Position Of Photonic Band Gap Research Articles

Thermo-responsive circularly polarized luminescence from carbon quantum dots in a cellulose-based chiral nematic template

Abstract Circularly polarized light emitting active materials are of great interest, and the convenient tuning of the circularly polarized luminescence (CPL) remains a significant challenge. Integrating fluorescent materials into chiral photonic crystals to achieve tunable CPL is a promising approach, allowing efficient manipulation of CPL by adjusting the photonic band gap (PBG). We combined carbon quantum dots (CQDs) with hydroxypropyl cellulose (HPC), which self-assembles into a cholesteric liquid crystal (CLC). The helical structure can selectively reflect right circularly polarized (RCP) light, achieving strong circular dichroism (CD) and high CPL dissymmetry factor g lum. In addition, the chiral template is thermo-responsive. The CPL wavelength can be adjusted by regulating the PBG position through temperature adjustment, while the chirality of CPL keeps high especially in the heating process. This work enables stimuli-responsive manipulation of CPL under one template through temperature regulation, which may open up enormous possibilities for the cellulose-based material in different areas.

Slow Photonic Effect Inducing Improved H2 Generation in Photonic Films with Chiral Nematic Structure

AbstractIntegrating photonic crystals (PCs) into the design of a photocatalyst can significantly enhance its light‐harvesting capability. PCs can manipulate the propagation of light uniquely within a material and reduce its group velocity, thereby enhancing the absorption factor for photocatalysts. However, the slow photon effect in photoactive films with chiral nematic structures has not been reported yet, especially at the blue edge of the photonic bandgap. This work proposes a straightforward one‐pot method to fabricate various photonic films with chiral nematic, namely g‐C3N4/SiO2, TiO2/SiO2, and g‐C3N4/TiO2/SiO2. The sol‐gel biotemplating formulation using cellulose nanocrystals successfully leads to the elaboration of films exhibiting variable iridescent colors with photonic bandgap from UV to visible range. The tunable wavelength of the Bragg peak reflection offers the opportunity to access a region with a slow photonic effect, which directly impacts the light‐harvesting properties of the photoactive material. It is demonstrated that the H2 generation is significantly enhanced when the blue edge of the photonic bandgap position overlapped with the absorbance band of the photocatalyst. These results offer the opportunity to design photonic materials with chiral nematic structure and optimize the photocatalytic performance for energy application.

Effect of the Photonic Band Gap Position on the Photocatalytic Activity of Anodic Titanium Oxide Photonic Crystals

Effect of the Photonic Band Gap Position on the Photocatalytic Activity of Anodic Titanium Oxide Photonic Crystals

Effect of the photonic band gap position on the photocatalytic activity of anodic titanium oxide photonic crystal

The slowing down of the group velocity of light at the edges of the photonic band gap is one of the important optical effects observed in photonic crystals. In particular, the “slow light” effect is used in photocatalysis to increase the photocatalytic activity of semiconductors. In this work, anatase photonic crystals with different spectral positions of the photonic band gap (390–1283 nm, measured in water) were obtained. It is shown that if one of the photonic band gaps is located near the absorption edge of the semiconductor (410 nm), photonic crystal exhibits high photocatalytic activity in the photodegradation of methylene blue. At the same time, the photocatalytic activity of anatase photonic crystal increases by 30% when the photonic band gap of the third order rather than the first order is located near the absorption edge of the semiconductor.

A new approach to the synthesis of anodic titania photonic crystals with desired position and high reflectance of photonic band gaps

Anodic titanium oxide photonic crystals (ATO PhCs) are promising for optical sensing and photocatalysis due to their photonic band gaps (PBGs). The ability to control the spectral position and width of the PBG are essential for application of ATO PhCs. Anodizing charge density has recently been reported to be a main factor affecting the porosity and hence the effective refractive index (neff) and PBG position of ATO PhCs. In this paper, we propose a method for accurate determining the dependence of neff of ATO PhCs on the etching charge density varying in a wide range. The method is based on an analysis of the spectral positions of PBGs in photonic heterostructures. The obtained dependence was used for the synthesis of the ATO PhCs with desired PBG positions in a wide wavelength range (400–1500 nm) by the periodic voltage modulation on optical path length. The deviation of the experimental PBG position from the specified one does not exceed 10 %. The prepared PhCs possess ∼100 % reflectance in the PBG region.

Anodizing charge density controls the porosity of anodic titanium oxide photonic crystals

Anodic titanium oxide (ATO) one-dimensional photonic crystals (PhCs) are materials with uniaxial periodic modulation of porosity. A periodic change of an effective refractive index caused by porosity modulation results in the formation of photonic band gaps (PBGs). The non-uniform dissolution of ATO cell walls during the fabrication process hampers the obtaining of a strict optical periodicity of ATO PhCs. Recently it was found that the dissolution of ATO cell walls is accelerated by anodic polarization. However, the main factor controlling the accelerated dissolution of ATO cell walls during anodizing remains unclear. In this study, the correlation between ATO PhC porosity and the charge density is discussed. The dependencies of the spectral photonic band gap (PBG) position and PBG reflectance on the charge density are studied experimentally. The findings open a pathway to the synthesis of ATO PhCs with flawless optical periodicity and high PBG reflectance.

Investigation of photonic band gap properties of one-dimensional magnetized plasma spherical photonic crystals

Utilizing the transfer matrix method (TMM), the magnetic and electric field equations of Maxwell’s system of equations in the spherical coordinate system are constructed. By combining the solution of the spherical Bessel equation to theoretically treat the magnetic and electric fields of a one-dimensional (1-D) magnetized plasma spherical photonic crystals (MPSPCs), detailed expressions for the transmission properties and dispersion relations of 1-D MPSPCs are obtained. The structure of 1-D MPSPCs is also designed, and the effects of the cyclotron frequency of plasma, incidence angle, collision frequency, plasma frequency, structure, dissipation factor and plasma thickness on the photonic band gaps (PBGs) features are discussed. With the adjustment of these parameters, the impact of the collision frequency on the transmission properties is extraordinarily insignificant. The plasma frequency and the cyclotron frequency of plasma have quite similar effects on the PBGs. The variation of incidence angle and plasma frequency thickness affects not only the position of PBGs but also the amount of them. The difference in structure and the change in dissipation factor have no effect on the distribution of PBGs and only a slight effect on the amplitude of the transmission spectra.

Collective modulation of upconversion in Ag-BaTiO3: Yb3+, Er3+ by photonic bandgap and surface plasmon resonance effects

A series of Ag-BaTiO3: Yb3+, Er3+ inverse opal structures were synthesized by co-precursor sol-gel method. Under near-infrared excitation, the enhanced upconversion emissions were obtained by the coupling of photonic band gap and surface plasm on resonance effects. The green and red luminescence of Ag-BaTiO3: Yb3+, Er3+ were up to 14.2-fold and 12.8-fold higher than the reference sample, respectively. In addition, a rate equation model has been established based on the energy transfer processes, and a thorough analysis has been conducted to clarify the influence of two effects. By altering the photonic bandgap position, corresponding spontaneous emissions could be inhibited and the efficiency of incident light could be improved. With the introduction of plasmonic structures, the green to red ratio was able to be manipulated by the Purcell factor of radiative decay rate and the additional nonradiative decay channels described by Wnr. This work employs an intriguing strategy for modulating and enhancing upconversion luminescence, which is of great value for potential applications in displays and bio-lables.

Microfluidic-Blow-Spinning fabricated sandwiched structural fabrics for All-Season personal thermal management

The concept of personal thermal management (PTM) has successfully been proven in heating and cooling fabrics, which can not only improve human comfort, but also reduce energy consumption. However, it remains a huge challenge to integrate the two opposite functions of heating and cooling in the same fabric by adaptive thermal management. Herein, a sandwiched structural fabric featuring both passive reflection cooling derived from photonic crystals (PCs) layer and active heating rooted in nano-Ag layer are generated by adjusting photonic band gap position and applied voltage changes. The passive reflection cooling of sandwiched structural fabric offers improved effect over the normal cotton, and the high absolute temperature difference reaches 7.9 °C. Besides, when a low voltage of 3 V is applied, the extra heating temperature difference of Joule heating realizes 18.1 °C due to the good electrical conductivity of nano-Ag. Moreover, we have successfully constructed a wearable PTM device to adjust temperature of human body by using this sandwiched structural fabric with excellent flexibility, breathability and high mechanical strength. Therefore, this strategy presents an easy-to-manipulate platform for the fabrication of sandwiched structural fabrics and provides new insights for PTM applications.

Pre-compressed polymer cholesteric liquid crystal based optical fiber VOC sensor with high stability and a wide detection range.

As the concentration of VOC gases is very high in organic chemical reactions, in order to ensure the safety and accuracy of the experiment, it is very important to develop a gas sensor with a wide detection range. Exploring the mechanism and law of photonic bandgap (PBG) shift after absorption of volatile organic compounds (VOCs) vapors are two basic premises of resolving the PCLC for gas detection with a wide measurement range and stability. Herein, the PCLC films doped with different concentrations of polymer are used for acetone vapor detection, and the shift law of the PBG position is analyzed. As the increase of the detected gas concentration, the intractable problem is that the PBG position of PCLC exhibits red- and blue-shifts successively. Particularly, the pre-compressed technique is highly important for development of a high-performance PCLC based fiber probe, which is crucial for effectively solving the bottleneck problem mentioned. It enables detection of a wide range of acetone vapor concentration from 0 ppm to 50×104 ppm, and the corresponding mean sensitivity of 0.23 pm/ppm. In addition, the thermal crosstalk is generally negligible at temperature below 40°C. Therefore, it is a breakthrough that the described technique not only effectively enhances the stability and robustness of the PCLC fiber probe for VOC vapor detection, but also improves its sensitivity and detection range. The pre-compressed technique provides a novel avenue for fabrication of other PCLC-based devices.

Tuneable fluorescence and structural colour in PNIPAM microgel assemblies

The combination of fluorescence and structural colour in colloidal photonic glasses could be the starting point for the design of dynamic multiple responsive colloidal photonic materials for advanced applications in which the fluorescence intensity could be modulated by stimulus-induced colour changes. The merocyanine functionalization of the PNIPAM-based microgel system made it possible to obtain tuneable photonic colloidal glasses displaying vivid structural colours and fluorescence. For this purpose, the MC was introduced in some of the crosslinking points of the inner structure of a PNIPAM-based microgel system. These building blocks were left to organize in water (pH 4.5) to obtain photonic glasses. The structural colour was studied as a function of water concentration, so that increasing the microgel concentration led to a blue colour shift. The PBG was characterized by diffuse reflectance spectroscopy. Reflection imaging microscopy was used to understand the microstructure responsible for the PBG. It could be determined that the microgel particles decreased their diameter from 430 nm up to 220 nm to adjust to the glass organization. It has been found that MC fluorescence intensity in these assemblies depended on the photonic band gap (PBG) position in such manner, that strong quenching of MC fluorescence was observed when the PBG matched the MC excitation wavelength. Besides, the MC fluorescence excitation band was 10 nm shifted to higher wavelengths.

Polarization-enhanced cell walls etching of anodic titanium oxide

Anodic titanium oxide (ATO) photonic crystals (PhCs) are promising for photonics, photocatalysis, and solar cells. A refractive index modulation in ATO PhCs is caused by the modulation of porosity and, thus, the pore diameter should be controlled precisely. The ATO cell walls etching in electrolyte solution during anodizing increases the porosity of the PhC structure and shifts the photonic band gap (PBG) position to shorter wavelengths. Until now, the ATO cell walls etching in organic based electrolytes has been associated solely with the chemical dissolution of ATO in fluoride-containing solutions. Here, a significant enhancement of cell walls etching is observed when electric current flows under anodic polarization. This effect leads to the blue shift of the PBG position with the number of periods of ATO PhC structure. Therefore, it is essential for the synthesis of ATO PhCs with a precise PBG position.

Optical properties of colloidal crystals with structural colors on paper substrates using a rapid coating technology

Structural colors generated by colloidal crystals offer a promising method to create large-scale nanostructures due to their stability in comparison with dyes and pigments. However, the low durability and the low efficiency of colloidal crystals limit their practical applications. In this work, a rapid coating technology was applied in fabricating colloidal crystals on paper substrates with silicon dioxide microspheres in order to develop a fast and efficient method to produce structural colors. It was confirmed that the silicon dioxide colloidal microspheres could form a uniform photonic crystal film on papers in the end of the assembly process, and the formation mechanism of photonic crystal on papers were proposed. The optical properties of structural colors on papers were investigated and the position of photonic band gap was characterized. The results showed that the varied structural colors across the visible region confirmed by reflectance spectra could be adjusted by controlling the sizes of the microspheres and viewing angles, and this was consistent with the law of the Bragg diffraction. The CIE1976L*a*b* values of the structural colors were in agreement with their reflectance spectra. The rapid coating technology producing colloidal crystals is efficient with low cost and high adhesion, which can be used in the design and application of green printing and packaging industries.

A new route to designing a one-dimensional multiperiodic photonic crystal with adjustable photonic band gap and enhanced electric field localization

In this paper, photonic band gap (PBG) properties and electric field distribution of a one-dimensional multiperiodic photonic crystal were theoretically calculated based on a 2 × 2 transfer matrix method (TMM) using MATLAB software. Stacked layers of Nb2O5, Si and TiO2 were designed as a new model of the one-dimensional three-periodic photonic crystal. The results show that by changing parameters such as the layers order, number of periods, thickness of layers, defect layer thickness and the angle of incident, it is possible to engineer the width and position of PBG while also increasing the electric field intensity inside the photonic crystal. It is shown, that the [NS]2 [T]1 [NS]8 structure (N = Nb2O5, S = Si and T = TiO2) has a wider photonic band gap (PBG) allowing for applications such as laser eye protections. The [NS]2 [T]2 [NS]8 structure is found to be the highest in terms of localization of light in defect layer and being suitable for use in the photocatalysis field.

Investigation of reflectance properties in a symmetric defective annular semiconductor–superconductor photonic crystal with a radial defect layer

The transfer matrix method is used to investigate the reflectance properties in a symmetric defective annular photonic crystal (APC) containing semiconductor, high-Tc superconductor and a radial defect layer. Numerical results offer many noteworthy features that can be very useful in designing optical devices. In this regard, the geometric effects of alternate layers on the optical reflectance of our defective APC structure by changing the thickness of different layers would be investigated. Then, the possibility of controlling the spectral position of existed photonic band gaps (PBGs) and defect modes would be discussed by our analysis. In addition, it is found that the characteristics of the reflectance spectrum and subsequently, the spectral position of PBG and defect mode are entirely independent on changes in the starting radius of the hollow core. This characteristic is desirable to manufacturers, since increasing the size of the core radius would offer flexibility and simplicity of fabrication in producing optical devices. This study reveals that the optical reflectance of defective APCs is strongly dependent on the azimuthal mode number. Lastly, our results show that by increasing the temperature of the superconductor layer, both of the existed band gaps and defect mode show a red-shift trend by moving toward higher wavelengths. The proposed structure and related results can lead to gain valuable information for designing and fabrication of new types of annular Bragg resonators surrounding a radial defect and integrated visible waveguide devices like optical switches and filters.

The influence of shape and orientation of scatters on the photonic band gap in two-dimensional Bravais-Moiré lattices

We perform a theoretical study of light propagation properties in two-dimensional square photonic crystals following Bravais-Moiré patterns, paying particular attention to the influence of the transversal shape and the orientation of the dielectric scatters onto the width and position of photonic band gaps. In this sense, we have considered both square and triangular transversal geometries for the dielectric scatters, together with the possible rotation of either all the elements or of one half of them, within the unit cell. Results for the photonic dispersion relations and band gaps are compared with those arising from the analysis of structures with simple bi-atomic Bravais unit cells. It comes out that wider photonic gaps appear when using square-shaped scatters. The use of Bravais-Moiré cells with the same kind of cores enhance the width of these gaps but shift them towards higher frequencies. Rotation of all elements within the cell in angles of 0.23 rad and 0.46 rad causes very small, if not null, changes in the photonic gap widths. However, the rotation of one half of the scatters in the cell, leaving the other half unrotated does produce noticeable modifications in the photonic band structure: For crystals made of square-shaped dielectric cores and simple cubic cells, this rotation strongly modifies the photonic structure, whilst for Bravais-Moiré crystals the same kind of change takes place for cells made of triangular-shaped cores.

Titania Photonic Crystals with Precise Photonic Band Gap Position via Anodizing with Voltage versus Optical Path Length Modulation.

Photonic crystals based on titanium oxide are promising for optoelectronic applications, for example as components of solar cells and photodetectors. These materials attract great research attention because of the high refractive index of TiO2. One of the promising routes to prepare photonic crystals based on titanium oxide is titanium anodizing at periodically changing voltage or current. However, precise control of the photonic band gap position in anodic titania films is a challenge. To solve this problem, systematic data on the effective refractive index of the porous anodic titanium oxide are required. In this research, we determine quantitatively the dependence of the effective refractive index of porous anodic titanium oxide on the anodizing regime and develop a model which allows one to predict and, therefore, control photonic band gap position in the visible spectrum range with an accuracy better than 98.5%. The prospects of anodic titania photonic crystals implementation as refractive index sensors are demonstrated.

Upconversion luminescence modification induced near infrared luminescence enhancement of Bi2Ti2O7:Yb3+, Er3+ inverse opals

To date, there are comprehensive researches on rare-earth doped photonic band gap (PBG) materials. The PBG materials can effectively modify the up-conversion luminescence (UCL) of rare earth ions. However, few people pay attention to the influence of modification of the UCL of rare earth ions on their near infrared (NIR) luminescence. In this article, the Bi2Ti2O7: Yb3+, Er3+ inverse opal PBG materials were prepared, and the influence of modification of the UCL of Er3+ on their NIR luminescence was investigated systematically by changing the PBG position. The green and red UCL were suppressed when the PBG was overlapped the UCL of Er3+. The UCL modification induced NIR luminescence enhancement was observed in the Bi2Ti2O7: Yb3+, Er3+ inverse opal, which was attributed to the energy redistribution caused by the PBG effect. The suppression of UCL results in that the electrons located at the UCL levels relax to the NIR luminescence level of 4I13/2, causing the NIR luminescence enhancement. Our research can provide a promising method for the enhancement of the NIR luminescence.

Anodic titanium oxide photonic crystals prepared by novel cyclic anodizing with voltage versus charge modulation

Photonic crystals based on titania are of great practical importance in modern photonics owing to a variety of possibilities for their applications in optoelectronics, sensorics, and solar photovoltaics. However, the reproducible, scalable, and low-cost method of the preparation of titania photonic crystals with desired optical characteristics is still absent. Here the novel anodizing regime with voltage versus electric charge modulation, U(Q), is suggested for the precise morphology control of anodic porous films of valve metals oxides. The potential of the suggested approach is demonstrated on the preparation of high-quality one-dimensional titania photonic crystals. A new type of anodic titania nanotubes possessing periodic change of inner diameter and constant outer diameter is prepared using sine-wave modulation of applied voltage with electric charge. The possibility to tune the position of photonic band gap within the whole visible spectrum is shown.

Improved upconversion efficiency and thermal stability of NaYF4@SiO2 photonic crystal film

Fluorescent photonic crystal films (PCFs), which consisted of monodisperse NaYF4:10Yb, 0.5Tm@SiO2 or NaYF4:10Yb, 0.5Er, 0.2Tm@SiO2 core-shell spheres (10%, 0.5% and 0.2% represent the reactant mole percentage), were successfully fabricated. The morphologies and structures of PCFs were measured, while the fluorescent properties of NaYF4 in PCFs with different photonic band gap (PBG) positions were investigated. Besides, the energy transfer process in thermal coupled energy levels of NaYF4:10Yb, 0.5Tm@SiO2 under different temperatures was discussed. The results indicated that the short wave emission of NaYF4 can be enhanced by the regulation of photon mode density (PMD) in photonic crystals. Particularly, when the infrared 800 nm emission peak was in the range of PBG position of the PCF sample, the energy transfer process of 3H4-3H6 was suppressed and the short wave emission was enhanced by 1.64 times. Due to the well thermal radiation ability of silica shell, the thermal coupled energy levels (3F3 and 3H4) of NaYF4:10Yb, 0.5Tm@SiO2 core-shell spheres exhibited more stable emission intensities than NaYF4:10Yb, 0.5Tm nanoparticles, when the experimental temperatures varied from 30 to 300 °C.