共查询到20条相似文献,搜索用时 0 毫秒
1.
L. P. Avakyants V. S. Gorelik L. I. Zlobina N. N. Mel’nik P. P. Sverbil’ A. B. Fadyushin A. V. Chervyakov 《Inorganic Materials》2006,42(6):635-640
We have studied light scattering in synthetic opal crystals infiltrated with ferroelectric sodium nitrite, NaNO2, and have analyzed simple models for the energy band structure of photonic crystals. Expressions have been derived for the group velocity of photons whose energy is close to the photonic band gap. Our results indicate that the infiltration of photonic crystals with NaNO2 markedly increases the Raman scattering intensity. 相似文献
2.
Yu. P. Voinov N. F. Gabitova V. S. Gorelik G. A. Emel’chenko V. M. Masalov 《Inorganic Materials》2009,45(8):894-899
We analyze the reflectivity spectra of synthetic opal crystals (sphere diameters of 200, 240, and 290 nm) infiltrated with ferroelectric sodium nitrite (NaNO2) after preannealing in air or argon. The reflectivity spectra of the opal samples show a band corresponding to the photonic band gap. Its position and shape strongly depend on the sphere diameter and annealing conditions. The spectra of the sodium-nitrite-infiltrated opal samples preannealed in air differ markedly from those of the samples preannealed in argon. The experimentally determined band gap position as a function of sphere diameter is compared to calculation results. Our data demonstrate that argon preannealing ensures effective infiltration of molten sodium nitrite into the pores of synthetic opal. 相似文献
3.
Reflection spectra of the (111) surface of synthetic opal crystals with sphere diameters of 210, 250, and 300 nm have been measured at room and liquid-nitrogen temperatures. At cryogenic temperatures, we observed a narrowing and shift of photonic band gaps due to liquid nitrogen infiltration into the opal pores. We have calculated ω(k) dispersion relations and determined the reflectivity of the opal surface. The results have been compared to the measured reflection spectra. We have detected photon conversion from the edges of the band gap to its center. 相似文献
4.
V. S. Gorelik Yu. P. Voinov G. A. Emel’chenko V. M. Masalov N. I. Yurasov V. V. Gryaznov 《Inorganic Materials》2009,45(6):645-650
We analyze broadband visible reflectivity spectra of opal photonic crystals annealed in an argon atmosphere and air. Scanning electron microscopic examination has shown that the crystals consist of close-packed spheres with a mean diameter in the range 200–290 nm. Incorporation of even small amounts of carbon (?0.5 wt %) increases the density of the opal matrix. The presence of carbon shifts the Bragg reflection peak of the opal and increases its intensity. 相似文献
5.
The emission spectra of opal photonic crystals loaded with silver nanoparticles have been measured in a 180° geometry under UV and visible excitation. The spectra of silver-infiltrated opal under excitation through optical fibers are found to differ from the spectra of plain (uninfiltrated) opal: the infiltrated silver shifts the emission maximum to longer wavelengths and changes the shape of the spectrum. We have calculated the dispersion laws for two photonic bands and the corresponding frequency dependences of the refractive index for the photonic crystals studied. 相似文献
6.
Reflection spectra of the (111) growth surface of opal photonic crystals differing in silica sphere diameter have been measured under illumination with narrowband ultraviolet and violet light from a laser and light-emitting diodes and with broadband light from a halogen lamp. We have found narrow strong bands differing in spectral position from the light from the short-wavelength excitation sources. The spectral position of these bands corresponds to that of photonic band gaps and is independent of excitation wavelength. The silica sphere diameter has no effect on the shape of the reflection band, and its position always correlates with that of the band gap of the opal. The present results demonstrate that exposure of a photonic crystal to short-wavelength radiation leads to conversion of the radiation to the spectral range of the band gap. The microscopic mechanism of the conversion process may involve three-photon parametric processes and amplification of the broadband photoluminescence due to structural defects in the silica matrix. Our results open up the possibility of creating new types of optically pumped solid gain media based on opal photonic crystals. 相似文献
7.
This paper presents a theoretical analysis of conditions for the propagation of electromagnetic waves in a wide frequency
range (from the infrared to ultraviolet spectral region) in synthetic opals infiltrated with water and gold nanoparticles.
A dispersion equation is derived which describes the dispersion law of both “right-hand” (right-hand system of the [(E)\vec]\vec E, [(H)\vec]\vec H, and [(k)\vec]\vec k vectors) and “left-hand” (left-hand system of the [(E)\vec]\vec E, [(H)\vec]\vec H, and [(k)\vec]\vec k vectors) electromagnetic waves in the crystals. We have determined the dispersion characteristics of the refractive index
and broadband reflectance of the opals, group velocity dispersion, and effective mass dispersion for phonons and polaritons.
Theoretical results are compared to measured reflection spectra. 相似文献
8.
V. S. Gorelik N. I. Yurasov V. V. Gryaznov Yu. P. Voinov P. P. Sverbil’ M. I. Samoilovich 《Inorganic Materials》2009,45(9):1013-1017
We have studied the optical properties of opal photonic crystals infiltrated with the M0.35Zn0.65Fe2O4 (M = Ni, Co) ferrites. The crystals consisted of amorphous SiO2 nanospheres. The visible reflectivity spectra of the crystals were used to determine parameters of their photonic band gap
and their refractive index. 相似文献
9.
Infiltration of opal with nonlinear optical materials is shown to markedly raise its emission intensity in the visible range under pulsed laser excitation. Evidence is presented for three-photon parametric scattering in both uninfiltrated and infiltrated globular photonic crystals, with excitation of “slow” photons in the visible range. Our results indicate that synthetic opal crystals can be used as photon traps for studying the emission spectra of organic and inorganic materials infiltrated in opal pores. 相似文献
10.
We have studied the reflection spectra of opal photonic crystals with air-or ethanol-filled pores at different diameters of the silica spheres. An experimental technique has been proposed which enables identification of both the first and second photonic band gaps in the reflection spectrum of opal. The ability to observe the second band gap allowed us to derive a dispersion relation for the refractive index of the infiltrated substance. The calculations were performed using a model for a one-dimensional periodic layered medium with two refractive indices. We obtained ω(k) dispersion curves for electromagnetic waves in a photonic crystal (at normal incidence). The ω(k) dispersion law was used to find a dispersion relation for the reflectance of the photonic crystal. 相似文献
11.
V. S. Gorelik L. I. Zlobina V. A. Karavanskii O. A. Troitskii R. I. Chanieva 《Inorganic Materials》2010,46(8):862-865
A technique has been developed for infiltrating gold nanoparticles into the pores of synthetic opal using laser ablation and
high-temperature annealing, and the reflection spectra of gold-infiltrated opal photonic crystals have been measured. When
a halogen lamp was used as a broadband light source, the peak-reflection wavelength of the gold-infiltrated opal was longer
than that of the uninfiltrated opal. We calculated the dispersion laws for the two lower photon bands of the synthesized photonic
crystals and obtained the corresponding frequency dependences of the refractive index. 相似文献
12.
We have measured photoluminescence (PL) and broadband reflection spectra of the surface of an opal photonic crystal (OPC) filled with terbium nitrate hexahydrate (TNH). The excitation sources used were a halogen lamp, lasers with emission wavelengths of 266 and 337 nm, and semiconductor light-emitting diodes (369 and 385 nm). It has been shown that resonance excitation of the TNH (Tb(NO3)3 · 6H2O) filled OPC by pulsed laser light at a wavelength of 266 nm gives rise to superluminescence: an increase in the relative intensity of the 545-nm PL band, corresponding to the Tb3+ 5 D 4–7 F 5 transition. The efficiency of pumping the upper laser level of the OPC increases due to the increase in the density of photon states (Purcell effect) near the bandgap edge in the OPC. The lack of clear superluminescence under excitation by the other excitation sources is related to specific features of the absorption of incident light by the rare-earth ion and to the low output power of the cw light sources. 相似文献
13.
We obtained upconversion (UC) light-emitting photonic materials (YbPO(4):Er) with an inverse opal structure by the self-assembly technique in combination with a solgel method. The effect of the photonic stopband on the UC luminescence of the (2)H(11/2), (4)S(3/2)→(4)I(15/2), and (4)F(9/2)→(4)I(15/2) transitions of Er(3+) has been observed in the inverse opals of the Er(3+)-doped YbPO(4). Significant suppression of the UC emission was detected if the photonic bandgap overlapped with the Er(3+) ions emission band, while enhancement of the UC emission occurs if the emission band appears at the edge of the bandgap. 相似文献
14.
We demonstrate that the width and spectral position of the band gap of opal photonic crystals can be controlled by varying
the concentration of solution in the opal pores. An experimental technique is proposed which enables identification of both
the first and second photonic band gaps in the reflection spectrum of opal. The ability to observe the second band gap allows
a dispersion relation to be derived for the refractive index of the infiltrated substance. The calculations are performed
using a model for a one-dimensional periodic layered medium with two refractive indices. We obtain an ω(k) dispersion relation and the reflection spectra of a photonic crystal in the [111] direction at different solution concentrations. 相似文献
15.
The phase diagrams of the ternary liquid systems [Ce(NO3)3(TBP)3]-C10H22-[UO2(NO3)2(TBP)2] and [Ce(NO3)3(TBP)3]-C10H22-[Th(NO3)4(TBP)2] and of the quaternary liquid system [Ce(NO3)3(TBP)3]-C10H22-[UO2(NO3)2(TBP)2]-[Th(NO3)4(TBP)2] at T = 298.15 K are constructed. The phase diagrams are characterized by areas of homogeneous solutions and of two-phase liquid systems (systems with phase separation), with one phase (I) enriched in [Ce(NO3)3(TBP)3], [Th(NO3)4(TBP)2], and [UO2(NO3)2(TBP)2], and the other phase (II), in C10H22. Using the data on the mutual solubility of the components in the systems under consideration and equations of the NRTL model, the parameters of intermolecular interactions and the excess Gibbs energies (G ex) were calculated for the binary, ternary, and quaternary systems. Passing from the ternary system [Ce(NO3)3(TBP)3]-C10H22-[Th(NO3)4(TBP)2] to the quaternary system [Ce(NO3)3(TBP)3]-C10H22-[UO2(NO3)2 (TBP)2]-[Th(NO3)4(TBP)2] does not appreciably affect the distribution of C10H22 between phases I and II, but leads to the redistribution of [Ce(NO3)3(TBP)3] into phase II and of [Th(NO3)4(TBP)2] into phase I. 相似文献
16.
B. A. Aminov M. A. Hein G. Müller H. Piel D. Wehler Ya. G. Ponomarev K. Rosner K. Winzer 《Journal of Superconductivity and Novel Magnetism》1994,7(2):361-365
Tunneling effects in YbBa2Cu3O7?x (YbBCO) and YbBa2Cu3O7?x (YBCO) single crystals have been investigated using an improved technique of break junction preparation. A two-gap structure with BCS-like density of states has been observed. The value of the “large” gap is in the range of 24–28 meV for YBCO (T c =85–90 K) and 29–30 meV for YbBCO (T c =87–90 K). A variation of the value of the “small” gap between 0.5 and 11 meV has been detected, even for the same crystal. As a possible explanation, two-band superconductivity, surface properties, or strong gap anisotropy will be discussed. 相似文献
17.
18.
T. Klein W. Harneit L. Baril C. Escribe-Filippini 《Journal of Low Temperature Physics》1996,105(3-4):1067-1072
Pinning and vortex dynamics have been investigated in the 3-dimensional copper free (K, Ba)BiO3superconductor (Tc 31K) by magnetization and transport measurements up to 30 Tesla. The magnetization curves present a pronounced fishtail effect which persists for time scales down to 10–4s (pulsed field measurements). We show that it is an intrinsic feature of the critical current which can in part be well described by the collective pinning theory. Furthermore, this system presents evidence for a vortex liquid /glass transition for vanishingly small currents. As the current density is increased, dissipation in the glass state is dominated by creep effects. The temperature and current dependence of the activation energy is discussed. 相似文献
19.
J. P. Grammatico J. M. Porto Lopez 《Journal of Materials Science: Materials in Electronics》1992,3(2):82-86
The reaction sequences during BaTiO3 formation from the systems Ti(OiPr)4 + Ba(CH3COO)2 and TiO2 + Ba(CH3COO)2 are studied, using a sol-gel method for the former system and solid-state reaction for the latter. The sol-gel system exhibits greater reactivity, forming BaTiO3 at temperatures as low as 500°C; also, the formation of the intermediate Ba2TiO4 occurs to a much lesser extent than in the case of solid-state reaction. An explanation of the structure and behaviour of the gel system is proposed from X-ray diffraction, infrared and thermogravimetric examinations. Under appropriate treatments, both systems yield microstructures with fine and homogeneous grain size; however, the sol-gel method facilitates a complete reaction at temperatures appreciably lower than those needed with the solid-state reaction system. 相似文献