Cesium hydroxide doped tris-(8-hydroxyquinoline) aluminum as an effective electron injection layer in inverted bottom-emission organic light emitting diodes

We demonstrate highly efficient inverted bottom-emission organic light-emitting diodes (IBOLEDs) by using cesium hydroxide (CsOH) doped tris-(8-hydroxyquinoline) aluminum (Alq(3)) as the electron injection layer on indium tin oxide cathode, which could significantly enhance the electron injection, resulting in a large increase in luminance and efficiency. The maximum luminance, current efficiency, and power efficiency reach 21 000 cd/cm(2), 6.5 cd/A, and 3.5 lm/W, respectively, which are 40%-50% higher in efficiency than that of IBOLEDs with cesium carbonate (Cs2CO3) doped Alq(3) as the electron injection layer, where the efficiencies are only 4.5 cd/A and 2.2 lm/W.

White light emission on amplified spontaneous emission with dye content controlled polymer system

White light emission from amplified spontaneous emission (ASE) was realized by optically pumping fluorescent dye 4-(dicy-anomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) doped semiconducting poly(9,9-dioctylfluorene) (PFO) polymer thin films. Two individual ASE peaks originating from DCJTB and PFO were observed by carefully controlling the DCJTB concentration in PFO. The studies of the ASE characteristics of DCJTB:PFO thin films lead to the conclusion that the DCJTB:PFO system with 0.3% w/w DCJTB dopant concentration in PFO showed the best ASE performance.

Enhanced amplified spontaneous emission by assistant Forster energy transfer in DCJTB-C545T-Alq(3) coguest-host system

Amplified spontaneous emission (ASE) characteristics of a red fluorescent dye 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) were significantly improved by assistant Forster energy transfer. The coguest-host system was composed of an electron transport organic molecule tris(8-hydroxyquinoline) aluminum (Alq(3)) as host and a green fluorescent dye (10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano[6,7,8-ij]quinolizin-11-one) (C545T) as assistant dopant codoped with the guest red dye DCJTB as emitter in a matrix of polystyrene (PS).

Realization of blue, green and red emission from top-emitting white organic light-emitting diodes with exterior tunable optical films

We developed an approach to realize blue, green and red emission from top-emitting white organic light-emitting diodes (OLEDs) through depositing exterior tunable optical films on top of the OLEDs. Three primary colors for full color display including blue, green and red emission are achieved by controlling the wavelength-dependent transmittance of the multilayer optical films overlaid on the emissive layer.

Tm3+ and/or Dy3+ doped LaOCl nanocrystalline phosphors for field emission displays

Blue, yellow and white light emissive LaOCl:Tm3+, LaOCl:Dy3+ and LaOCl: Tm3+, Dy3+ nanocrystalline phosphors were synthesized through the Pechini-type sol-gel process. X-Ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), photoluminescence (PL) and cathodoluminescence (CL) spectra were used to characterize the samples. Under UV radiation (229 nm) and low-voltage electron beam (0.5-5 kV) excitation, the Tm3+-doped LaOCl phosphor shows a very strong blue emission corresponding to the characteristic transitions of Tm3+ (D-1(2), (1)G(4) -> F-3(4), H-3(6)) with the strongest emission at 458 nm. The cathodoluminescent color of LaOCl:Tm3+ is blue to the naked eye with CIE coordinates of x = 0.1492, y = 0.0684. This phosphor has better CIE coordinates and higher emission intensity than the commercial product Y2SiO5:Ce3+.

Nanocrystalline LaOCl:Tb3+/Sm3+ as promising phosphors for full-color field-emission displays

Nanocrystalline LaOCl:Tb3+/Sm3+ phosphors were synthesized by a Pechini-type sol-gel process. Under UV and electron-beam excitation, LaOCl:Tb3+/Sm3+ show the characteristic emission of Tb3+ (D-5(3,4) -> F-7(6), ... (2)) and Sm3+ ((4)G(5/2) -> H-6(5/2),(7/2),(9/2)), respectively. In particular, the cathodoluminescence (CL) color of LaOCl:Tb3+ can be tuned from blue to green by changing Tb3+-doped concentration, and their CL intensities (brightness) are higher than those of commercial products Y2SiO5:Ce3+ and ZnO:Zn, respectively. White CL can be realized by codoping with Tb3+ and Sm3+ in a single-phase LaOCl host. The obtained white light is very close to the standard white light. These phosphors are promising for application in field-emission displays.

Simultaneous blue, green, and red emission from diblock copolymer micellar films: a new approach to white-light emission

White-light emission is achieved from a single layer of diblock copolymer micelles containing green- and red-light-emitting dyes in the separate micellar cores and blue-light-emitting polymer around their periphery, in which fluorescence resonance energy transfer between fluorophores is inhibited due to micelle isolation, resulting in simultaneous emission of these three species.

Synthesis and luminescent properties of LaInO3: RE3+ (RE = Sm, Pr and Tb) nanocrystalline phosphors for field emission displays

LaInO3: Sm3+, LaInO3: Pr3+ and LaInO3: Tb3+ phosphors were prepared through a Pechini-type sol-gel process. X-ray diffraction, field emission scanning electron microscopy, photoluminescence, and cathodoluminescence (CL) spectra were utilized to characterize the synthesized phosphors. XRD results reveal that the pure LaInO3 phase can also be obtained at 700 degrees C. FE-SEM images indicate that the LaInO3: Sm3+, LaInO3: Pr3+ and LaInO3: Tb3+ phosphors are composed of aggregated spherical particles with sizes around 80-120 nm. Under the excitation of ultraviolet light and low voltage electron beams (1-5 kV), the LaInO3: Sm3+, LaInO3: Pr3+ and LaInO3: Tb3+ phosphors show the characteristic emissions of Sm3+ ((4)G(5/2)-H-6(5/2,7/2,9/2) transitions, yellow), Pr3+ (P-3(0)-H-3(4), P-3(1)-H-3(5), D-1(2)-H-3(4) and P-3(0)-F-3(2) transitions, blue-green) and Tb3+ (D-5(4)-F-7(6.5,4.3) transitions, green) respectively. The corresponding luminescence mechanisms are discussed. These phosphors have potential applications in field emission displays.

Harvesting Excitons Via Two Parallel Channels for Efficient White Organic LEDs with Nearly 100% Internal Quantum Efficiency: Fabrication and Emission-Mechanism Analysis

By incorporating two phosphorescent dyes, namely, iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C-2']picolinate (Flrpic) for blue emission and bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1 H-benzoimidazol-N,C-3) iridium(acetylacetonate) ((fbi)(2)Ir(acac)) for orange emission, into a single-energy well-like emissive layer, an extremely high-efficiency white organic light-emitting diode (WOLED) with excellent color stability is demonstrated. This device can achieve a peak forward-viewing power efficiency of 42.5 lm W-1, corresponding to an external quantum efficiency (EQE) of 19.3% and a current efficiency of 52.8 cd A(-1). Systematic studies of the dopants, host and dopant-doped host films in terms of photophysical properties (including absorption, photoluminescence, and excitation spectra), transient photoluminescence, current density-voltage characteristics, and temperature-dependent electroluminescence spectra are subsequently performed, from which it is concluded that the emission natures of Flrpic and (fbi)(2)Ir(acac) are, respectively, host-guest energy transfer and a direct exciton formation process. These two parallel pathways serve to channel the overall excitons to both dopants, greatly reducing unfavorable energy losses.

High efficiency fluorescent white organic light-emitting diodes with red, green and blue separately monochromatic emission layers

Highly efficient fluorescent white organic light-emitting diodes (WOLEDs) have been fabricated by using three red, green and blue, separately monochromatic emission layers. The red and blue emissive layers are based on 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) doped N,N'-di(naphthalene-1-yl)-N,N'-diphenyl-benzidine (NPB) and p-bis(p-N,N-diphenyl-amino-styryl) benzene (DSA-ph) doped 2-methyl-9,10-di(2-naphthyl) anthracene (MADN), respectively; and the green emissive layer is based on tris(8-hydroxyquionline)aluminum(Alq(3)) doped with 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl- 1H,5H,1[H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-1]-one (C545T), which is sandwiched between the red and the blue emissive layers. It can be seen that the devices show stable white emission with Commission International de L'Eclairage coordinates of (0.41, 0.41) and color rendering index (CRI) of 84 in a wide range of bias voltages.

Origin of improvement in device performance via the modification role of cesium hydroxide doped tris(8-hydroxyquinoline) aluminum interfacial layer on ITO cathode in inverted bottom-emission organic light-emitting diodes

It has been found that cesium hydroxide (CsOH) doped tris(8-hydroxyquinoline) aluminum (Alq(3)) as an interfacial modification layer on indium-tin-oxide (ITO) is an effective cathode structure in inverted bottom-emission organic light-emitting diodes (IBOLEDs). The efficiency and high temperature stability of IBOLEDs with CsOH:Alq(3) interfacial layer are greatly improved with respect to the IBOLEDs with the case of Cs2CO3:Alq(3). Herein, we have studied the origin of the improvement in efficiency and high temperature stability via the modification role of CsOH:Alq(3) interfacial layer on ITO cathode in IBOLEDs by various characterization methods, including atomic force microscopy (AFM), ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS) and capacitance versus voltage (C-V). The results clearly demonstrate that the CsOH:Alq(3) interfacial modification layer on ITO cathode not only enhances the stability of the cathode interface and electron-transporting layer above it. which are in favor of the improvement in device stability, but also reduces the electron injection barrier and increases the carrier density for current conduction, leading to higher efficiency.

ZnO Nanorods as Scatterers for Random Lasing Emission from Dye Doped Polymer Films

A random lasing emission from 4-(dicy-anomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) doped polystyrene (PS) thin films was realized by the scattering role of ZnO nanorods. The device was fabricated by spin-coating DCJTB doped PS on ZnO nanorods. The ZnO nanorods were grown on indium-tin-oxide (ITO) glass substrate by hydrothermal synthesis method. It can be seen that the device emits a resonance multimode peak at center wavelength of 630 nm with a mode line-width of less than 0.23 nm and exhibits threshold excitation intensity as low as 0.375 mJ pulse(-1) cm(-2). The agreement of the dependence of threshold pumped intensity on the excitation area with the random laser theory indicates that the lasing emission realized here is random laser. Our results demonstrate that the nanostructured ZnO nanorods are promising candidate as alternative sources of coherent light emission to realize organic lasers.

Simple and Efficient Near-Infrared Organic Chromophores for Light-Emitting Diodes with Single Electroluminescent Emission above 1000 nm

A series of NIR organic chromophores with donor-pi-acceptor-pi-donor structure are synthesized. Good thermal stability and strong photoluminescence in solid state render them suitable for application in light-emitting diodes. Exclusive near-infrared emission at 1080 nm with external quantum efficiency of 0.28% is obtained from the nondoped OLEDs. The longest electroluminescence wave-length is 1220 nm.

Enhanced amplified spontaneous emission using layer-by-layer assembled cowpea mosaic virus

Layer-by-layer assembly technique was used to construct ultrathin film of cowpea mosaic virus (CPMV) by electrostatic interactions, and the film was employed as a precursor on which an OF8T2 film was deposited by spin coating. Amplified spontaneous emission (ASE) was observed and improved for the OF8T2 film. Compared with OF8T2 film on quartz, the introduction of CPMV nanoparticles reduced the threshold and loss, and remarkably increased the net gain. The threshold, loss, and gain reached 0.05 mJ/ pulse, 6.9 cm(-1), and 82 cm(-1), respectively. CPMV nanoparticles may enormously scatter light, resulting in a positive feedback, thus the ASE is easily obtained and improved.

Thermoluminescence characteristics of NaSr4(BO3)(3):Ce3+ under beta-ray irradiation

The thermoluminescence (TL) properties of Ce3+ doped NaSr4(BO3)(3) phosphor under the beta-ray irradiation were reported. The polycrystalline sample was synthesized by high temperature solid-state reaction. The TL glow curve of NaSr4(BO3)(3):Ce3+ phosphor was composed of only one peak. TL kinetic parameters of NaSr4(BO3)(3):Ce3+ were deduced by the peak shape method, the activation energy (E) was 0.590 eV and the frequency factor was 1.008x10(6) s(-1). TL dose response was linear in the range of measurement. The 3-dimensional (3D) TL emission spectrum was also recorded, the emission spectrum consisted of two bands located at 441 and 479 nm respectively, corresponding to the characteristic 4f(0)5d(1)-> F-2((5/2,7/2)) transitions of the Ce3+ ion. The fading behavior of the NaSr4(BO3)(3):Ce3+ phosphor over a period of 15 d was also studied.