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Dynamic Emission Tuning of X-ray Radioluminescent Crystalline Colloidal Arrays: Coupling the Optical Stop Band with Sequential F?rster Resonance Energy Transfers
摘要： X-ray radiation exhibits diminished scattering and a greater penetration depth in tissue relative to the visible spectrum and has spawned new medical imaging techniques that exploit X-ray luminescence of nanoparticles. The majority of the nanoparticles finding applications in this field incorporate metals with high atomic numbers and pose potential toxicity effects. Here, a general strategy for the preparation of a fully organic X-ray radioluminescent colloidal platform that can be tailored to emit anywhere in the visible spectrum through a judicious choice in donor/acceptor pairing and multiple sequential F?rster resonance energy transfers (FRETs) is presented. This is demonstrated with three different types of ≈100 nm particles that are doped with anthracene as the scintillating molecule to “pump” subsequent FRET dye pairs that result in emissions from ≈400 nm out past 700 nm. The particles can be self-assembled in crystalline colloidal arrays, and the radioluminescence of the particles can be dynamically tuned by coupling the observed rejection wavelength with the dyes’ emission.
关键词： anthracene,F?rster resonance energy transfer,photonic crystals,X-ray radioluminescence,colloidal crystals
更新于2025-09-23 15:21:21
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Bare Silica Opals for Real-Time Humidity Sensing
摘要： The photonic properties of 3D colloidal crystals made of St?ber 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 functionalization. The optical changes are highly sensitive to humidity variation (especially in low-humidity range) and very fast response times of 60 ms, mainly ascribed to the absence of intermediate processes, the favorable bandgap characteristics (high intensity and sharp edges) and the high air accessibility to the open opal voids. Contrary to common approaches for photonic crystal sensors—seeking visual detection via large spectral shifts but having important shortcomings,—it is demonstrated that the well-defined photonic bandgap of bare silica opals allows, even for moderate shifts, outstanding sensing performance by proper monitoring with inexpensive equipment (no spectroscopic detection is needed). As a result, the rapid and reproducible photonic response enables accurate, real-time retrieval of the ambient humidity. The economical, one-step fabrication, and the efficient performance make silica artificial opals suitable for a new type of precise, low-cost, and real-time humidity sensors.
关键词： water vapor adsorption/desorption,real-time sensing,humidity sensors,artificial silica opals,photonic colloidal crystals
更新于2025-09-23 15:21:01
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Self-assembled binary photonic crystals under the active confinement and their light trapping
摘要： The self-assembly of oppositely charged colloidal ellipsoids and spheres under the active con?nement is ?rstly proposed to achieve long-range ordered photonic crystals. Compared with the conventional passive con?nement, a characteristic of the active con?nement is that boundaries are movable. Our Brownian dynamics simulations show that dynamic steady structures, similar to quasi-2D colloidal crystals, can be obtained under the strong con?nement when the two boundaries periodically oscillate together. The in-plane structures can be regulated by changing the charge ratio of the two kinds of particles. These dynamic steady structures are determined by the minimum electrostatic energy with the aid of increased mobility of con?ned particles, which are not available in equilibrium. Numerical simulations verify that light can be perfectly con?ned in this dielectric binary photonic slab without any radiation, which corresponds to a typical optical bound state with divergent lifetime and ultrasharp spectral pro?le. Given the changeable geometry of this photonic slab, the trapped optical ?eld might be applicable to enhanced light-matter interactions. In addition, for thicker layers, layer-by-layer ordered structures occur spontaneously driven by the active con?nement, while no global order in the passive con?nement. Our results show that the boundary motion can become an important factor a?ecting self-assembled structure and function.
关键词： colloidal crystals,light trapping,active con?nement,photonic crystals,self-assembly
更新于2025-09-23 15:19:57
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Self-assembly of colloidal Poly(St-MMA-AA) core/shell photonic crystals with tunable structural colors of the full visible spectrum
摘要： This study used the copolymer emulsion method to synthesize colloidal monodisperse core/shell microspheres composed of the poly(styrene-co-methyl methacrylate-co-acrylic acid) [Poly(St-MMA-AA)]. Colloidal photonic crystal (CPhC) films have prepared by using polymer composite microspheres and successfully fabricated via natural sedimentation. The synthesized results of polymer composite microsphere exhibited uniform and good morphology. The resultant of CPhC color films demonstrated vividly structural colors due to 3D CPhC nanostructures. The structural colors over full visible spectra could be tuned by controlling the filling factor of crystals and diameter of microspheres according to the Bragg law. Additionally, the structural color of Poly(St-MMA-AA) CPhC films has measured under the standard colorimetric system. This study demonstrated a approach to fabricate tunable structural color for numerous applications.
关键词： Photonic crystals,Polymer microspheres,Structural colors,Colloidal crystals,Self-assembly
更新于2025-09-10 09:29:36
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Bionic SiO2@Fc(COCH3)2 Core-Shell Nanostructure for Enhancing the Electrochromic Properties of Ferrocene
摘要： Although the properties of electrochromic materials (ECMs) have been enhanced using fabricated porous materials, the effect of materials porosity on such an enhancement remains unclear. Here, we report a novel ECMs with an adjustable pore hierarchy based on quasi-amorphous and ordered arrays of SiO2@Fc(COCH3)2. ECMs with different pore systems were generated by modifying Fc(COCH3)2 concentration and self-assembly temperature. The composition and core-shell structure of the SiO2@Fc(COCH3)2 nanospheres were confirmed through scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT-IR) and EDX mapping. The influence of adjustable pore system on the electrochemical behavior was studied. Experimental results showed that the current density of the redox couple peaks of the quasi-amorphous porous SiO2@Fc(COCH3)2 films are considerably lower than those of the ordered porous films but are higher than those of the dense Fc(COCH3)2 films. At 550 nm, the transmittance variation of the quasi-amorphous porous SiO2@Fc(COCH3)2 film is 19 %, whereas that of the ordered porous film is 35 %. The coloration and bleaching times of the quasi-amorphous porous SiO2@Fc(COCH3)2 film are 17.1 s and 4.5 s, respectively, whereas those of the ordered porous film are only 16.5 s and 3.5 s, respectively. Furthermore, the porosities of the films are solved numerically by the finite-element method. For the ordered porous SiO2@Fc(COCH3)2 film, the porosity is 0.26, while the quasi-amorphous film became larger (0.31～ 0.41). This work is the first step in combining ferrocene derivative and colloidal crystal porous structures to develop a green, simple and efficient electrochromic process.
关键词： electrochromism,adjustable porosity,colloidal crystals,ferrocene derivatives,core-shell structure
更新于2025-09-09 09:28:46
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Colloidal Crystals of NaYF <sub/>4</sub> Upconversion Nanocrystals Studied by Small-Angle X-Ray Scattering (SAXS)
摘要： Spherical NaYF4 upconversion nanocrystals with mean radii of about 5 and 11 nm are observed to form colloidal crystals, i.e., 3D assemblies of the particles with long-range order. The colloidal crystals of the larger particles form directly in solution when dispersions of the particles in toluene are stored at room temperature for several weeks. Crystallization of the smaller particles takes place when their dispersions in hexane are slowly dried at elevated temperatures. The formation and the structure of the colloidal crystals are studied by small-angle X-ray scattering (SAXS). SAXS measurements show that the smaller as well as the larger particles assemble into a face-centered cubic lattice with unit cell dimensions of a = 18.7 nm and a = 35.5 nm, respectively. The SAXS data also show that the particles in the colloidal crystals still bear a layer of oleic acid on their surfaces. The thickness of this layer is 1.5–1.8 nm, as determined by comparing the unit cell dimensions of the colloidal crystals with the mean particle sizes. The latter could be very precisely determined from the distinct oscillations observed in the SAXS data of dilute colloidal dispersions of the nanocrystals.
关键词： upconversion,colloidal crystals,nanocrystals,small-angle X-ray scattering
更新于2025-09-09 09:28:46