Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the functi...

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation.

g-C3N4/carbon dot-based nanocomposites serve as efficacious photocatalysts for environmental purification and energy generation: A review

In this review, we survey the recent advances in nonlinear optics and the applications of two-dimensional (2D) materials. We briefly cover the key developments pertaining to research in the nonlinear optics of graphene, the quintessential 2D material. Subsequently, we discuss the linear and nonlinear optical properties of several other 2D layered materials, including transition metal chalcogenides, black phosphorus, hexagonal boron nitride, perovskites, and topological insulators, as well as the recent progress in hybrid nanostructures containing 2D materials, such as composites with dyes, plasmonic particles, 2D crystals, and silicon integrated structures. Finally, we highlight a few representative current applications of 2D materials to photonic and optoelectronic devices.

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Nonlinear optical properties and applications of 2D materials: theoretical and experimental aspects

Metal nanoparticles (MNPs) hold great technological promise because of the possibility of engineering their electronic and optical properties through material design. One of the effective methods to fabricate MNPs is ion implantation. In this review, recent results on the nonlinear optical properties of nanoparticles (including copper, silver, gold, and bismuth nanoparticles) doped in various bases have been discussed. Some specific optical nonlinear properties, such as nonlinear refraction, two-photon absorption, and optical limiting, for femtosecond, picosecond, and nanosecond laser pulses have also been covered. In addition to ion implantation, we have summarized several other methods for the preparation of composite materials, and Z-scan has been used to study the nonlinear optical properties of these materials.

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Nonlinear optical properties of metal nanoparticles: a review

A new organic nonlinear optical single crystal, isonicotinamide bis-paminobenzoic acid (INBAB), is grown from methanol solution using a slow evaporation solution technique. INBAB belongs to a monoclinic system with the space group P21/n. Its relative optical transmittance and optical band gap are found to be 58% and 3.4 eV, respectively. INBAB is thermally stable up to 147°C. The laser-induced surface damage threshold for our crystal is equal to 1.2 GW/cm for the 1064 nm Nd:YAG laser radiation. The nonlinear refractive index, the absorption coefficient and the third-order nonlinear susceptibility of our crystal are determined using a Z-scan technique. The material demonstrates optical-limiting behaviour up to the input irradiance of around 5.63 mW.

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Structure and characterization of a new organic crystal for optical limiting applications, isonicotinamide bis-p-aminobenzoic acid

The Sr1.95Ba0.05 CeO4:Eu3+ phosphors are synthesized by the solid-state reaction method. The samples are characterized using X-ray diffraction (XRD), diffuse reflectance spectroscopy and photoluminescence (PL) spectra. The XRD results reveal that the synthesized phosphors are genuine crystalline and belong to the orthorhombic structure. The intense PL emission is optimized from the PL spectra at various doping concentrations of europium ions. The results indicates that the phosphor can be effectively excited under 264 nm wavelength producing on intense emission spectrum of the synthesis material at 484 nm (blue region). The color purity of the phosphor is confirmed by CIE coordinates (x = 0.217, y = 0.265). The experimental data indicate that the prepared phosphors can be used as blue-emitting material in the field of illuminations and display devices.

Synthesis, photoluminescence properties of Sr1.95Ba0.05CeO4:Eu3+ for LED applications

Synthesis, crystal growth, structural, spectral, thermal, optical characteristics and density functional theory calculations of a novel third-order nonlinear optical material: 4-acetylanilinium dihydrogen phosphate (4AADP) single crystals

The SrLa2−xO4:xEu3+ phosphors are synthesized through high-temperature solid-state reaction method at 1473 K with various doping concentration. Their phase structures, absorption spectra, and luminescence properties are investigated by X-ray diffraction (XRD), UV–Vis spectrophotometer and photoluminescence spectrometry. The intense absorption of SrLa2−xO4:xEu3+ phosphors have occurred around 400 nm. The prominent luminescence spectra of the prepared phosphors exhibited bright red emission at 626 nm. The doping concentration 0.12 mol% of Eu3+ is shown to be optimal for prominent red emission and chromaticity coordinates are x = 0.692, y = 0.3072. Considering the high colour purity and appropriate emission intensity of Eu3+ doped SrLa2O4 can be used as red phosphors for white light emitting diodes (WLEDs).

G. Vinitha

Papers

Structure and characterization of a new organic crystal for optical limiting applications, isonicotinamide bis-p-aminobenzoic acid

Synthesis, photoluminescence properties of Sr1.95Ba0.05CeO4:Eu3+ for LED applications

Synthesis, crystal growth, structural, spectral, thermal, optical characteristics and density functional theory calculations of a novel third-order nonlinear optical material: 4-acetylanilinium dihydrogen phosphate (4AADP) single crystals

Optical properties of Eu3+ activated SrLa2O4 red-emitting phosphors for WLED applications

Structural, Spectral, Electrical and Nonlinear Optical Characterizations of rGO-PANI Composites