Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

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Lanthanide luminescence for functional materials and bio-sciences

Slow light with a remarkably low group velocity is a promising solution for buffering and time-domain processing of optical signals. It also offers the possibility for spatial compression of optical energy and the enhancement of linear and nonlinear optical effects. Photonic-crystal devices are especially attractive for generating slow light, as they are compatible with on-chip integration and room-temperature operation, and can offer wide-bandwidth and dispersion-free propagation. Here the background theory, recent experimental demonstrations and progress towards tunable slow-light structures based on photonic-band engineering are reviewed. Practical issues related to real devices and their applications are also discussed. The unique properties of wide-bandwidth and dispersion-free propagation in photonic-crystal devices have made them a good candidate for slow-light generation. This article gives the background theory of slow light, as well as an overview of recent experimental demonstrations based on photonic-band engineering.

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Slow light in photonic crystals

Organic semiconductor lasers.

Organic light emitting devices are disclosed which are comprised of a heterostructure for producing electroluminescence wherein the heterostructure is comprised of an emissive layer containing a phosphorescent dopant compound. For example, the phosphorescent dopant compound may be comprised of platinum octaethylporphine (PtOEP), which is a compound having the chemical structure with the formula:

OLEDs doped with phosphorescent compounds

This Focus Review describes the emerging class of near-infrared (NIR) organic compounds containing the conjugated polyene, polymethine, and donor-acceptor chromophores and exploration of their NIR-absorbing, NIR-fluorescence, and NIR-photosensitizing properties for potential applications in heat absorbers, solar cells, and NIR light-emitting diodes Examples of NIR organic compounds are reviewed with emphasis on the molecular design, NIR absorption, and fluorescence and particular emerging applications The donor-acceptor type of NIR chromophores are particularly introduced owing to some unique features, including the designer-made energy gaps, facile synthesis, good processability, and controllable morphology and properties in the solid state Future directions in research and development of NIR organic materials and applications are then offered from a personal perspective

Near‐Infrared Organic Compounds and Emerging Applications

We fabricated a series of two-dimensional (2D) hexagonal organic photonic-crystal lasers whose lattice constant varies from 0.18 to 0.44 μm, and observed clear lasing oscillation at the four lowest band gap frequencies (M1, K2, M2, and Γ1). We used in-plane beam propagation analysis to clarify the 2D feedback mechanism at each gap frequency, which differs for different gaps. The observed K1 lasing oscillation is due to coupling of three nonparallel diffracted waves, which has a purely 2D character. This shows that photonic crystal lasers can operate with various feedback essentially different from that of conventional 1D distributed feedback lasers.

Directional lasing oscillation of two-dimensional organic photonic crystal lasers at several photonic band gaps

We have fabricated photonic quasicrystal lasers with a Penrose lattice that does not possess translational symmetry but has long-range order, and observed coherent lasing action due to the optical feedback from quasiperiodicity, exhibiting a variety of 10-fold-symmetric lasing spot patterns. The lattice constant dependence of lasing frequencies and spot patterns show complicated features very different from photonic crystal/random lasers, and we have quantitatively explained them by considering their reciprocal lattice. Unique diversity of their reciprocal lattice opens up new possibilities for the form of lasers.

Lasing action due to the two-dimensional quasiperiodicity of photonic quasicrystals with a Penrose lattice

We have devised a novel device structure for a multiple quasi-phase-matched wavelength converter. Optimized continuous phase modulation of a periodic domain structure makes possible multichannel pumping with minimum loss of efficiency. Using the device, we demonstrate variable and simultaneous wavelength conversion of wavelength-division multiplexed signals.

Multiple quasi-phase-matched LiNbO3 wavelength converter with a continuously phase-modulated domain structure.

This paper outlines our recent efforts to develop organic infrared (IR) and near-infrared (NIR) light-emitting materials and devices for use in optical communication technology. The IR and NIR light-emitting materials investigated are two organic ionic dyes, (2-[6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl]-3-methyl-benzothiazonium perchlorate) (LDS821) and [C41H33Cl2N2]+·BF4− (IR1051), and an organic rare-earth complex, erbium (III) tris(8-hydroxyquinoline) (ErQ). These materials exhibit photo- and electro-luminescence in the 0.8-, 1.1- and 1.5-μm wavelength regions, respectively. They were used as optically active species in the following three device forms; vacuum-deposited or doped spin-coated polymer thin-films, doped monodispersed polymer microparticles, and embedded polymeric optical waveguides with a doped core. I propose possible optical communication applications based on their optical properties and luminescent processes.

Organic light-emitting materials and devices for optical communication technology

By combining a high-efficiency nonlinear optical crystal with a high-output semiconductor laser for optical communication, a small-sized laser light source the wavelength of which can be freely designed in a wavelength range not practically used by semiconductor lasers is provided. An example comprises a first laser that emits a laser beam of wavelength λ1, a second laser that emits a laser beam of wavelength λ2, and a nonlinear optical crystal that receives the laser beam of wavelength λ1 and the laser beam of wavelength λ2 and outputs a coherent light beam of wavelength λ3 of the sum frequency in the relationship 1/λ1 +1/λ2 =1/λ3. The wavelength λ3 of the sum frequency is 589.3±2 nm corresponding to the sodium D line.

Hiroyuki Suzuki

Papers

Directional lasing oscillation of two-dimensional organic photonic crystal lasers at several photonic band gaps

Lasing action due to the two-dimensional quasiperiodicity of photonic quasicrystals with a Penrose lattice

Multiple quasi-phase-matched LiNbO3 wavelength converter with a continuously phase-modulated domain structure.

Organic light-emitting materials and devices for optical communication technology

Laser light source