing time on the structure, electrical and optical properties of N-doped graphene have been systematically investigated by using various analytical techniques. XPS, FTIR, Raman, and XRD studies show that there is a gradual structural change in N-doped graphene sheets with increasing annealing time, resulting from the increase of carbon and simultaneous decrease of oxygen and N contents. High resolution N1s spectra reveal that the pyridine-N and pyrrolic-N contents decrease with increasing annealing time, whereas the amount of quaternary-N increases. Importantly, it has been found that the annealing time caused significant changes in both the electrical and the optical properties of N-doped graphene. The electrical resistance of N-doped graphene is greatly reduced compared to that of GO and RGO, and found to further decrease with increasing annealing time, possibly due to the increase of sp2 carbon networks and decrease of oxygen content as well as defects associated with the incorporation of N. The room-temperature photoluminescence (PL) properties of graphene oxide (GO), RGO and N-doped graphene were systematically studied with regard to the annealing time. The results showed that the PL spectrum of GO exhibits a peak emission maximum at around 700 nm, while that of RGO is found to be strongly blue-shifted with two distinct emission peaks: green emission at 485–500 nm and blue emission at 420–428 nm. For N-doped graphene samples, the blue emission intensity could significantly be enhanced by controlling the annealing time, which leads to a promising blue and green light-emitting material with controllable optical properties.

Effect of one ligand substitution on charge transfer and optical properties in mer-Alq3: a theoretical study

In tris(8-hydroxyquinolinato)aluminum (mer-Alq3) position for substitution plays an important role. We explain the push–pull effect on the charge transfer and optical properties, if only one of the ligand among three ligands of meridianal isomer of mer-Alq3 has been substituted. To check this effect, we substituted A-ligand with electron-donating group at position 4 and electron-withdrawing group at position 6. We designed 4-methyl-6-chloro-(8-hydroxyquino)bis(8-hydroxyquinolinato)aluminum (1), 4-methyl-6-cyano-(8-hydroxyquino)bis(8-hydroxyquinolinato)aluminum (2), 4-amino-6-chloro-(8-hydroxyquino)bis(8-hydroxyquinolinato)aluminum (3), and 4-amino-6-cyano-(8-hydroxyquino)bis(8-hydroxyquinolinato)aluminum (4) derivatives of mer-Alq3. All the studied derivatives in the ground (S0) and first excited (S1) states have been optimized at the B3LYP/6-31G* and CIS/6-31G* level of theory, respectively. We have designed green light-emitting materials like mer-Alq3 and blue light-emitting materials. These derivatives are good candidates for comparable/better charge carrier mobility as mer-Alq3.

High-brightness, high-color-purity, white organic light-emitting diodes featuring multiple emission layers

We have developed high-brightness, high-color-purity, white organic light-emitting diodes featuring three emission layers: (i) the green light-emitting material 1,3,5-tris(1-pyrenyl)benzene (TPB3), (ii) the host material 1,4-bis(2,2-diphenylvinyl)biphenyl (DPVBi) doped with the blue dye di(4-fluorophenyl)amino-di(styryl)biphenyl (DSB), and (iii) tris(8-hydroxyquinoline)aluminum (Alq3) doped with the red dye 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB). A device having the configuration indium tin oxide (1300 Å)/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (500 Å)/TPB3 (200 Å)/DPVBi: 2 wt % DSB (150 Å)/Alq3: 2 wt % DCJTB (150 Å)/Alq3 (350 Å)/LiF (8 Å)/Al (2000 Å) exhibited a white emission with a maximum luminance at 15 V of 55 800 cd/m2, a maximum current efficiency of 4.06 cd/A at 13 V, a maximum power efficiency of 2.24 lm/W at 5 V, and a maximum external quantum efficiency of 2.45% at 5 V. The Commission Internationale de l’Eclairage coordinates of (0.33, 0.32) changed only slightly upon varying the potential from 9 to 13 V. We attribute the high brightness and color purity of the emitted white light to the high electroluminescence of the hosts and dopants, the relatively high efficiency of the energy transfer from the hosts to the dopants, and the high control over the thicknesses and dopant concentrations of the red-, green-, and blue-emitting layers, resulting in suitable numbers of partial excitons being generated in each of those three layers.

Electrodeposition of high quality and freestanding poly(9,9-dioctylfluorene-co-thiophene) films with good fluorescence properties

The copolymerization of 9,9-dioctylfluorene (DOF) and thiophene (Th) was successfully achieved by direct anodic oxidation of monomer mixtures on platinum or stainless steel electrodes in boron trifluoride diethyl etherate (BFEE) containing additional 20% diethyl ether (by volume). The incorporation of Th units can produce high quality and freestanding poly(9,9-dioctylfluorene-co-thiophene) [poly(Th-co-DOF)] films with tunable fluorescence properties. As-formed copolymers were characterized by cyclic voltammetry, infrared, UV–visible, fluorescence spectroscopy, and thermal analysis. Copolymers films showed good electrochemical behavior and thermal stability. Fluorescence spectral studies indicated that the copolymer films have strong emissions from 390 to 500 nm, making them good candidates for application as blue–green light-emitting materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Morphological and electroluminescent effects of Au nanoparticles on light-emittingpolymers

A series of light-emitting alternating copolymers, poly(9,9-dioctylfluorene-alt-thiophene) (PDOFT),end-capped with in situ reduced gold nanoparticles have been synthesized (PDOFT-Au). The1H-NMR and 13C-NMR spectra corroborate the well-defined structures, and the XPS spectrum serves as directevidence for the chemical bonding of gold nanoparticles with PDOFTs. All PDOFT-Au(s)are not only soluble in common organic solvents but also have good thermal stability up to380–410 °C. The micrographs of TEM show that the size of gold nanoparticles grows upto 20 nm and the particles aggregate into blocks with an increasing quantity ofHAuCl4. The colour coordinates of PDOFT-Au10 and PDOFT-Au15, (0.237, 0.655) and (0.272,0.649), respectively, are getting close to the standard green (0.26, 0.65) demanded by theNational Television System Committee (NTSC). In conjunction with their goodluminescence properties and photometric efficiencies, PDOFT-Au10 and PDOFT-Au15 aregood candidates for green light-emitting materials. PDOFT with a higher content ofgold nanoparticles, such as PDOFT-Au30, affords a high current density, andthus is a potential candidate for solar cell or organic thin film transistor (OTFT)devices.

A novel green light-emitting material containing both hole and electron transporting units

A novel green light-emitting material containing both hole and electron transporting units

Characteristics of Organic Light-Emitting Diodes Using PECCP Langmuir-Blodgett Film as an Emissive Layer

We have synthesized green light-emitting material, poly(3,6-N−2-ethylhexyl carbazolyl cyanotere-phthalidene)(PECCP), which has an electron-donor and electron-acceptor moiety in a repeated unit of polymer. Organic light-emitting diodes were made with PECCP Langmuir-Blodgett(LB) films in a sandwich structure between indium-tin-oxide(ITO) and aluminum electrodes. Z-type LB films were manufactured using a Kuhn type to use for an emissive layer. We have observed green photoluminescent and electroluminescent spectra at λmax = 536 nm corresponding to 2.31 eV.

Study of Langmuir-Blodgett films of a conjugated poly( 3,6- N- 2-ethylhexyl carbazolyl cyanotere-phthalidene)

Green light-emitting material, poly(3,6-N-2-ethylhexyl carbazolyl cyanotere-phthalidene)(PECCP), was synthesized which has an electron-donor and electron-acceptor moiety in a repeated unit of polymer. We have made PECCP Langmuir-Blodgett(LB) films and they exhibit fluorescence. Organic light-emitting diodes with a single-layer structure (ITO/emitting layer/Al) have been fabricated with the PECCP LB films as an emitting material. We have observed green photoluminescent and electroluminescent spectra at λ max = 536nm corresponding to 2.34eV.