Qihuang Gong

Recent Progresses on Materials for Electrophosphorescent Organic Light‐Emitting Devices

Although organic light-emitting devices have been commercialized as flat panel displays since 1997, only singlet excitons were emitted. Full use of singlet and triplet excitons, electrophosphorescence, has attracted increasing attentions after the premier work made by Forrest, Thompson, and co-workers. In fact, red electrophosphorescent dye has already been used in sub-display of commercial mobile phones since 2003. Highly efficient green phosphorescent dye is now undergoing of commercialization. Very recently, blue phosphorescence approaching the theoretical efficiency has also been achieved, which may overcome the final obstacle against the commercialization of full color display and white light sources from phosphorescent materials. Combining light out-coupling structures with highly efficient phosphors (shown in the table-of-contents image), white emission with an efficiency matching that of fluorescent tubes (90 lm/W) has now been realized. It is possible to tune the color to the true white region by changing to a deep blue emitter and corresponding wide gap host and transporting material for the blue phosphor. In this article, recent progresses in red, green, blue, and white electrophosphorescent materials for OLEDs are reviewed, with special emphasis on blue electrophosphorescent materials.

A Facile One‐step Method to Produce Graphene–CdS Quantum Dot Nanocomposites as Promising Optoelectronic Materials

[*] Prof. A. Cao, Z. Liu, Prof. M. Wu, Z. Ye, Z. Cai, Y. Chang, Prof. Y. Liu Institute of Nanochemistry and Nanobiology Shanghai University, Shanghai, 200444 (P. R. China) E-mail: ancao@shu.edu.cn Prof. S. Wang, S. Chu, Prof. Q. Gong State Key Laboratory for Mesoscopic Physics, School of Physics Peking University, Beijing, 100871 (P. R. China) E-mail: wangsf@pku.edu.cn Prof. Y. Liu Beijing National Laboratory of Molecular Science College of Chemistry and Molecular Engineering Peking University, Beijing, 100871 (P. R. China) E-mail: yliu@pku.edu.cn

Engineering of Electron-Selective Contact for Perovskite Solar Cells with Efficiency Exceeding 15%

The past 5 years have witnessed the rise of highly efficient organometal halide perovskite-based solar cells. In conventional perovskite solar cells, compact n-type metal oxide film is always required as a blocking layer on the transparent conducting oxide (TCO) substrate for efficient electron-selective contact. In this work, an interface engineering approach is demonstrated to avoid the deposition of compact n-type metal oxide blocking film. Alkali salt solution was used to modify the TCO surface to achieve the optimized interface energy level alignment, resulting in efficient electron-selective contact. A remarkable power conversion efficiency of 15.1% was achieved under AM 1.5 G 100 mW · cm(-2) irradiation without the use of compact n-type metal oxide blocking layers.

Reduction in feature size of two-photon polymerization using SCR500

Fabricated by femtosecond laser pulses at wavelength λ of 780nm, the feature size of two-photon polymerization using SCR500 was reduced to λ∕50. Lines with sub-25-nm width were produced by controlling the incident laser power and the laser focus scan speed up to 700μm∕s. Based on repolymerization between two structures close to each other, the feature size was further reduced to ∼15nm, which demonstrated the potential for three-dimensional nanofabrication with high spatial resolution.

Detection of Single Nanoparticles and Lentiviruses Using Microcavity Resonance Broadening

A new label-free sensing mechanism is demonstrated experimentally by monitoring the whispering-gallery mode broadening in microcavities. It is immune to both noise from the probe laser and environmental disturbances, and is able to remove the strict requirement for ultra-high-Q mode cavities for sensitive nanoparticle detection. This ability to sense nanoscale objects and biological analytes is particularly crucial for wide applications.

Plasmon-induced transparency in asymmetric T-shape single slit.

By utilizing a dielectric-film-coated asymmetric T-shape single slit, comprising two grooves of slightly detuned widths immediately contacting with a single nanoslit, the plasmon-induced transparency was experimentally demonstrated. Because of the symmetry breaking in the unit-cell structure, the scattered lights from the two grooves with slightly detuned widths interfere destructively, leading to the plasmon-induced transparency. As a result, a response spectrum with nearly the same interference contrast but a much narrower bandwidth emerges in the unit-cell structure with the footprint of only about 0.9 μm(2), compared with that in the symmetric T-shape single slit. These pronounced features in the structure, such as the increased quality factor, ultracompact size, easy fabrication, and experimental observation, have significant applications in ultracompact plasmonic devices.

Single nanoparticle detection using split-mode microcavity Raman lasers

Significance Optical sensing with ultrahigh sensitivity of single nanoscale objects is strongly desirable for applications in various fields, such as in early-stage diagnosis of human diseases and in environmental monitoring, as well as in homeland security. In this article, we report an optical technique for single nanoparticle detection in both air and an aqueous environment, with an ultralow detection limit. Ultrasensitive nanoparticle detection holds great potential for early-stage diagnosis of human diseases and for environmental monitoring. In this work, we report for the first time, to our knowledge, single nanoparticle detection by monitoring the beat frequency of split-mode Raman lasers in high-Q optical microcavities. We first demonstrate this method by controllably transferring single 50-nm–radius nanoparticles to and from the cavity surface using a fiber taper. We then realize real-time detection of single nanoparticles in an aqueous environment, with a record low detection limit of 20 nm in radius, without using additional techniques for laser noise suppression. Because Raman scattering occurs in most materials under practically any pump wavelength, this Raman laser-based sensing method not only removes the need for doping the microcavity with a gain medium but also loosens the requirement of specific wavelength bands for the pump lasers, thus representing a significant step toward practical microlaser sensors.

Efficient unidirectional generation of surface plasmon polaritons with asymmetric single-nanoslit

An asymmetric single-nanoslit composed of a conventional nanoslit with a nanogroove next to it in a metallic film is proposed to generate unidirectional surface plasmon polaritons (SPPs) efficiently with back-side illumination. Numerical simulations show that due to the different interference processes of SPPs to opposite directions, efficient unidirectional SPP generation can be achieved. Experimentally, an extinction ratio of about 30:1 for SPPs to opposite directions and a generation efficiency of about 1.8 times that of the symmetrical case are demonstrated at wavelength of 830 nm with the lateral dimension of the asymmetric single-nanoslit of only 370 nm.

Measurement of spin Hall effect of reflected light

We have measured the spin-dependent nanometer-sized displacements of the spin Hall effect of the reflected light from a planar air-glass interface. In the case of the vertical polarization, the displacement is found to increase with the incident angle and subsequently decrease after approximately 48 deg, while in the case of the horizontal polarization, it changes rapidly near the Brewster angle. For a fixed incident angle of 30 deg, the displacement decreases to zero as the polarization angle approaches approximately 39 deg from 0 deg (the horizontal polarization) and then increases in the opposite direction until 90 deg (the vertical polarization).

Direct measurement of propagation losses in silver nanowires.

Propagation losses of surface plasmons in single silver nanowire waveguides were obtained by measuring light intensity at the end of a silver nanowire. Surface plasmons were excited directly by a tapered fiber. A typical propagation loss of 0.53 dB/εm was obtained.