Pure Blue Light Emission Research Articles

Sterically Controlled Synthesis of Amine-Free CsPbBr3 Nanoplatelets for Stable, Pure-Blue Light Emission.

Metal halide perovskite nanoplatelets (NPLs) have demonstrated excellent optical properties for light-emitting applications and achieved tunable blue luminescence through thickness control. However, their translation into electronic devices has lagged behind due to poor colloidal and film stability. The main reason for this is the deprotonation of their surface-capped ammonium passivating ligands, resulting in NPL aggregation. Here we report the first facile synthesis of amine-free pure-blue CsPbBr3 NPLs with outstanding thermal and light stability. This is achieved by utilizing an amine-free phosphine oxide route with a surface capping molecule exhibiting large steric hindrance to prevent NPL aggregation. Two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy suggests slower ligand exchange in amine-free NPLs compared to the conventional NPLs, which can be attributed to the strong binding strength of the designated ligand. Consequently, the amine-free NPLs exhibited superior stability against radiation, heat and moisture. We further demonstrate the importance of acid-base equilibrium in this amine-free synthesis route. Through solvent neutralization and passivation with various alkali carbonates, the resulting NPLs attained near-unity photoluminescence quantum yield (PLQY) and pure blue emission.

Synthesis, Photophysical Studies of Blue‐Light‐Emitting Alternating Polymers from Substituted 9‐Sila Fluorenes and Substituted p‐Phenylacene

AbstractFive new alternating polymers were synthesized from 2,7‐dibromo‐3,6‐dimethoxy‐9‐sila fluorene with varied alkyl and aryl groups substituted at 9‐position and 2‐tert butyl‐9,10‐di (p hydroxyl phenyl) anthracene. The monomers and the polymers were synthesized in good yields at each stage of preparation and with high degree of reproducibility. The copolymers were soluble in common organic solvents like toluene, xylene, THF and chloroform. Chemical and optoelectronic characterizations of the polymers were done by 1H and 13C NMR, GPC, UV absorption, photoluminescence and cyclic voltammetric studies. Pure blue light emission, with the maximum absorption wavelength in the range of 445 to 457 nm and the PL quantum efficiency in the range of 0.55 to 0.91 were recorded for the synthesized copolymers in their solution in CHCl3. The ITO/CuPc/α‐NPD/ copolymer/ Alq3/LiF/Al devices fabricated from the polymers gave pure blue light emission irrespective of the substitution on silicon atom of the silafluorene moiety. The properties both photophysical and electrochemical, of the synthesized alternating polymers are quite suitable for the development of blue light emitting devices.

Synthesis and properties of blue-light-emitting Oligo(fluorene-co-dibenzothiophene-S,S-dioxide)s

An effective synthetic route for preparation of oligo(fluorene-co- dibenzothiophene-S,S-dioxide)s (trimer SOF2, pentamer SOF4, heptamer SOF6 and nonamer SOF8) based on meta- or para-linked dibenzothiophene-S,S-dioxide (SO) unit as the core was developed by convergence method, for which the intermediates unilateral boric acid esters were prepared by one-step palladium-catalysed Suzuki cross-coupling reaction. The resulting oligomers exhibited excellent thermal stability with thermal decomposition temperature exceeding 415 °C, and high photoluminescent quantum yield in the solid state (52–81%). The UV–vis absorption and photoluminescence emission maxima of the oligomers exhibited gradual bathochromic shifts from the trimer to the nonamer, approaching those of the previously reported polymer PFSO10 containing 10 mmol% of the SO unit in the polyfluorene backbone, demonstrating the similar photophysical properties of the nonamer SOF8 and polymer PFSO10. The highest occupied molecular orbital energy level gradually decreased and the lowest unoccupied molecular orbital energy level steadily increased from the trimer SOF2 to the nonamer SOF8. The obtained oligomers displayed pure blue-light emission with the maximal emission peaked at about 440 nm and superior EL spectral stability compared with PFSO10 upon varying the current density from 100 mA cm−2 to 500 mA cm−2, in addition to more balanced hole and electron fluxes. With the device configuration of ITO/PEDOT:PSS/oligomer/CsF/Al, a maximum luminous efficiency of 2.75 cd A−1 with Commission Internationale de l’Eclairage (CIE) coordinates of (0.16, 0.15) was obtained for the device based on 37SOF8. The efficiency increased by 88% compared with the device based on 37PFSO10 (1.46 cd A−1). A similar enhancement in efficiency was also achieved for the device based on 28SOF8. These results indicate that the obtained oligomers are very promising candidates for structurally well-defined blue-light- emitting materials with high efficiency and reproducibility.

Rapid and facile synthesis of graphene oxide quantum dots with good linear and nonlinear optical properties

We herein report a rapid and effective method for the synthesis of graphene oxide quantum dots (GOQDs) with excellent linear and nonlinear optical properties. The GOQDs were prepared by chemical cutting of graphite oxide and characterized using Fourier transform infrared spectroscopy, X-ray diffraction, UV–Vis absorption spectroscopy, Raman spectroscopy and transmission electron microscopy. The Commission International de l’Eclairage 1931 chromaticity coordinates for GOQDs (x = 0.21, y = 0.23) demonstrated that highly pure blue-light emission was achieved upon 330 nm excitation wavelength. Optical nonlinearity measurements conducted at 532 nm using 5 ns laser pulses indicated saturable absorption behavior, which tends to the onset of reverse saturable absorption as the input light fluence was increased.

Pure blue light-emitting fluorene-based conjugated polymer with excellent thermal, photophysical, and electroluminescent properties

A functionalized polyfluorene (FPF) with dendritic carbazole and oxadiazole side chains have been successfully designed, synthesized, and characterized. The weight-average molecular weight (M w) and number-average molecular weight (M n) were measured by gel permeation chromatography (GPC) to be 71280 and 31185, respectively. The FPF is thermally stable with high decomposition temperature (T d = 495 °C) and glass transition temperature (T g = 160 °C), and show good solubility in organic solvents, such as N,N-dimethyl formamide, tetrahydrofuran, CHCl3, and toluene. The photoluminescent and electroluminescent (EL) emissions and Commission Internationale de L’Eclairage coordinates indicated pure blue light emission of FPF and its device. The luminance–voltage (L–V) and current density–voltage (J–V) characteristics of the devices based on FPF indicated typical diode characteristics with a maximum luminance of 980 cd/m2 at a drive voltage of 13.0 V, a maximum current density of 726 mA/cm2, and a turn-on voltage of 8.54 V. The maximum EL efficiency of the device based on FPF was measured to be 0.46 % at the current density of 12.5 mA/cm2. These results indicate that the FPF polymer could be a promising candidate for pure blue light-emitting polymer with excellent thermal, photophysical, and electroluminescent properties.

Pure blue electroluminescent poly(aryl ether)s with dopant-host systems

A series of novel arylene ether polymers (P5F-BCzVFs) containing both pentafluorene (5F) and distyrylarylene derivative (BCzVF) units in the side chains for efficient pure blue light emission were prepared by a facile, metal-free condensation polymerization. The emission spectra indicated that color tuning could be achieved through efficient Förster energy transfer from the deep-blue 5F host to the pure-blue BCzVF dopant. Single-layer polymer light-emitting diodes (PLEDs) based on P5F-BCzVFs (ITO/(PEDOT:PSS)/polymer/Ca/Al) exhibited voltage-independent and stable pure blue emission with a Commission International de L'Eclairage (CIE) coordinate of (0.15, 0.15), a maximum brightness of 3576 cd/m2, and a maximum luminous efficiencies of 2.15 cd/A, respectively. As most polymers with dopant-host systems, the luminous efficiencies of all P5F-BCzVFs surpassed that of the host-only polymer (P5F), due to the energy transfer and charge trapping from the host to the dopant. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Pure Blue-Light-Emitting Materials: Hyperbranched Ladder-Type Poly(p-phenylene)s Containing Truxene Units

A series of novel hyperbranched ladder-type poly(p-phenylene)s containing truxene units have been prepared through the Pd(0)-catalyzed Suzuki polymerization with an “A2 + B3” or “A2 + B2+ B3” approach. The polymers with different linear length show pure blue light emission from 417 to 465 nm. All the ladder-type polymers exhibit well-resolved absorption and emission spectra and small Stokes shifts in both solutions and thin films, which are the characteristics of full ladder-type poly(p-phenylene)s. The three-dimensional structures make the materials soluble in common organic solvents and able to form quality amorphous films, leading to polymer light-emitting diodes (PLEDs) with improved stability and efficiency.

Modelling of strained ZnSSe on relaxed ZnSSe-based structures for blue light emission

It has been a long time since the start of successful production in laboratory of light-emitting devices based on wide bandgap II–VI semiconductors, but the applications have been limited by the luck of materials that can emit blue light efficiently. In this work, we propose and model a ZnS x Se 1− x -based structure emitting blue light and resolve many defect problems due to the lack of substrates of ZnSSe-epitaxy. The optoelectronic properties of (n-ZnS 0.8Se 0.2-relaxed/(ZnSe/ZnS 0.2Se 0.8/ZnSe)-strained/n-ZnS 0.8Se 0.2-relaxed) and (n-ZnS 0.8Se 0.2-relaxed/triple quantum well (QW) (ZnSe/ZnS 0.2Se 0.8/ZnSe)-strained/ n-ZnS 0.8Se 0.2-relaxed) are studied and compared. The numerical self-consistent resolution of Schrödinger–Poisson equations leads to the potential profiles of conduction and valence bands. Variation of ZnSe /ZnS 0.2Se 0.8/ZnSe well thickness permits to optimize the confinement of electrons and heavy holes, the wave function overlap, the oscillator strength and the carrier density for the two structures. The optimized results show that pure blue light emission is achieved more efficiently with the second proposed stack using a triple ZnSe/ZnS 0.2Se 0.8/ZnSe QW in the active layer.

Fluorescent Blue Materials for Efficient Organic Light-Emitting Diode with High Color Purity

We report a new series of blue dopants composed of both electron donating and electron accepting moieties in one molecule, based on nalidixic acid. The EL device derived from the dopant exhibits pure blue light emission (0.15, 0.14) The current efficiency is estimated to be 3.88 cd/A at 100 , which shows remarkable enhancement, compared to that of the host itself (2.5 cd/A at 100 ) under the same conditions. These results demonstrate that the incorporation of a proper guest into the host in a guest-host doped system improves not only the purity of the fluorescent blue emission but also elevates its quantum efficiency, thus improving the OLED performance.

Blue-emitting cyanuric acid–melamine complexes from urea thermolysis

Novel blue-emitting cyanuric acid–melamine complexes CA x ·M 1− x ( x = 0.8–0.9) have been prepared by a simple two-step procedure from urea. Relatively strong and pure blue-light emission with a maximum at 470 nm was observed from these complexes. These complexes are very promising light-emitting materials due to their good thermal stability.

Synthesis and fluorescence of polymeric triphenylamine obtained by oxidative‐coupling polymerization

AbstractWe prepared triphenylamine (TPA)‐containing polymers by a direct oxidative‐coupling method, which showed high thermostability, good solubility, high quantum efficiency, and blue light emission. The polymers are characterized by Fourier transform infrared spectroscopy, 1H‐NMR, ultraviolet–visible spectroscopy, thermogravimetric analysis, elemental analysis, and fluorescence spectra. The homopolymeric TPA (PTPA) was fairly soluble in CCl4 and toluene, with a quantum yield of 0.38 relative to Rhodamine B in toluene solution, and showed blue light emission in solid‐state film. The TPA–stilbene copolymers were more soluble than the PTPA and showed violet to green light emission in solid‐state film, depending on the TPA moiety contents, from which a pure blue light emission could be obtained. The emitting quantum efficiency of the copolymers measured in toluene solution was from 0.57 to 0.78 relative to Rhodamine B. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2718–2724, 2002

Blue Electroluminescence from ZnSe p-n Junction Light-Emitting Diodes

Pure blue-light emission has been obtained from homoepitaxial ZnSe p-n junction light-emitting diodes (LEDs). Homoepitaxy is made on ZnSe substrates dry-etched by a BCl3 plasma. High-quality p-n junctions consists; of N-doped p-type ZnSe formed by active-nitrogen doping and Cl-doped n-type ZnSe using ZnCl2 as a dopant source. Current-voltage characteristics of the LEDs exhibited good rectification properties. The peak energy of blue electroluminescence from the LEDs was 2.67 eV with a narrow full width at half-maximum of 49 meV.

Blue light emission from ZnSe p-n junctions

Pure blue light emission has been obtained from ZnSe p-n junctions. ZnSe crystals are grown by the temperature difference solution growth method under controlled vapor pressure. A p-type ZnSe crystal can be grown from Se solution by doping with a group I element under controlled Zn pressure. The properties of p-type crystals have been measured by the van der Pauw method. A p-n junction has been made by the formation of the n-type layer by Ga diffusion into the p-type crystal. The fundamental properties of the p-n junctions are as follows: the value of n in the I-V characteristics ranges from 1.4 to 1.8 and the diffusion potential is between 2.5 and 2.7 eV. The emission spectrum from the p-n junction depends on the vapor pressure during growth and blue light emission is obtained with optimum pressure. The wavelength of the main emission peak is 460 nm at 77 °K and 480 nm at 300 °K. The brightness is 2 mcd at 2 mA.