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The topic of cholesteric-liquid-crystal lasers is a rapidly expanding research area in the field of soft-matter photonics. The increasing interest in this field is due to the high versatility that these lasers may possibly present and the prospects of giving rise to new miniaturized devices. However, further improvements in their operation capabilities are still required for potential applications. In this paper, we critically analyze the main strategies proposed up to now to optimize their performance. We show theoretically and experimentally that possible innovations in the device structure cannot produce lasers with threshold energies below a certain limit. This limit is determined by the light scattering and absorption losses inside the liquid crystal. Even assuming the case of samples free of defects and perfectly non-absorbing, an intrinsic light scattering, typical of mesogens, still remains. Numerical estimates of the thresholds indicate that these lasers could hardly be driven by compact light sources such as current electroluminescent or light-emitting diodes. Since the improvement possibilities regarding cell architecture seem to be exhausted, the advance must come from the use of new dye molecules. These molecules should show enhanced emission cross-sections and be efficiently integrable within the mesogenic solvent. In addition, the fluorescent systems must present very small quantum yields to triplet states if continuous-wave lasing is sought. In this respect, quantum dots are an alternative to explore for further investigations.

Light upconversion by triplet-triplet annihilation (TTA-UC) in nanoparticles has received considerable attention for bioimaging and light activation of prodrugs. However, the mechanism of TTA-UC is inherently sensitive for quenching by molecular oxygen. A potential oxygen protection strategy is the coating of TTA-UC nanoparticles with a layer of oxygen-impermeable material. In this work, we explore if (organo)silica can fulfill this protecting role. Three synthesis routes are described for preparing water-dispersible (organo)silica-coated red-to-blue upconverting liposomes. Their upconversion properties are investigated in solution and in A549 lung carcinoma cells. Although it was found that the silica offered no protection from oxygen in solution and after uptake in A549 cancer cells, upon drying of the silica-coated liposome dispersion in an excess of (organo)silica precursor, interesting liposome-silica nanocomposite materials were obtained that were capable of generating blue light upon red light excitation in air.

Responsive polymer-based materials have found numerous applications due to their ease of synthesis and the variety of stimuli that they can be made responsive to. In this review, we highlight the group’s efforts utilizing thermoresponsive poly (N-isopropylacrylamide) (pNIPAm) microgel-based optical devices for various sensing and biosensing applications.

Poly (N-isopropylacrylamide) (pNIPAm)-based hydrogels and hydrogel particles (microgels) have been extensively studied since their discovery a number of decades ago. While their utility seems to have no limit, this feature article is focused on their development and application for sensing small molecules, macromolecules, and biomolecules. We highlight hydrogel/microgel-based photonic materials that have order in one, two, or three dimensions, which exhibit optical properties that depend on the presence and concentration of various analytes. A particular focus is put on one-dimensional materials developed in the Serpe Group.

Light-induced photoluminescence (PL) switching using azobenzene-doped liquid crystal (LC)-dispersed quantum dots (QDs) is demonstrated in a format of LC cell and LC-infiltrated tube. Before light irradiation, excitation photons undergo multiple scattering events before emission out of the LC cell, and PL intensity is high. Upon the light irradiation, the trans-to-cis photoisomerization of azobenzene makes the QD-dispersed LCs highly transparent, thus allowing most excitation photons to pass through LCs and decrease PL intensity. This demonstration may allow a new modulating technique for future development of light-switchable, QD-emission-based display or photonic devices.

We demonstrate the fabrication and use of a 10-cm-long-PMMA microwire with ultrahigh waveguide nonlinearity γ= 176 W-1 m-1 that is fully compatible with standard single-mode silica fibers. The fabrication of this microtaper is simplified with respect to a previous approach as the core is made of a bulk cylinder rather than a single-mode step-index fiber. The successful operation of this nonlinear component is demonstrated with a Kerr-shutter switching experiment based on nonlinear polarization rotation.

High value material including phosphates can result from: (i) major efforts to maintain and possible improve the quality of education, (ii) cross disciplinary approach (Chemistry, Physics, Geology, Biology etc.), (iii) implementation of new concepts which are able to push back the technological frontiers. In this context four examples of high value phosphate materials are analyzed in detail in this publication: • LaPO4 composites used at high temperatures and in oxygenated environment. • Cement for cold areas, • Phosphate Materials for inertial confinement fusion, • Photonic component for permanent storage of information. In all the previous examples the creation of new materials results from an overlapping between the basic functions of the phosphate groups and the new concepts related to various scientific fields e.g. electrochemistry, optics, mechanics, etc., and/or the use of new technologies to the elaboration of materials. The result is a representation of phosphate materials completely new compared to traditional views.

Nanoparticles exhibiting zero backscattering but a large scattering cross section in the forward direction should play a key role as light diffracting elements in photonic devices like solar cells. Using Mie theory we address lossless dielectric spheres that were recently reported to possess a magnetodielectric response to the illuminating wave, and analyze their scattering cross section together with their zero-backwards scattering conditions. We show that there is an optimum particle refractive index (m = 2.47), which yields maximum forward scattering without backwards scattering of light., Work supported by the Ministerio de Economia y Competitividad of Spain through grants FIS2012-36113-C03-03 and FIS2014-55563-REDC, and by the Comunidad de Madrid P2009/TIC-1476. J J S acknowledges an Ikerbasque Visiting Fellowship.

International audience; In this work, the overall point of interest is the occurrence of artefacts associated with dry etching processes on InP-based structures. By artefacts we mean creation of defects in the remaining material after etching, defects which might be deleterious to both performance of the photonic devices being fabricated, and reliability/lifetime of these devices. A specific sample structure was defined on InP with InAsxP1 − x quantum wells (QWs). These QWs are buried within 1 μm from the surface, for maximum sensitivity to reactive species produced in the etch plasma, and are designed with a gradual As/P composition, such that the luminescence peak produced by each QW is clearly identified. These samples thus possess a “built-in” marker including its own scale. We focused on chemistries with chlorine (SiCl4/H2/Ar and Cl2/N2), implemented in an inductively coupled plasma reactor. With such chemistries, etch rates of 0.5 μm/min can be reached. The samples are not really etched, but just exposed shortly to the plasma for the interaction to take place. Actually, we just etch at most a few tens of nanometers. Characterisation was carried out by spectrally-resolved cathodo-luminescence and photo-luminescence. We also measured secondary ion mass spectrometry profiles, which revealed the penetration of chlorine into the samples. High resolution transmission electron microscopy was used, to probe the crystal quality. By comparing doped and un-doped samples, we show that the chlorine observed after exposure consists at least partly in Cl− ions. The other important observation is some mechanical compressive stress, which is also a consequence of the local concentration of Cl impurities after exposure to the plasma

Dye sensitised solar cells (DSCs) typically include a mesoporous titanium dioxide (TiO2) scaffold, sensitised with an adsorbed dye, as the main active element responsible for the photon absorption and charge separation functionalities. The sintering process employed in the TiO2 active layer fabrication plays a crucial role in the formation of the nanoparticle (NP) scaffold and hence in the performance of a dye sensitised solar cell, as it allows the particles to form efficient inter-crystalline electric contacts providing high electron conductivity. Furthermore, the DSC design requires a conductive transparent top electrode which is typically made of fluorinated stannic oxide. Here we report on a highly spatially resolved scanning electron microscopy study in conjunction with focussed ion beam milling and energy dispersive X-ray (EDX) mapping of the distribution of all relevant elements within a DSC subsequent to a classical sintering process in the range of 350°C-550°C. Additionally, the article provides quantitative results regarding the found Sn diffusion and its effect on efficiency confirmed via J-V measurements. The effective spatial resolution of the EDX studies was calculated by Monte Carlo simulations of the electron trajectories and X-ray emission region. This permits to construct a model for the migration of Sn from the transparent conductive oxide into the TiO2 scaffold, resulting in alterations in the composition of the complex system which has a direct effect on the DSC performance. J-V measurements conclude that sintering temperature of 500°C is close to the optimum regarding Sn diffusion enhancement of DSCs. Sintering temperatures above 500°C were causing a drop in the DSC efficiency and are therefore not recommended. In order to optimize the DSC efficiency, the results are summarized by a model that explains how the efficiency varies with the Sn diffusion process.

Optical materials and photonic structures based on rare earth ions are the cornerstone of the scientific and technological building where photonics and material science smartly cooperate to develop new physics, new devices, and new applications in both high-tech domain and daily use tools. These ancient but ever innovative kinds of materials are used to construct luminescent structures, which can perform sensing and functionalized structures to address successfully the main socio-economic challenges that we are facing in many fields, going from health care to security, from energy saving to efficient and clean industrial production, from environment protection to fast and efficient communications Photonics, with its pervasiveness, has already been identified as one of the Key Enabling Technologies in the XXI century, and through advanced research it can not only give a strong contribution to find new technical solutions to still unsolved problems, but it can also pave the way to applications that up to now are far from being imagined. The Workshop on Photoluminescence in Rare Earths: Photonic Materials and Devices (PRE) has the motivation to provide a platform for the above mentioned prospects.

The way FRET takes place in dye-doped biopolymer complexes is studied by time-resolved measurements. The efficiency of the energy transfer is controlled by the relative concentration of the donor/acceptor species and described with a distribution of processes. Amplified spontaneous emission in the system and its evolution with the FRET efficiency is monitored. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., This work was supported by the Spanish MINECO CSD2007-0046 (Nanolight.es) and MAT2012-31659 (SAMAP) projects; Comunidad de Madrid S2009/MAT-1756 (PHAMA) programme and EU Nanophotonics4Energy contract 248855. M. Ibisate acknowledges the MICINN Ramón y Cajal programme.

BACKGROUND: An aptamer based biosensor (aptasensor) was developed and evaluated for rapid colorimetric detection of Escherichia coli (E. coli) O157:H7. METHODOLOGY/PRINCIPAL FINDINGS: The aptasensor was assembled by modifying the truncated lipopolysaccharides (LPS)-binding aptamer on the surface of nanoscale polydiacetylene (PDA) vesicle using peptide bonding between the carboxyl group of the vesicle and the amine group of the aptamer. Molecular recognition between E. coli O157:H7 and aptamer at the interface of the vesicle lead to blue-red transition of PDA which was readily visible to the naked eyes and could be quantified by colorimetric responses (CR). Confocal laser scanning microscope (CLSM) and transmission electron microscopy (TEM) was used to confirm the specific interactions between the truncated aptamer and E. coli O157:H7. The aptasensor could detect cellular concentrations in a range of 10(4)~ 10(8) colony-forming units (CFU)/ml within 2 hours and its specificity was 100% for detection of E. coli O157:H7. Compared with the standard culture method, the correspondent rate was 98.5% for the detection of E. coli O157:H7 on 203 clinical fecal specimens with our aptasensor. CONCLUSIONS: The new aptasensor represents a significant advancement in detection capabilities based on the combination of nucleic acid aptamer with PDA vesicle, and offers a specific and convenient screening method for the detection of pathogenic bacteria. This technic could also be applied in areas from clinical analysis to biological terrorism defense, especially in low-resource settings.

In this paper, an experimental study is presented on Er:SiO 2 films prepared by an rf-cosputtering deposition technique, and then annealed in the 100–1200 °C range. Samples were characterized by spectrally resolved cathodoluminescence, UV–VIS photoluminescence and Rutherford Backscattering Spectrometry (RBS). Strong optical modifications with temperature were observed, connecting the peculiar features of the Er luminescence activity to those of the silica matrix, namely, the density of nonbridging oxygen hole centers, oxygen-deficient sites and OH groups. In general, a complex phenomenology was observed, involving major local rearrangements of the Er environment. RBS data allowed to evidence migration phenomena, resulting in a compositional change of the films, thus indicating the progressive modification of the system as well as the possible formation of Er nanoclusters for high temperatures.

BackgroundPhotonic crystals are artificial structures that have periodic dielectric components with different refractive indices. Under certain conditions, they abnormally refract the light, a phenomenon called negative refraction. Here we experimentally characterize negative refraction in a one dimensional photonic crystal structure; near the low frequency edge of the fourth photonic bandgap. We compare the experimental results with current theory and a theory based on the group velocity developed here. We also analytically derived the negative refraction correctness condition that gives the angular region where negative refraction occurs.Methodology/principal findingsBy using standard photonic techniques we experimentally determined the relationship between incidence and negative refraction angles and found the negative refraction range by applying the correctness condition. In order to compare both theories with experimental results an output refraction correction was utilized. The correction uses Snell's law and an effective refractive index based on two effective dielectric constants. We found good agreement between experiment and both theories in the negative refraction zone.Conclusions/significanceSince both theories and the experimental observations agreed well in the negative refraction region, we can use both negative refraction theories plus the output correction to predict negative refraction angles. This can be very useful from a practical point of view for space filtering applications such as a photonic demultiplexer or for sensing applications.

Silica-hafnia is a reliable and flexible binary system that has proved to be suitable for rare earth doping and fabrication of amorphous and glass-ceramic planar waveguides, as well as for improving thermal stability of spherical microresonators. Here we present a short overview on some rare earth - activated photonic structures fabricated by sol gel route. Fabrication protocols and structural, optical and spectroscopic assessment of the investigated systems are reported. In order to put in evidence the reliability and versatility of the silica-hafnia system for photonics applications, different examples of confined structures are discussed: i) SiO2 amorphous waveguides; ii) glass-ceramic waveguides fabricated by top-down and bottom-up approach; iii) coated spherical microresonators.

Special Issue: "Advanced Materials & Photonics Applications", publisher: SoftMotor Ltd (ISSN 1744-2400); International audience; Silica-hafnia is a reliable and flexible binary system that has proved to be suitable for rare earth doping and fabrication of amorphous and glass ceramic planar waveguides, as well as for improving thermal stability of spherical microresonators. Here we present a short overview on some rare earth - activated photonic structures fabricated by sol gel route. Fabrication protocols and structural, optical and spectroscopic assessment of the investigated systems are reported. In order to put in evidence the reliability and versatility of the silica-hafnia system for photonics applications, different examples of confined structures are discussed: i) SiO2 amorphous waveguides; ii) glass-ceramic waveguides fabricated by top-down and bottom-up approach; iii) coated spherical microresonators.

This PDF file contains the front matter associated with SPIE Proceedings Voume 7366, including Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing., SPIE Europe; GMM VDE/VDI Gesellschaft Mikroelektronik, Mikro- und Feinmechanik

In photonic materials the refractive index varies on a length scale comparable to the wavelength of light; as a consequence, propagation of light is strongly modified with respect to that in homogeneous dielectric materials. In this thesis experiments are reported with light souces in crystalline and random photonic materials. It had been predicted that photonic crystals could modify the radiative decay rate of embedded light sources. However, this prediction was never verified experimentally. We have been able to prove this prediction for the first time using CdSe nanocrystals as light sources in titania inverse opal photonic crystals. Spherical CdSe nanocrystals with a diameter between 3 nm and 6 nm were made by wet-chemical synthesis. These nanocrystals show so-called 'quantum-size-effects': the colour of the emission depends on the nanocrystals' size. Nanocrystals of 3 nm size emit blue light while nanocrystals of 6 nm emit red light. We measured the rate of emission, or the radiative lifetime, of the nanocrystals as a function of emission colour and observed that blue light is emitted about three times faster than red light. The rates were found to be in good agreement with quantum-mechanical calculations on small particles. Subsequently, we embedded the nanocrystals in our photonic crystals and again measured the radiative lifetime. We observed that the lifetime of the nanocrystals varied by a factor-of-three depending on the lattice parameter of the photonic crystal. With this we have confirmed the hypothesis that photonic crystals can indeed control the radiative lifetime of embedded light sources. Porous gallium phosphide (GaP) is a random photonic material that can be made by electrochemical etching of crystalline GaP. This process has been applied for many years. We observed that during etching light is generated at the pore fronts. We were able to reveal the mechanism of light generation and attributed it to a hot-carrier process. During etching a high electric field is required. As a consequence hot carriers are generated and these hot carriers give rise to emission. Besides exploration of the emission and its mechanism we were able to use the emission as an internal light source to measure the optical properties of porous GaP during electrochemical etching. This allows one to deduce the optical characteristics of porous GaP directly and over the complete visible range in a single experiment.

In photonic materials the refractive index varies on a length scale comparable to the wavelength of light; as a consequence, propagation of light is strongly modified with respect to that in homogeneous dielectric materials. In this thesis experiments are reported with light souces in crystalline and random photonic materials. It had been predicted that photonic crystals could modify the radiative decay rate of embedded light sources. However, this prediction was never verified experimentally. We have been able to prove this prediction for the first time using CdSe nanocrystals as light sources in titania inverse opal photonic crystals. Spherical CdSe nanocrystals with a diameter between 3 nm and 6 nm were made by wet-chemical synthesis. These nanocrystals show so-called 'quantum-size-effects': the colour of the emission depends on the nanocrystals' size. Nanocrystals of 3 nm size emit blue light while nanocrystals of 6 nm emit red light. We measured the rate of emission, or the radiative lifetime, of the nanocrystals as a function of emission colour and observed that blue light is emitted about three times faster than red light. The rates were found to be in good agreement with quantum-mechanical calculations on small particles. Subsequently, we embedded the nanocrystals in our photonic crystals and again measured the radiative lifetime. We observed that the lifetime of the nanocrystals varied by a factor-of-three depending on the lattice parameter of the photonic crystal. With this we have confirmed the hypothesis that photonic crystals can indeed control the radiative lifetime of embedded light sources. Porous gallium phosphide (GaP) is a random photonic material that can be made by electrochemical etching of crystalline GaP. This process has been applied for many years. We observed that during etching light is generated at the pore fronts. We were able to reveal the mechanism of light generation and attributed it to a hot-carrier process. During etching a high electric field is required. As a consequence hot carriers are generated and these hot carriers give rise to emission. Besides exploration of the emission and its mechanism we were able to use the emission as an internal light source to measure the optical properties of porous GaP during electrochemical etching. This allows one to deduce the optical characteristics of porous GaP directly and over the complete visible range in a single experiment.