Morphology dependent resonance modes in highly porous TiO2 microspheres
03 Oct 2018-Journal of Applied Physics (AIP Publishing LLCAIP Publishing)-Vol. 124, Iss: 13, pp 133102-133102
TL;DR: In this paper, the authors explored the possibility of enhancing photocatalytic activity through mesoporous TiO2 spheres by exploiting the coexistence of high porosity and morphology dependent resonance (MDR) modes.
Abstract: Micro and nano structures of titanium dioxide (TiO2) are well-known for their photocatalytic application. High surface area and high light scattering efficiency in such structures enhance their photocatalytic activity. The present work explores the possibility of enhancing photocatalytic activity through mesoporous TiO2 spheres by exploiting the coexistence of high porosity and morphology dependent resonance (MDR) modes. A controlled synthesis of TiO2 spheres with nano-crystalline grains of anatase phase and high surface area of about 96 m2/g has been successfully accomplished leading to mesoporous particles with uniformly distributed pores of small diameters much less than the wavelength of incident light. Despite the high porosity, MDR modes are observed in the photoluminescence spectrum of a single sphere. As inclusion of pores may produce significant changes in the refractive index (RI) of the resonator, and as the quality and density of the modes depend on the RI of the resonator, it is important to have a procedure to determine the RI of the resonator as well as to characterize the MDR modes. An iterative procedure that is quite general is presented for mode identification and for the determination of the porosity-induced reduction in the RI and for ascertaining the presence of chromatic dispersion. The presence of high surface area as well as of MDR modes of reasonably high Q-factor makes these particles promising for photo electrochemical applications.Micro and nano structures of titanium dioxide (TiO2) are well-known for their photocatalytic application. High surface area and high light scattering efficiency in such structures enhance their photocatalytic activity. The present work explores the possibility of enhancing photocatalytic activity through mesoporous TiO2 spheres by exploiting the coexistence of high porosity and morphology dependent resonance (MDR) modes. A controlled synthesis of TiO2 spheres with nano-crystalline grains of anatase phase and high surface area of about 96 m2/g has been successfully accomplished leading to mesoporous particles with uniformly distributed pores of small diameters much less than the wavelength of incident light. Despite the high porosity, MDR modes are observed in the photoluminescence spectrum of a single sphere. As inclusion of pores may produce significant changes in the refractive index (RI) of the resonator, and as the quality and density of the modes depend on the RI of the resonator, it is important to ...
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01 May 2019
TL;DR: In this article, the authors focus on monolithic ring resonators based on total internal reflection, with a particular emphasis on nonplanar ring oscillators and whispering-gallery mode lasers.
Abstract: Monolithic total internal reflection resonators confine light through traveling waves that can feature high quality factors and small mode volumes. Such resonators have emerged as rigid and compact platforms to explore high-efficiency laser-matter interactions and their related applications in photonics technology. In this review, we focus on monolithic ring resonators based on total internal reflection, with a particular emphasis on nonplanar ring oscillators and whispering-gallery mode lasers. We also discuss resonantly enhanced nonlinear photonic systems based on these resonators, using both non-centrosymmetric and centrosymmetric optical materials.
20 citations
TL;DR: In this article, a photoanode is sensitized with CdS-CuInS2 thin films of ∼5 nm thickness, which exhibits strong coupling with optical whispering gallery modes (WGMs).
Abstract: Composite photoanode comprising mesoporous microspheres with a smooth spherical morphology exhibiting high light scattering due to optical whispering gallery modes (WGMs) is used to fabricate whisperonic solar cell (WSC) devices. The photoanode is sensitized with CdS–CuInS2 thin films (CdS–CIS-TF) of ∼5 nm thickness. CdS–CIS-TF-sensitized photoanodes exhibit strong coupling with WGM. These WSC devices show an average (ηavg) efficiency (η) of ≈3.2% in comparison with ηavg ≈ 1.9% for the nanoparticulate-based photoanode. The observed efficiency is the highest for CdS–CIS-TF-sensitized solar cells made using I–/I3– electrolyte. This remarkable increase in ηavg (∼60%) is attributed to increased photon absorption by the sensitizer films because of the presence of WGM scattering prevailing in smooth microspheres. Thus, WSC photoanode configuration is a promising approach to enhance the efficiency of TF-sensitized solar cells.
8 citations
07 Oct 2021
TL;DR: In this article, the morphology dependent resonances for the scattering of electromagnetic waves from two concentric spheres when the outer shell has a variable refractive index were investigated for both transverse magnetic and transverse electric modes and the analytic conditions to determine the resonance locations for this system were derived in the closed form of both modes.
Abstract: In many applications constant or piecewise constant refractive index profiles are used to study the scattering of plane electromagnetic waves by a spherical object. When the structured media has variable refractive indices, this is more of a challenge. In this paper, we investigate the morphology dependent resonances for the scattering of electromagnetic waves from two concentric spheres when the outer shell has a variable refractive index. The resonance analysis is applied to the general solutions of the radial Debye potential for both transverse magnetic and transverse electric modes. Finally, the analytic conditions to determine the resonance locations for this system are derived in the closed form of both modes. Our numerical results are provided with discussion.
TL;DR: In this paper, the effect of the grains on resonance modes was investigated for the perturbative effects due to nonsphericity and surface roughness and inhomogeneity in RI arising from polycrystallinity and annealing conditions.
Abstract: Morphology dependent resonance (MDR) modes in a dielectric sphere are highly sensitive to its shape, size, and refractive index (RI). Many dielectric materials with potential applications are birefringent in nature. Synthesis techniques of resonators of such materials may lead to polycrystalline morphologies. Due to its fascinating applications, titanium dioxide (TiO2) has attracted attention as a morphology dependent resonator. However, its high RI is accompanied by high birefringence. The effect of the grains on resonance modes is the interest of this study. Polycrystalline TiO2 microspheres with different grain distributions are synthesized by annealing at 500 °C and 700 °C. MDR modes in the photoluminescence spectrum of single spheres are found to exhibit mode splitting and mode shifting with respect to MDR modes of an equivalent isotropic sphere. The MDR spectral features of the near-perfect spheres have been investigated for the perturbative effects due to (a) nonsphericity and surface roughness and (b) inhomogeneity in RI arising from polycrystallinity and annealing conditions. Mode splits are demonstrated to arise from the perturbative effects of the larger grains through explicit computations using discrete dipole approximation for a Voronoi tessellated cell structure representing a polycrystalline sphere. Mode shifts are demonstrated to arise from radial inhomogeneity of the refractive index using the Aden-Kerker theory on spheres with core-shell morphology. The effects of surface roughness are not found to be significant. The present work extends the scope of model-assisted investigations in understanding morphology dependent resonators and indicates the possibility of designing resonators with prescribed refractive index features.
References
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TL;DR: In this paper, the development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed.
Abstract: Fujishima and Honda (1972) demonstrated the potential of titanium dioxide (TiO2) semiconductor materials to split water into hydrogen and oxygen in a photo-electrochemical cell. Their work triggered the development of semiconductor photocatalysis for a wide range of environmental and energy applications. One of the most significant scientific and commercial advances to date has been the development of visible light active (VLA) TiO2 photocatalytic materials. In this review, a background on TiO2 structure, properties and electronic properties in photocatalysis is presented. The development of different strategies to modify TiO2 for the utilization of visible light, including non metal and/or metal doping, dye sensitization and coupling semiconductors are discussed. Emphasis is given to the origin of visible light absorption and the reactive oxygen species generated, deduced by physicochemical and photoelectrochemical methods. Various applications of VLA TiO2, in terms of environmental remediation and in particular water treatment, disinfection and air purification, are illustrated. Comprehensive studies on the photocatalytic degradation of contaminants of emerging concern, including endocrine disrupting compounds, pharmaceuticals, pesticides, cyanotoxins and volatile organic compounds, with VLA TiO2 are discussed and compared to conventional UV-activated TiO2 nanomaterials. Recent advances in bacterial disinfection using VLA TiO2 are also reviewed. Issues concerning test protocols for real visible light activity and photocatalytic efficiencies with different light sources have been highlighted.
3,305 citations
TL;DR: Silicate mesoporous materials have received widespread interest because of their potential applications as supports for catalysis, separation, selective adsorption, novel functional materials, and use as hosts to confine guest molecules, due to their extremely high surface areas combined with large and uniform pore sizes.
Abstract: Silicate mesoporous materials have received widespread interest because of their potential applications as supports for catalysis, separation, selective adsorption, novel functional materials, and use as hosts to confine guest molecules, due to their extremely high surface areas combined with large and uniform pore sizes. Over time a constant demand has developed for larger pores with well-defined pore structures. Silicate materials, with well-defined pore sizes of about 2.0–10.0 nm, surpass the pore-size constraint ( 700 m2 g−1) and narrow pore size distributions. Instead of using small organic molecules as templating compounds, as in the case of zeolites, long chain surfactant molecules were employed as the structure-directing agent during the synthesis of these highly ordered materials. The structure, composition, and pore size of these materials can be tailored during synthesis by variation of the reactant stoichiometry, the nature of the surfactant molecule, the auxiliary chemicals, the reaction conditions, or by post-synthesis functionalization techniques. This review focuses mainly on a concise overview of silicate mesoporous materials together with their applications. Perusal of the review will enable researchers to obtain succinct information about microporous and mesoporous materials.
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TL;DR: It is demonstrated that quality factor Q - (0.8 +/- 0.1) x 10(10) of whispering-gallery modes in fused-silica microspheres at 633 nm, close to the ultimate level determined by fundamental material attenuation as measured in optical fibers, is demonstrated.
Abstract: We demonstrate the quality factor Q - (0.8 +/- 0.1) x 10(10) of whispering-gallery modes in fused-silica microspheres at 633 nm, close to the ultimate level determined by fundamental material attenuation as measured in optical fibers. The lifetime of ultimate Q is limited by adsorption of atmospheric water. Monitoring of adsorption kinetics with submonolayer sensitivity by Q factors and frequencies of whispering-gallery modes is demonstrated. The possibility of supermaterial Q's owing to intrinsic suppression of scattering losses in micropheres is discussed.
986 citations
TL;DR: A comprehensive overview of sensor technology exploiting optical whispering gallery mode (WGM) resonances by detailing the fundamental principles and theory of WGMs in optical microcavities and the transduction mechanisms frequently employed for sensing purposes.
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TL;DR: The approach presented in this study demonstrates that simultaneous control of the physical properties, including specific surface area, mesoporosity, crystallinity, morphology, and monodispersity, of the titania materials can be achieved by a facile sol-gel synthesis and solvothermal process.
Abstract: Monodisperse mesoporous anatase titania beads with high surface areas and tunable pore size and grain diameter have been prepared through a combined sol−gel and solvothermal process in the presence of hexadecylamine (HDA) as a structure-directing agent The monodispersity of the resultant titania beads, along with the spherical shape, can be controlled by varying the amount of structure-directing agent involved in the sol−gel process The diameter of the titania beads is tunable from ∼320 to 1150 nm by altering the hydrolysis and condensation rates of the titanium alkoxide The crystallite size, specific surface area (from 89 to 120 m2/g), and pore size distribution (from 14 to 23 nm) of the resultant materials can be varied through a mild solvothermal treatment in the presence of varied amounts of ammonia On the basis of the results of small-angle XRD, high-resolution SEM/TEM, and gas sorption characterization, a mechanism for the formation of the monodisperse precursor beads has been proposed to illust
407 citations