Photonic Glass Research Articles

2D Information Security System Based on Polyurethane Inverse Photonic Glass Structure.

Information security has become a major global problem in recent years. Thus, people continue to exert much effort in developing new information security technologies based on encryption and storage. In this study, a 2D information security technology based on polyurethane optical devices with inverse photonic glass structure (PU-IPG) is introduced. Based on 1) the swelling and plasticizing effects of various solvents on PU-IPG and 2) the capillary force that can produce geometric deformation on micro/nanostructures when solvents evaporate, a 2D information security system with two modules of decryption (structural color information display) and anticounterfeiting (structural color transformation) is successfully constructed. The spraying method adopted can be simple and fast and can provide a large area to build photonic glass templates, which greatly improves the capacity and category of information in the encryption system. The prepared PU-IPG optical devices can produce large-area multicolor output capability of information. These devices also have excellent mechanical properties, strong cycle stability, environmental friendliness, and low price. Therefore, the preparation strategy has great reference value and application prospects in the field of information security.

Mullite photonic glasses with exceptional thermal stability for novel reflective thermal barrier coatings

Thermal barrier coatings are essential materials systems for insulating and protecting substrates exposed to high temperatures. In such systems, the heat transfer has three possible paths: conduction, convection and irradiation. The higher the operating temperature, the more important it is to control or protect against the radiative component, since the radiative heat flux becomes non-negligible. The radiation can be controlled by the use of ceramic-based photonic nanostructures, namely photonic crystals and photonic glasses, creating so-called reflective thermal barrier coatings. In this work, mullite inverse photonic glasses (PhG) have been produced by thermally induced reaction on sol–gel-based silica structures coated with nanometric films of Al2O3 by atomic layer deposition. The conversion to mullite was carried out following a two-stage heat-treatment. The pre-annealing associated with the further mullite formation results in an excellent structural stability of these PhGs up to 1500 °C, being able to retain their high reflectivity in the near infrared range. Therefore, this structure can be considered for next-generation reflective thermal barrier coatings.Graphical abstract

NIR enhancement induced by refractive index differences between noble metal particles and nanocrystals in glass-ceramics

The use of optically active ions doped into photonic media containing noble metals is an intriguing area of photoluminescence (PL) research. In this paper, we present a new approach using nickel ions doped into photonic glass ceramics (GCs) containing Au metal NCs. We exploit the unique PL properties of Ni2+ embedded in ZnAl2O4 nanocrystals (NCs). Under the same conditions, the Au-ZAO duplex samples exhibit 2–3 times higher near-infrared (NIR) emission intensity and higher absorption intensity compared to the samples without Au metal. We provide direct evidence of energy harvesting around NCs through numerical simulations. The significant NIR PL properties of Ni2+ in Au-ZAO GCs can be explained by the significant dielectric coefficient difference between the Au metal, the surrounding medium, and the ZAO NCs. Furthermore, the intense and broad emission spectra of our samples cover the entire second biological NIR region, which makes them particularly useful for biomedical applications.

C-Dot-Embedded SiO2 Concentric Microspheres for Bright Fluorescent Photonic Pigments.

A simple yet powerful approach to obtain structural color is the amorphous assembly of colloidal spheres, which is also referred to as the amorphous photonic structure or photonic glasses (PGs). Additionally, the functionalization of the colloidal spheres as building blocks can further endow the resulting PGs with multifunctions. Herein, we have developed a facile strategy to prepare SiO2 colloidal spheres with concentrically embedded carbon dots (CDs). Notably, the CDs are prepared and silane-functionalized simultaneously, which enables the perfect incorporation of CDs into the Si-O network during the Stöber reaction and thus leads to the formation of a concentric SiO2/CD interlayer within the obtained SiO2 spheres. Moreover, the obtained SiO2/CD spheres can be applied as photonic pigments by assembling them into PGs, which exhibit structural color under daylight and fluorescence under UV illumination. With incorporation of carbon black, the structural color saturation and fluorescence intensity can be further manipulated. Owing to the combination of structural colored PGs and fluorescent CDs, our study can offer inspiration for color- and fluorescence-related applications such as sensing, in vivo imaging, LEDs, and anticounterfeiting.

Investigation of Ga2O3-BaO-GeO2 glasses for ultrafast laser inscription

From the perspective of developing robust mid-infrared (mid-IR) integrated photonic devices, barium-gallium-germanium (BGG) oxide glasses are strong candidates among other mid-IR glasses. Indeed, compared to fluoride, tellurite or chalcogenide glasses, BGG glasses present the highest thermal and chemical stabilities, while transmitting light up to 6 µm. In parallel to this, technological advances in ultrafast direct laser writing (UDLW)-based devices are driving the development of novel photonic glasses. Specifically, there is a need to identify the most efficient mid-infrared transmitting BGG glass compositions for sustaining the UDLW process. In this article, we thoroughly investigate the BGG physicochemical properties through absorption and Raman spectroscopies, refractive index, density, and glass transition temperature measurements in two relevant glass series: one via a Ga3+/Ge4+ ratio fixed to 1 and a barium content varying from 25 to 40 cationic percent, the other via a 2Ba2+/Ga3+ ratio fixed to 1 and a germanium content varying from 20 to 80 cationic percent. In the meantime, we explore the photosensitivity of these glasses under UDLW. Our findings reveal the valuable role of both barium and gallium ions, notably through their concentration, structural stabilization sites and viscosity influence. Finally, we demonstrate the fabrication of an 8.2 cm-long UDLW-induced waveguide with propagation losses of < 0.3 dB.cm-1 at 1550 nm.

Ga-hybridization-mediated broadband optical amplification in Bi-activated photonic glass and fiber.

A Ga hybridization strategy is proposed for simultaneously enhancing the near-infrared activity and extending the bandwidth of Bi-activated photonic glass. Systematic studies on the near-infrared optical responses of Ga/Bi and Al/Bi co-doped silica glasses are performed. It is interesting to note that Ga/Bi co-doped glasses have a similar near-infrared emission center to Al/Bi co-doped glass, while the former is more effective in improving near-infrared activity. The different luminescence mechanisms of Ga/Bi and Al/Bi co-doped silica glasses are elucidated, and the corresponding microstructure-optical response relationship is discussed. In addition, the Ga/Bi co-doped silica optical fiber is successfully prepared, and the principal fiber amplifier device is fabricated. Furthermore, amplified spontaneous emission and broadband on-off gain are realized. The results suggest that Ga-hybridized Bi-activated photonic glass is a promising gain material for broadband fiber amplifiers.

Sol–Gel Photonic Glasses: From Material to Application

In this review, we present a short overview of the development of sol-gel glasses for application in the field of photonics, with a focus on some of the most interesting results obtained by our group and collaborators in that area. Our main attention is devoted to silicate glasses of different compositions, which are characterized by specific optical and spectroscopic properties for various applications, ranging from luminescent systems to light-confining structures and memristors. In particular, the roles of rare-earth doping, matrix composition, the densification process and the fabrication protocol on the structural, optical and spectroscopic properties of the developed photonic systems are discussed through appropriate examples. Some achievements in the fabrication of oxide sol-gel optical waveguides and of micro- and nanostructures for the confinement of light are also briefly discussed.

A tunable reflector enabling crustaceans to see but not be seen

Many oceanic prey animals use transparent bodies to avoid detection. However, conspicuous eye pigments, required for vision, compromise the organisms' ability to remain unseen. We report the discovery of a reflector overlying the eye pigments in larval decapod crustaceans and show how it is tuned to render the organisms inconspicuous against the background. The ultracompact reflector is constructed from a photonic glass of crystalline isoxanthopterin nanospheres. The nanospheres' size and ordering are modulated to tune the reflectance from deep blue to yellow, enabling concealment in different habitats. The reflector may also function to enhance the acuity or sensitivity of the minute eyes by acting as an optical screen between photoreceptors. This multifunctional reflector offers inspiration for constructing tunable artificial photonic materials from biocompatible organic molecules.

A Continuous Gradient Colloidal Glass (Adv. Mater. 7/2023)

Photonic Colloidal Glass Continuous gradients in self-assembled materials can provide functionality exceeding that of the homogenous case. In article number 2208745, Markus Retsch and co-workers present a synthesis method that provides gradient size distributions via a controlled extraction emulsion process (CrEEP). The high degree of control allows the fabrication of a continuous-gradient photonic glass with enhanced broadband reflectance.

Tuning the Color of Photonic Glass Pigments by Thermal Annealing.

Thermal or solvent annealing is commonly employed to enhance phase separation and remove defects in block copolymer (BCP) films, leading to well-resolved nanostructures. Annealing is of particular importance for photonic BCP materials, where large, well-ordered lamellar domains are required to generate strong reflections at visible wavelengths. However, such strategies have not been considered for porous BCP systems, such as inverse photonic glasses, where the structure (and thus the optical response) is no longer defined solely by the chemical compatibility of the blocks, but by the size and arrangement of voids within the BCP matrix. In this study, a demonstration of how the concept of "thermal annealing" can be applied to bottlebrush block copolymer (BBCP) microparticles with a photonic glass architecture is presented, enabling their coloration to be tuned from blue to red. By comparing biocompatible BBCPs with similar composition, but different thermal behavior, it is shown that this process is driven by both a temperature-induced softening of the BBCP matrix (i.e., polymer mobility) and the absence of microphase separation (enabling diffusion-induced swelling of the pores). Last, this concept is applied toward the production of a thermochromic patterned hydrogel, exemplifying the potential of such responsive biocompatible photonic-glass pigments toward smart labeling or anticounterfeiting applications.

Structural color from pigment-loaded nanostructures.

Color can originate from wavelength-dependence in the absorption of pigments or the scattering of nanostructures. While synthetic colors are dominated by the former, vivid structural colors found in nature have inspired much research on the latter. However, many of the most vibrant colors in nature involve the interactions of structure and pigment. Here, we demonstrate that pigment can be exploited to efficiently create bright structural color at wavelengths outside its absorption band. We created pigment-enhanced Bragg reflectors by sequentially spin-coating layers of poly-vinyl alcohol (PVA) and polystyrene (PS) loaded with β-carotene (BC). With only 10 double layers, we achieved a peak reflectance over 0.8 at 550 nm and normal incidence. A pigment-free multilayer made of the same materials would require 25 double layers to achieve the same reflectance. Further, pigment loading suppressed the Bragg reflector's characteristic iridescence. Using numerical simulations, we further show that similar pigment loadings could significantly expand the gamut of non-iridescent colors addressable by photonic glasses.

A Continuous Gradient Colloidal Glass.

Colloidal crystals and glasses manipulate light propagation depending on their chemical composition, particle morphology, and mesoscopic structure. This light-matter interaction has been intensely investigated, but a knowledge gap remains for mesostructures comprising a continuous property gradient of the constituting particles. Here, a general synthetic approach to bottom-up fabrication of continuous size gradient colloidal ensembles is introduced. First, the technique synthesizes a dispersion with a specifically designed gradual particle size distribution. Second, self-assembly of this dispersion yields a photonic colloidal glass with a continuous size gradient from top to bottom. Local and bulk characterization methods are used to highlight the significant potential of this mesostructure, resulting in vivid structural colors along, and in superior light scattering across the gradient. The process describes a general pathway to mesoscopic gradients. It can expectedly be transferred to a variety of other particle-based systems where continuous gradients will provide novel physical insights andfunctionalities.

Random lasers based on inverse photonic glass structure

Random laser has attracted much attention because of its unique physical properties and potential applications in lighting, speckle-free imaging, biosensing, and photonic devices. In this work, we confirm that scattering plays a vital role in random lasing. Then, we investigate lasing properties of random film lasers with two scattering structures, including polystyrenemicroparticles and air voids embedded in a polymer matrix with organic dye serving as a gain medium. These two structures are called direct and inverse photonic glass, respectively. The result indicates that random lasers based on inverse photonic glass have a lower threshold. Following this achievement, we implemented inverse photonic glass into microspheres to obtainrandom microlasers of different sizes. Our work shows that inverse photonic glass structure is an excellent medium for random lasers with a wide range of sizes and dimensions. Especially, the obtained random microlasers are promising for applications in microsensors and photonic integrated circuits.

Using Photonic Glasses as Colored Covers for Solar Energy Harvesting

AbstractThe increasing demand for renewable energy is promoting technologies that integrate solar energy harvesting materials with the human living environment, such as building‐integrated photovoltaics. This places requirements on developing colored covers with a trade‐off between efficiency and aesthetics, providing a new stage for the large‐scale application of structural color technologies. This study investigates the theoretic feasibility of employing the photonic glass, a random packing of monodisperse dielectric microspheres, as the colored cover for solar energy harvesting. Based on numerous optical simulations, the color and average solar transmissivity of the photonic glasses with varying parameters are evaluated. Results show that using non‐absorbing microspheres with relatively high refractive index, about 3 µm thick photonic glasses can enable colors with lightness over 50 while keeping average solar transmissivity over 80%. Due to the short‐range structural correlation, it is demonstrated that photonic glasses can generate purple, blue, cyan, light green, and gray colors, but cannot help with yellow and red hues. Finally, the effects of several enhancement methods are clarified, and possible ways for expanding the color range are demonstrated. These results provide a comprehensive guide to the practical implementations of structural color using photonic glasses, particularly in the colorization of solar energy materials.

Innenrücktitelbild: Highly Efficient and Direct Ultralong All‐Phosphorescence from Metal–Organic Framework Photonic Glasses (Angew. Chem. 39/2022)

Innenrücktitelbild: Highly Efficient and Direct Ultralong All‐Phosphorescence from Metal–Organic Framework Photonic Glasses (Angew. Chem. 39/2022)

Inside Back Cover: Highly Efficient and Direct Ultralong All‐Phosphorescence from Metal–Organic Framework Photonic Glasses (Angew. Chem. Int. Ed. 39/2022)

Inside Back Cover: Highly Efficient and Direct Ultralong All‐Phosphorescence from Metal–Organic Framework Photonic Glasses (Angew. Chem. Int. Ed. 39/2022)

Three-dimensional printing of photonic colloidal glasses into objects with isotropic structural color

Structural color is frequently exploited by living organisms for biological functions and has also been translated into synthetic materials as a more durable and less hazardous alternative to conventional pigments. Additive manufacturing approaches were recently exploited for the fabrication of exquisite photonic objects, but the angle-dependence observed limits a broader application of structural color in synthetic systems. Here, we propose a manufacturing platform for the 3D printing of complex-shaped objects that display isotropic structural color generated from photonic colloidal glasses. Structurally colored objects are printed from aqueous colloidal inks containing monodisperse silica particles, carbon black, and a gel-forming copolymer. Rheology and Small-Angle-X-Ray-Scattering measurements are performed to identify the processing conditions leading to printed objects with tunable structural colors. Multimaterial printing is eventually used to create complex-shaped objects with multiple structural colors using silica and carbon as abundant and sustainable building blocks.

Highly Efficient and Direct Ultralong All‐Phosphorescence from Metal–Organic Framework Photonic Glasses

AbstractRealizing efficient and ultralong room‐temperature phosphorescence (RTP) is highly desirable but remains a challenge due to the inherent competition between excited state lifetime and photoluminescence quantum yield (PLQY). Herein, we report the bottom‐up self‐assembly of transparent metal–organic framework (MOF) bulk glasses exhibiting direct ultralong all‐phosphorescence (lifetime: 630.15 ms) with a PLQY of up to 75 % at ambient conditions. These macroscopic MOF glasses have high Young's modulus and hardness, which provide a rigid environment to reduce non‐radiative transitions and boost triplet excitons. Spectral technologies and theoretical calculations demonstrate the photoluminescence of MOF glasses is directly derived from the different triplet excited states, indicating the great capability for color‐tunable afterglow emission. We further developed information storage and light‐emitting devices based on the efficient and pure RTP of the fabricated MOF photonic glasses.

Highly Efficient and Direct Ultralong All-Phosphorescence from Metal-Organic Framework Photonic Glasses.

Realizing efficient and ultralong room-temperature phosphorescence (RTP) is highly desirable but remains a challenge due to the inherent competition between excited state lifetime and photoluminescence quantum yield (PLQY). Herein, we report the bottom-up self-assembly of transparent metal-organic framework (MOF) bulk glasses exhibiting direct ultralong all-phosphorescence (lifetime: 630.15 ms) with a PLQY of up to 75 % at ambient conditions. These macroscopic MOF glasses have high Young's modulus and hardness, which provide a rigid environment to reduce non-radiative transitions and boost triplet excitons. Spectral technologies and theoretical calculations demonstrate the photoluminescence of MOF glasses is directly derived from the different triplet excited states, indicating the great capability for color-tunable afterglow emission. We further developed information storage and light-emitting devices based on the efficient and pure RTP of the fabricated MOF photonic glasses.

Flexible random laser from a porous polymer film

Flexible random lasers have attracted a great deal of interest due to their potential in light-weight, flexible optical sensors and devices. Among many alternatives, flexible thin film random lasers are very interesting because they can be easily fabricated via a simple solution-based process. Herein, we demonstrate a dye-doped porous polyvinyl alcohol film that can work as a flexible random laser source under optical pumping. The film is fabricated by a drop cast technique and has a nearly circular shape with a diameter of ∼5 mm. Owing to the inverted photonic glass structure that is air voids in the polymer matrix, light emission from dye molecules is multiple scattering and lasing emission is achieved. In the central area, the film laser works reliably with the lasing threshold of ∼166μJ/mm2 and lasing wavelength of around 595 nm. In the edge area, the lasing properties are more fluctuated indicating that the structure may not be uniform. It is found that the lasing wavelength in the edge area is 4.5 nm red-shifted compared to that in the central area of the film. Interestingly, the thin film laser can operate well under bending conditions with a minor change in the lasing wavelength.