Alvaro Blanco

• Physics
• Researcher at Spanish National Research Council

Colloidal photonic crystals, or artificial opals, derive their unique optical properties from the periodic arrangement of their constituent particles. Central to the functionality of these materials is the precise control...

By preparing colloidal crystals with random missing scatterers, crystals are created where disorder is embodied as vacancies in an otherwise perfect lattice. In this special system, there is a critical defect concentration where light propagation undergoes a transition from an all but perfect reflector (for the spectral range defined by the Bragg c...

Colloidal suspensions crystallize by a natural sedimentation process under certain conditions, the initial volume fraction being one of the parameters that govern this process. Here, we have developed a simple in-situ, real-time, optical characterization technique to study silica colloidal suspensions during natural sedimentation in order to shed n...

Passive daytime radiative cooling has recently become an attractive approach to address the global energy demand associated with modern refrigeration technologies. One technique to increase the radiative cooling performance is to engineer the surface of a polar dielectric material to enhance its emittance at wavelengths in the atmospheric infrared...

Complex systems involving networks have attracted strong multidisciplinary attention since they are predicted to sustain fascinating phase transitions in the proximity of the percolation threshold. Developing stable and compact archetypes that allow one to experimentally study physical properties around the percolation threshold remains a major cha...

High-index dielectric nanostructures have emerged as an appealing complement to plasmonic nanostructures, offering similar light management capabilities at the nanoscale but free from the inherent optical losses. Despite the great interest in these all-dielectric architectures, their fabrication still requires cumbersome fabrication techniques that...

Silicon‐based materials are needed in cutting‐edge technological fields, for which hierarchical porosity and photonic properties help improve performance. In this work, the versatility of several fabrication routes that combine silicon infiltration by chemical vapor deposition (CVD), reactive ion etching (RIE), and carbon calcination, which produce...

The regulation of temperature is a major energy‐consuming process of humankind. Today, around 15% of the global‐energy consumption is dedicated to refrigeration and this figure is predicted to triple by 2050, thus linking global warming and cooling needs in a worrying negative feedback‐loop. Here, an inexpensive solution is proposed to this challen...

The regulation of temperature at the macro and microscale is a major energy-consuming process of humankind. Modern cooling systems account for 15% of the global energy consumption and are responsible for 10% of greenhouse gas emissions. Due to global warming, a ten-fold growth in the demand of cooling technologies is expected in the next 30 years,...

Mesoscale self-assembly of particles into supercrystals is important for the design of functional materials such as photonic and plasmonic crystals. However, while much progress has been made in self-assembling supercrystals adopting diverse lattices and using different types of particles, controlling their growth orientation on surfaces has receiv...

The photonic properties of 3D colloidal crystals made of Stöber silica spheres are shown to significantly depend on the relative humidity of the environment. The photonic bandgap of bare artificial opals formed by hydrophilic silica markedly varies in humid air along the entire range of water vapor concentration without the need for infiltration of...

Hierarchically porous carbon holds promise for many applications involving not only electrical, catalytic, power storage and related functionalities but, despite absorption in the visible and near-infrared, also optical and sensing uses are envisaged. In this paper, the self-assembly of heterogeneous core–shell and hollow carbon spheres based on po...

The photonic properties of artificial opals directly depend on the atmosphere (air, usually) filling the voids in the constitutive dielectric material. Here, a novel use of bare artificial silica opals (direct and inverse) is presented for straightforward water dew detection, in which the stop‐band exhibits a drastic change upon soaking of the void...

Self-assembly of particles into long-range, three-dimensional, ordered superstructures is crucial for the design of a variety of materials, including plasmonic sensing materials, energy or gas storage systems, catalysts and photonic crystals. Here, we have combined experimental and simulation data to show that truncated rhombic dodecahedral particl...

Biopolymer-based composites enable to combine different functionalities using renewable materials and cost-effective routes. Here we fabricate novel thermoresponsive photonic films combining cellulose nanocrystals (CNCs) with a polydiolcitrate elastomer exhibiting shape memory properties, known as hydroxyl-dominant poly(dodecanediol-co-citrate) (PD...

A method to produce photonic glasses (disordered dielectric structures built from monodisperse spheres) composed of silica is discussed. This method is capable of dispensing samples in a few minutes with the help of a uniaxial press. An analytical model that accounts for the most relevant features and explains how Mie scattering is the leading phen...

Intensity fluctuations in lasers are commonly studied above threshold in some special configurations (especially when emission is fed back into the cavity or when two lasers are coupled) and related with their chaotic behaviour. Similar fluctuating instabilities are usually observed in random lasers, which are open systems with plenty of quasi-mode...

On page 4357, C. López and co-workers perform a profuse and systematic study of factors affecting the hydrothermal synthesis of carbon spheres on polystyrene seeds. This green reaction allows the synthesis of hybrid polystyrene-carbon spheres monodisperse to below 5% with no-aggregation, in a size range between 500 and 900 nm (the range of interest...

The understanding of how the arrangement of defects in photonic crystals impacts its photonic properties is cru-cial for the design of functional materials based thereon. By preparing photonic crystals with random missing scatterers we create crystals where disorder is embodied as vacancies in an otherwise perfect lattice rather than the usual posi...

A photonic glass composed of monodisperse silica spheres is stepwise infiltrated with additional conformal layers of silica, by using chemical vapor deposition. It is shown that for a small infiltration degree, the resonant features of the glass are preserved. The possibility of modifying the light-transport mean free path in the sample is further...

Photonics glasses (PGs) are materials composed of monodisperse spherical particles which exhibit resonant behavior regarding their interaction with light. By stepwise infiltrating them with conformal layers of silica, Á. Blanco and co-workers show on page 352 that their transparency may be further tailored and demonstrate a significant change on th...

Monodisperse carbon spheres between 500 and 900 nm are hydrothermally synthesized from glucose on polystyrene seeds. Control over temperature, time, glucose concentration, and seed size yields hybrid spheres without aggregation and no additional spheres population. Pyrolysis transforms the hybrid into hollow carbon spheres preserving monodispersity...

Solid colloidal ensembles inherently contain water adsorbed from the ambient moisture. This water, confined in the porous network formed by the building submicron spheres, greatly affects the ensemble properties. Inversely, one can benefit from such influence on collective features to explore the water behavior in such nanoconfinements. Recently, n...

Shape-memory composites may be used as advanced photonic white paints to manipulate the transport of light. On page 1080, M. C. Serrano, A. Blanco, and co-workers show how they can perform as shape-configurable active media when doped with an organic dye, able to sustain non-resonant feedback random lasing. Photoluminescence may be used to monitor...

Water in colloidal crystals, usually adsorbed from surrounding moisture, significantly affects their properties but also gives clues to general liquid-interface nanoscale phenomena. The unique features of colloidal crystals (as ordered, photonic structures) allow novel approaches for the study of nanoconfined water, which sometimes builds intriguin...

Water on solid surfaces is ubiquitously found in nature, in most cases due to mere adsorption from ambient moisture. Because porous structures have large surfaces, water may significantly affect their characteristics. This is particularly obvious in systems formed by separate particles, whose interactions are strongly influenced by small amounts of...

Although enormous advances are accomplished using shape memory polymers (SMPs) and their derived composites, the application of these media in optics and photonics is still restricted to a few systems. The present work addresses the fabrication and characterization of novel composites based on polydiolcitrates doped with titania nanoparticles, aimi...

Novel photonic nanostructures with thermoresponsive shape-memory properties are presented. These materials, synthesized by imprinting a surface nanopattern on shape-memory polydiolcitrate elastomers, incorporate programmable optical properties that can be modulated or temporary erased by external stimuli. The multifunctional nature of these materia...

Photonic systems with the capability to respond to different stimuli are more and more desirable for achieving multifunctionality and higher levels of performance. They demand materials with responsivity that may eventually be used for integrating sensing and actuating functions, a feature highly pursued in technological applications. A notable pro...

We show a simple method to visualize the morphology of water adsorbed within the pore network of colloidal crystals made of submicrometer silica spheres. Water is replicated into silica by modified silicon tetrachloride hydrolysation under standard ambient conditions, making it visible to standard electronic microscopy and thus allowing one to disc...

Fast and reversible photonic-bandgap tunability is achieved in silica artificial opals by local heating. The effect is fully reversed as is heat rapidly dissipates through the non-irradiated structure without active cooling, and water is readsorbed. The performance is strongly enhanced by decreasing the photoirradiated opal volume, allowing bandgap...

We apply a recent optical technique to investigate fundamental water adsorption/desorption phenomena on submicrometer Stöber silica sphere surfaces of varying hydrophilicity. Thermally annealed (partially dehydroxylated) silica colloidal crystals are used as test systems for the sensitivity of their photonic properties to water. The allocation of p...

Composite materials consisting of a monolayer of polystyrene spheres (diameters of 430 and 520 nm) and porous silica, filling in the interstices, have been fabricated and characterized. The proposed growth method introduces some novelties as far as the fabrication of this kind of monolayers is concerned, as it probes the compatibility of coassembly...

Here we show the suitability of nanoindentation to study in detail the micromechanical response of silica colloidal crystals (CCs). The sensitivity to displacements smaller than the submicrometer spheres size, even resolving discrete events and superficial features, revealed particulate features with analogies to atomic crystals. Significant robust...

Hybrid metallodielectric systems where dielectric components are combined with metals supporting surface plasmons are able to spatially redistribute the electromagnetic field intensity within its volume through hybrid photonic-plasmonic modes. While most of the work done recently in this kind of systems has been focused on the way such redistributi...

Many modern systems are based on photoresponsive materials, in which properties such as the refractive index need to be effectively controlled. An extensively used means of achieving this is to photoinduce birefringence by alignment of anisotropic azochromophores via light-induced isomerization. However, the refractive index changes are typically s...

Physisorbed and structurally bound (surface and internal) water in silica opals are distinguished and quantified by thermogravimetry. By controlled dehydroxylation with thermal annealing, we correlate these forms of water with the silica chemistry. In particular, we find that the silica capability to physically adsorb water from ambient moisture ex...

3D-nanostructured ensembles of silicon nanocrystals forming inverse opals, directly prepared by magnesioreduction, exhibited intense photoluminescence in a broadband range (visible and NIR). Light emission, which strongly diminished under photoexcitation, was preserved by engineering the nanocrystals interface with atomic layer deposition of alumin...

In this work, we present a study of the typical spontaneous defects present in self-assembled colloidal monolayers grown from polystyrene and silica microspheres. The quality of two-dimensional crystals from different colloidal suspensions of beads around 1 μm in diameter has been studied qualitatively and quantitatively, evaluated in 2D hexagonal...

In this letter, we present both experimental and numerical studies of the magneto-optical (MO) properties of nickel infiltrated opals. Ni can show interesting MO properties that can be controlled by nanostructuration through colloidal crystals templating. Nanostructuration allows the coupling of light to surface plasmon modes of Ni, and a clear dep...

We report on an extremely fast and versatile synthetic approach, based on microwave assisted sol-gel chemistry, that allows a conformal nanometric coating of intricate three-dimensional structures. Using this methodology, we have achieved a conformal coverage of large areas of three-dimensional opals with a superparamagnetic manganese ferrite layer...

Some characteristics of silica--based structures-like the photonic properties of artificial opals formed by silica spheres--can be greatly affected by the presence of adsorbed water. The reversible modification of the water content of an opal is investigated here by moderate heating (below 300 °C) and measuring in situ the changes in the photonic b...

Hybrid self-assembled metallodielectric structures have been recently explored as a means to strongly modify the spontaneous emission of internal sources. In this work we explore the role of losses on their optical response.

The emission properties of two-dimensional self-assembled photonic-plasmonic crystals are fine tuned by varying the filling fraction for a monolayer of dye-doped polystyrene spheres on gold substrate. A complete experimental and theoretical study is presented.

Three-dimensional magnetophotonic crystals (3D-MPCs) are being postulated as appropriate platforms to tailor the magneto-optical spectral response of magnetic materials and to incorporate this functionality in a new generation of optical devices. By infiltrating self-assembled inverse opal structures with monodisperse nickel nanoparticles we have f...

The optical properties of two-dimensional hybrid photonic-plasmonic crystals are fine-tuned by modifying the dielectric component of the system. The filling fraction of the dielectric component in monolayers of spheres deposited on gold substrates is controlled by means of oxygen-plasma etching. Doing so enables spectral tuning of the optical modes...

Photonic crystals have proven their potential and are nowadays a familiar concept. They have been approached from many scientific and technological flanks. Among the many techniques devised to implement this technology self-assembly has always been one of great popularity surely due to its ease of access and the richness of results offered. Self-as...

A hybrid photonic-plasmonic crystal structure comprising a close-packed monolayer of dielectric spheres deposited on plasmon-supporting gold substrate is investigated. The spontaneous emission of organic dyes embedded in the beads experiences a strong modification in intensity, polarization, and directionality. These facts are accounted for conside...

Monodisperse colloids have been prepared efficiently by copolymerization of methyl methacrylate and fluorescent first- and second-generation poly(phenylenevinylene) dendrons under surfactant-free emulsion polymerization conditions. The copolymers were characterized by UV–vis and fluorescence spectroscopy and size exclusion chromatography. Transmiss...

We report here on the fabrication and characterization of magnetophotonic crystals obtained by infiltrating magnetic nanoparticles (maghemite) into silica-based inverse opals. Good quality opals, with adjustable photonic and magnetic characteristics have been obtained by this method. Magnetic and magneto-optic measurements, performed by using SQUID...

A random laser is a system formed by a random assembly of elastic scatters dispersed into an optical gain medium. We consider the case where the scattering is resonant. Our system, a photonic glass, can sustain scattering resonances over the gain frequency window, since it is formed by equal shape and equal size particles (monodisperse spheres) of...

A random laser is a system formed by a random assembly of elastic scatterers dispersed into an optical gain medium1. The multiple light scattering replaces the standard optical cavity of traditional lasers and the interplay between gain and scattering determines the lasing properties. All random lasers studied to date have consisted of irregularly...

In this work we report about the preparation and optical characterization of technologically relevant silver based nanostructures by metal infiltration of monolayered or opal-like templates of polystyrene (PS) latex spheres. Low toxicity electrolytic baths present obvious advantages and facilitate the synthesis, and are therefore, desirable methods...

In this Letter we demonstrate Mie resonances mediated transport of light in randomly arranged, monodisperse dielectric spheres packed at high filling fractions. By means of both static and dynamic optical experiments we show resonant behavior in the key transport parameters and, in particular, we find that the energy transport velocity, which is lo...

The realization of photonic glasses, solid random distributions of monodisperse spheres, which are a new photonic material was investigated. Thin disordered films was grown by combining a binary colloidal suspension composed by polymethyl metacrylate (PMMA) and polystyrene (PS) spheres. Few methods were tested to get a completely disordered arrange...

We present an optical characterization of photonic glasses, composed of randomly arranged, monodisperse dielectric spheres packed at high filling fractions. We provide a detailed optical study of the resonant behavior of diffuse light transport through such systems. By means of independent static and dynamic measurements, we show resonances in the...

Here we present the first observation of random lasing from a disordered assembly of monodisperse dielectric spheres. Laser mode competition is observed due to the resonant transport of Mie modes.

In this work we present both experimental and numerical studies of the optical properties of artificial opals. The staking of up to four layers of spheres may arise according to three different arrangements: face-centered cubic, hexagonal close-packed or double hexagonal close-packed. Our study shows that the transmission spectra features are chara...

The authors present a novel photonic material dubbed photonic glass, which is a solid, disordered, macroscopic assembly of monodisperse dielectric spheres. These spheres, whose diameter is of the order of the wavelength of the light, support Mie resonances and, as a result of a collective effect of these resonances, the photonic glass is expected t...

In this letter the authors present both experimental and numerical studies of the optical properties of four-layer artificial opals. The stacking of four layers of spheres may arise according to three different arrangements: face-centered cubic, hexagonal close packed, or double hexagonal close packed. The study shows that the transmission spectra...

In this letter the authors present both experimental and numerical studies of the optical properties of four-layer artificial opals. The stacking of four layers of spheres may arise according to three different arrangements: face-centered cubic, hexagonal close packed, or double hexagonal close packed. The study shows that the transmission spectra...

Photonics is the technology of photons (as electronics is the technology of electrons) and promises to be the new century's driving force in the advancement of, mainly but not only, communications and computing, the information technology. This technology was initiated with the advent of lasers and optical fibers which, for various reasons, embody...

Silicon and zinc oxide are two materials of great importance in photonics whose infiltration in opal templates has demonstrated the potential of both the materials and the templating technique. We describe the infiltration in organic opals made of polystyrene and the optical properties derived from the materials under the morphology imposed by the...

A large-area, high-quality, new composite materials obtained by structuring a ZnO inverted opal with colloidal CdTe nanocrystals in two steps of hierarchical colloidal self-assembly was reported. The fabrication is performed by an accurate infiltration in two hierarchical steps of colloidal self-assembly and the method of infiltrating a ZnO matrix...

A method to infiltrate silicon in polymeric self-assembled microstructure, that permits the building up of multi-layered structures arranged in 3D with photonic crystal optical response, by combining silica and silicon CVD processes, is discussed. The use of silica CVD permits a fine control over the degree of infiltration in polymer opals which ca...

The silica chemical vapor deposition (CVD) technique that allows not only silicon infiltration in polymer 3D templates but also finer tuning of their photonic crystal properties was investigated. By means of silica CVD it is possible to finely control the degree of infiltration in polymer opals, which can be used to degenerate a novel topology cons...

Silicon concentric layers enclosing spherical air cavities is one of the novel topologies created by the method of infiltrating silicon into polymeric self‐assembled microstructures. It is shown that by combining silica and silicon CVD it is possible to build up 3D arrangements of multilayered structures (see figure) with a photonic crystal optical...

We have shown that the combination of two complementary and compatible techniques, namely holographic lithography and Laser Direct Writing, allows the rapid, flexible and cheap fabri- cation of 3D PhC templates as well as the controlled incorporation of defects and waveguides. The optical transmission and reflection spectra of these structures in t...

Silicon and zinc oxide are two materials of great importance in photonics whose infiltration in opal templates has demonstrated the potential of both the materials and the templating technique. We describe the infiltration in organic opals made of polystyrene and the optical properties derived from the materials under the morphology imposed by the...

Zinc oxide (ZnO) was grown in synthetic opals by using chemical vapor deposition (CVD) method. The CVD method yielded large area, high quality ZnO-polystyrene (PS) and ZnO inverse opals, with very precise control of degree of infiltration. ZnO was grown in thin PS opal films on silicon substrates, using a diluted solution of DMZn in hexane as zinc...

We review our work on fabricating templates for photonic band gap materials at telecommunication wavelengths via holography and direct laser writing. Measured optical spectra are compared with theory, revealing the excellent quality of these structures.

Three-dimensional arrays of SiO2 nanometer particles lead to Bragg diffraction effects of visible light—as seen for natural opals, see also this issue's cover—and applications such as photonic bandgap materials. Teh fabrication of the opalline structures is described and details are given of how to obtain ordered compacts. The Figure shows a fractu...

We review our work on two complementary and compatible techniques, namely direct laser writing and holographic lithography which are suitable for fabricating three-dimensional Photonic Crystal templates for the visible and near-infrared. The structures are characterized by electron micrographs and by optical spectroscopy, revealing their high optic...

We present our work on the fabrication of three-dimensional Photonic Crystal templates by holographic lithography and direct laser writing. Both optical methods are highly qualified for the production of top-quality polymeric three-dimensional Photonic Crystals and allow in combination the controlled incorporation of defects and waveguides in large...

We fabricate three-dimensional photoresist templates by means of laser holography. In particular, fcc structures are achieved by placing a specially designed ``prism'' onto the photoresist surface. This solves the problem of previous work, in which the refraction at the air-photoresist interface made it impossible to obtain the required angles of t...

An optical study of the band structure of both silicon–silica composite and silicon inverse opals is presented. The study is aimed at demonstrating the development of a full photonic band gap for a system already revealed as paradigmatic. The characterization is based on the comparison between the band structure calculations and optical reflectance...

Full-text of this article is not available in this e-prints service. This article was originally published [following peer-review] in Journal de Physique IV, published by and copyright EDP Sciences. We describe the use of novel MOCVD methods designed to infill templated structures based upon synthetic opals in order to provide increased refractive...

Here we report different simple and inexpensive approaches to the fabrication of inverse opals originated from silica opal templates with sphere size in the range between 0.2 and 1.3 μm. The opal porous lattice is infiltrated with semiconductors (CdS, Ge, Si) as well as polymers by several methods such as chemical vapour deposition, chemical bath d...

Silica opals are used as templates where CdS is infiltrated with the aim to build inverse structures with enhanced photonic band gap properties. A control on the degree of infiltration, from 0% to 100%, is attained. The band gap at L is studied finding that the width decreases and then recovers as a function of CdS infilling (from bare opal to full...

Here we report on different approaches to the fabrication, characterization, and modelling of inverse opals. We start from Here we report on different approaches to the fabrication, characterization, and modelling of inverse opals. We start from silica opal templates with sphere size in the range between 0.2 μm and 1.3 μm. The opal porous lattice i...

CdS/opal photonic materials have been characterised by transmission electron microscopy. The photonic properties of opals formed by SiO2 nanospheres 380 nm in diameter, face-centred cubic ordered and with different CdS filling factors were studied by means of specular reflectance or transmission spectroscopy. It is shown that CdS semiconductor grow...

Photonic technology, using light instead of electrons as the information carrier, is increasingly replacing electronics in communication and information management systems. Microscopic light manipulation, for this purpose, is achievable through photonic bandgap materials, a special class of photonic crystals in which three-dimensional, periodic die...

We present in this paper the use of silica-coating for nanostructuring metal and semiconductor nanoparticles. The basic concept is the strict tailoring of the interparticle spacing through the thickness of the silica shell. Three different experiments are presented that exemplify this concept. The first example consists of the preparation of thin f...

We discuss photonic crystal properties of semiconductor-opal composites and explore the possibility of using these structures as photonic bandgap (PEG) materials in the visible and near-infrared region of the spectrum. Integrated reflectance in the optical region is used to show that the photonic crystal behavior of InP opal is enhanced with respec...

In this study we inspect the possibilities of using photonic crystals and, in particular, opal structures as hosts for active materials with the view to achieve laser action in solid state devices. We then show our recent work in the characterization of both the opal structure as a host and an active material. Our characterization of the opal is do...

In this work we propose and demonstrate a solution to the problems which arise when SiO2 monodisperse nanospheres of diameters under 300 nm or over 550 nm are used to obtain opal-based photonic crystals. If the nanospheres are too small, the sedimentation rate is very slow or even may not occur; if they are large enough, no significant order can be...

Here we present experimental evidence of the strong modification of the CdS photoluminescence when it is embedded in a SiO2 colloidal photonic crystal. When the emitted light matches a forbidden photonic band in the matrix, inhibition of the semiconductor photoluminescence is achieved. In this work we prove the effective control of this effect by m...

Atmospheric pressure metal-organic chemical-vapour deposition has been used to infill the voids within synthetic opals with InP in an attempt to modify the natural photonic behaviour of these materials. The process has been optimised to increase the semiconductor loading. By increasing the extent of InP infill within the voids, which in turn increa...

Control of the optical properties of SiO2 colloidal photonic crystals through thermal treatment is reported. The optical properties, studied by light transmission and reflection, are shown to vary through structural and physicochemical modification of the material, without loss of order. The Figure is a scanning electron micrograph of the fee cryst...

In this letter, we investigate the optical properties of packed monodisperse silica submicron spheres by means of optical transmission measurements. The results are compatible with a three dimensional face centered cubic order in these solid structures. The lattice parameter of these structures, and therefore their optical properties, can be easily...