Dye-doped Photonic Crystals Research Articles

Chameleon photonic crystals: Acid-induced emission and absorption shifts for sensor applications

Thanks to their optical properties, photonic crystals are a very interesting group of modern materials. Their applicability is further enhanced by the possibility of doping with stimuli-responsive compounds. This paper presents a preparation and characterization of photonic crystals doped with a luminescent dye – ethyl eosin. By doping with this dye, a material with sensor properties and unique optical properties such as angle-dependent emission was obtained. The study focused on determining the luminescence properties of the opals and the dye, specifically their quantum yield (QY). Moreover, the obtained dye-doped photonic crystals exhibit a rapid change in luminescence properties and color after contact with vapors of inorganic acids commonly used in industry. Furthermore, a three-dimensional opal doped with ethyl eosin exhibits a selective change in the presence of nitric acid(V), unlike the dye solution. These luminescent and sensing properties, coupled with reversibility, make this material fascinating.

Interplay of dual photonic stopband in fluorescence enhancement from dye-doped photonic crystal heterostructures

Photonic crystal (PhC) structures with appropriate characteristics are necessary to control spontaneous emission from fluorophores while designing miniaturized lasers. We report the fabrication and detailed studies on the emission features of two different spectrally engineered PhC heterostructures made from dye-doped opal and one-dimensional (1-D) multilayer stack. Our results demonstrate notable enhancements of emission from PhC heterostructure enabled by the stopband overlap of three-dimensional (3-D) opals and 1-D multilayers. In the presence of the 1-D multilayer, the distributed feedback from opals further enhances the emission from the dye. We emphasize the role of the interplay of the spectral overlap of stopbands and the band edges in the dye-doped PhC heterostructures to control their emission features. The emission results obtained from our heterostructures are very much dependent on the relative spectral position of the stopbands of the constituent 1-D and 3-D photonic crystals. Input pump energy-dependent emission results indicate that such heterostructures are potential candidates for designing colloidal PhC-based lasers.

Localized surface plasmon-influenced fluorescence decay in dye-doped metallo-dielectric opals

Well-ordered opaline photonic crystals are grown by inward growing self-assembly method from Rhodamine B dye-doped polystyrene colloids. Subsequent to self-assembly, the crystals are infiltrated with gold nanoparticles of 40 nm diameter. Measurements of the stopband features and photoluminescence intensity from these crystals are supplemented by fluorescence decay time analysis. The fluorescence decay times from the dye-doped photonic crystals before and after the infiltration are dramatically different from each other. A lowered fluorescence decay time was observed for the case of gold infiltrated crystal along with an enhanced emission intensity. Double-exponential decay nature of the fluorescence from the dye-doped crystal gets converted into single-exponential decay upon the infiltration of gold nanoparticles due to the resonant radiative process resulting from the overlap of the surface plasmon resonance with the emission spectrum. The influence of localized surface plasmon due to gold nanoparticles on the increase in emission intensity and decrease in decay time of the emitters is established.

Analysis of Lasing in Dye-Doped Photonic Crystals

Recently, we experimentally demonstrated room-temperature lasing of self-assembled opal photonic crystal (PhC) made of rhodamine-B-doped polystyrene colloids. Here, we explain this experimental observations by analyzing the phenomenon of light amplification in dye-activated PhCs via a complex-valued permittivity of the colloids. We show that the lasing is facilitated by the enhanced distributed feedback due to the reduced group velocity in the vicinity of the photonic band edge. This simple approach to the analysis of PhC lasing behavior allows us to calculate the lasing wavelength in close agreement with the experimental value. It also enables the estimation of gain coefficient required for lasing and may prove useful in design of compact PhC-based lasers.

Lasing in dye-doped photonic crystals at the edge of fluorescence band gaps

Based on holographic lithography, layered dye-doped photonic crystals are fabricated in dichromated gelatin emulsions. Under pumping of 532 nm pulse laser, fluorescence spectrums of samples show up remarkable band gaps, and lasing is achieved at the edge of fluorescence band gap with pumping energy increasing. Furthermore, the effects on lasing of matching between the edge of band gap and the peak of fluorescence are studied. Lasing threshold becomes lower as the edge of band gap is closer to the peak of fluorescence. Otherwise, it is difficult for lasing. The study provides new idea and method for the development of super low-threshold photonic crystal laser.

Spatial and spectral distributions of emission from dye-doped photonic crystals in reflection and transmission geometries

Spectral distribution of emission was measured in a large angular range (8 deg to 180 deg) around a self-assembled photonic crystal synthesized from colloids of Rhodamine-B dye-doped polystyrene. Its comparison with the emission from the same dye-doped colloids in a liquid suspension provides a better understanding of the anisotropic propagation of light within the structure due to its pseudo-gap properties. The spontaneous emission is suppressed by 40% in the presence of the stop band over a large bandwidth (∼50%) of the first-order bandgap in the ΓL direction, due to the appropriate choice of the colloidal diameter. Spectral shifts in the spontaneous emission spectrum occur with the variation in the detection angle. The inevitable disorder in the self-assembled crystals and the resultant effect on emission was modeled by comparing the experimentally obtained reflection spectrum with the band structure calculated using the Korringa-Kohn-Rostoker method to exclude finite-size effects. Reflection and transmission are complementary because of the absence of strong absorptive effects. The extent of redistribution in the emission from a photonic crystalline environment with respect to a homogeneous emitter is significant in the spectral and spatial domains.

Preparation of Monodisperse Dye-Doped Copolymer Spheres for Photonic Crystals

Monodisperse dye-doped copolymer spheres were prepared via a soap-free emulsion polymerization and swelling method. To study the relationship between the particle diameters and the optical properties of the dye-doped photonic crystals, monodisperse copolymer spheres with particle diameters varying from 581 to 98 nm were prepared. When melanin dye was doped into the spheres, it efficiently reduced the light scattering inside the crystals and eliminated the iridescent effect in the photonic crystal images. The results of this study are expected to provide useful information for the synthesis of monodisperse dye-doped copolymer spheres and applications involving photonic papers.

Low-Threshold Lasing in 3D Dye-Doped Photonic Crystals Derived from Colloidal Self-Assemblies

In this article, we demonstrated low-threshold lasing in three-dimensional (3D) polymeric photonic crystals derived from colloidal suspensions. To achieve this, we used monodisperse silica beads in a photocurable refractive index matched medium with high viscosity and polarity. In this system, the colloidal silica beads rapidly self-organized into nonclose-packed fcc crystals because of strong repulsive interparticle potential relative to diminishing van der Waals attraction, and subsequently the colloid crystals were solidified by UV irradiation. Dye molecules as optical gain medium were incorporated in the polymeric matrix by simply mixing the dye molecules and the photocurable suspension before casting the photonic crystal films. The translucent composite photonic films showed emission inhibition and enhancement due to the low photon density of states (DOS) at the stop band and high DOS at the band edge, respectively. On the other hand, the porous photonic films, which were prepared by removal of silica particles from the composite films, exhibited larger bandwidth and higher reflectivity (>80%) due to the enhanced refractive index contrast. Under irradiation of excitation light source, the porous photonic film showed strongly enhanced stimulated emission at the band edge by a factor of more than 300 with respect to the spontaneous emission of dye molecules embedded in a bulk film without nanostructure. In addition, the lasing wavelength could be controlled by simply changing the particle volume fraction in the composite films from which the porous films were prepared. Moreover, the threshold excitation intensity was reduced by a factor of one-tenth relative to the previously reported values. The simple method for preparing 3D photonic crystals described here and subsequent lasing characteristics have great potential in a broad range of applications including displays, μ-TAS, and optofluidic light sources.

Lasing from dye-doped photonic crystals with graded layers in dichromate gelatin emulsions

We report on optically pumped lasing from dye-doped, graded-spacing layer structures of dichromate gelatin emulsions fabricated using two-beam holographic interference. The graded layers exhibited deep and wide photonic band gaps. Multimode lasing with both a low threshold and a high quality factor was observed at the band edge of the photonic band gap. We modeled the emissions from the dye-doped graded layer system using a finite difference time domain technique and achieved good agreement with experimental results.