Charge-transporting organic semiconductors are an important class of materials that play crucial roles in electronic and optoelectronic devices such as organic light-emitting devices (OLEDs), [1] thin film transistors, and photovoltaic cells.OLEDs, that have organic hole-and electron-transport layers sandwiched between two electrodes, show low driving voltage and bright emission and are of importance for application to full color flat-panel displays and lighting. Since electron mobilities in organic materials, in general, are several orders of magnitude lower than hole mobilities, [2] electron-transport materials (ETMs) with high electron mobility are required to further improve OLED performance. To achieve an effective electron injection and transport in an OLED, a high conductive n-doped electron-transport layer is developed by Kido [3] and Leo [4,5] by coevaporation of ETM and highly active alkaline metal of Li and Cs. In this case, a hole-and exciton-block buffer layer is indispensable to prevent exciton quenching in the emissive layer by the dopants in the electron-transport layer. This may induce more complexity of device structure and thus higher cost for applications to flat-panel displays and lighting. Forrest and Thompson's group has proposed a way to break through the efficiency limitation by using phosphorescent emitting materials. This renders possible harvesting both electro-generated singlet and triplet excitons for emission from OLEDs and realizing nearly 100% internal quantum efficiencies of electroluminescence. [6,7] It is essential that the triplet excited states of all the corresponding materials should be higher than that of the phosphorescent emitter to confine the generated triplet excitons in the emissive layer. To match this request, the conjugation length of the material must be limited to achieve high triplet energy levels. However, it is difficult to meet these requirements because there is a tradeoff between increasing the band gap of the material to increase singlet and triplet energies and decreasing the p-conjugation system, which may adversely affect the charge transport properties.[8]As such, it becomes particularly challenging to develop carrier transport materials with high triplet energy levels especially for a blue triplet emitter. In this communication, we report two pyridine-containing triphenylbenzene derivatives of 1,3,5-tri(m-pyrid-3-yl-phenyl) benzene (TmPyPB) and 1,3,5-tri( p-pyrid-3-yl-phenyl)benzene (TpPyPB), which possess both high electron mobilities and high triplet energy levels. High external quantum efficiency and power efficiency are realized for the iridium (III) bis(4,6-(di-fluorophenyl)pyridinato-N,C 2 0 ) picolinate (FIrpic)-based blue phosphorescent OLED and the fac-tris(2-phenylpyridine) iridium (Ir(PPy) 3 )-based green phosphorescent OLED using TmPyPB and TpPyPB as the ETMs, respectively.Scheme 1 depicts the synthetic routes of TmPyPB and TpPyPB. They were synthesized by the Suzuki cross-coupling reaction between 3-(4,4,5,5-tetramethyl-1,3,2-dioxaboro...

Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general illumination, backlighting, and laser-driven lighting. Finally, the challenges and outlooks in this type of promising down-conversion materials are highlighted.

A record high efficiency and reduced efficiency roll-off were achieved for blue phosphorescent OLEDs with novel bipolar host materials containing both carbazole electron donor and pyridine electron acceptor because of good confinement of triplet excitons on the guest molecules and improved carrier balance injected into the emissive layer.

The crystal structure and photoluminescence properties of undoped and Ce3+-doped CaAlSiN3 as well as the application of white-light LEDs are reported. CaAlSiN3 and CaAlSiN3:Ce3+ have been synthesized, starting from Ca3N2, AlN, Si3N4, and CeN or CeO2 with and without Li3N, by a solid state reaction at 1700 °C for 4 h under high purity nitrogen atmosphere. Instead of an ideal CaAlSiN3, a more appropriate formula is proposed to be CaAl1−4δ/3Si1+δN3 (δ ≈ 0.3−0.4) with an Al/Si ratio of about 1:2 on the basis of the bond valence sum calculations, in which Al/Si is disorderly occupied on the 8b site within Cmc21 space group. Ce3+ can be incorporated into the host lattice of CaAlSiN3, and the estimated maximum solubility of Ce3+ is about x = 0.02 (e.g., 2.0 mol % with respect to Ca) of Ca1−2x Ce x Li x AlSiN3. CaAlSiN3:Ce3+ can be efficiently excited by blue light (450−480 nm) and yields yellow-orange emission with a broadband peaking in the range of 570−603 nm, originating from the 5d1 → 4f1 transition of Ce3+. With an increase of Ce concentration, the emission band of Ce3+ shifts to longer wavelengths due to the increased Stokes shift corresponding to structural relaxation and energy transfer of Ce3+. Upon excitation in blue light range (450−480 nm), the absorption and external quantum efficiency are about 70% and 56%, respectively, for both Ca1−2x CexLixAlSiN3 and Ca1−x CexAlSiN3−2x/3O3x/2 at x = 0.01. In addition, Ca1−2x Ce x Li x AlSiN3 and Ca1−x Ce x AlSiN3−2x/3O3x/2 show high thermal stability in air with the quenching temperature above 300 °C for x = 0.01. Using single CaAlSiN3:Ce3+ as the wavelength conversion phosphor combined with a blue InGaN LED-chip (450 nm), warm white-light LEDs can be generated, yielding the luminous efficacy of about 50 lm/W at color temperature 3722 K and the color rendering index (Ra) of 70, which demonstrates that CaAlSiN3:Ce3+ is a highly promising yellow-orange phosphor for use in white-light LEDs.

Nitridosilicates are structurally built up on three-dimensional SiN4 tetrahedral networks, forming a very interesting class of materials with high thermomechanical properties, hardness, and wide band gap. Traditionally, nitridosilicates are often used as structural materials such as abrasive particles, cutting tools, turbine blade, etc. Recently, the luminescence of rare earth doped nitridosilicates has been extensively studied, and a novel family of luminescent materials has been developed. This paper reviews the synthesis, luminescence and applications of nitridosilicate phosphors, with emphasis on rare earth nitrides in the system of M-Si-Al-O-N (M = Li, Ca, Sr, Ba, La) and their applications in white LEDs. These phosphors exhibit interesting luminescent properties, such as red-shifted excitation and emission, small Stokes shift, small thermal quenching, and high conversion efficiency, enabling them to use as down-conversion luminescent materials in white LEDs with tunable color temperature and high color rendering index.