Eu doped silica xerogel luminescent layer having antireflection and spectrum modifying properties suitable for solar cell applications

A spectrum modifying glassy luminescent layer with antireflection properties has been prepared with Eu³⁺ ions embedded in silica gel for solar cell applications. Preparation of such matrix by sol-gel process and change in luminescence properties in transforming from amorphous to crystalline phase are described. Luminescent Eu³⁺ species in amorphous silica matrix show intense red emission at 614 nm by absorbing UV/blue light. Amorphous environment with reduced symmetry for Eu³⁺ ions results in an unprecedented short decay time of 145 μs for ⁵D₀-⁷F₂ electric dipole transition. In the crystalline monoclinic phase of Eu₂O₃ nanoparticles, concentration quenching of Eu³⁺ species reduces luminescence output.     

Encapsulation of aromatic oxygen palladium phthalocyanine in silica xerogel and its optical limiting property

Metallophthalocyanines (MPc) exhibit, among many useful properties, the ability to protect sensors against short, intense pulse deleterious to efficient sensor operation. For the successful application of this optical limiting property, an important issue is the incorporation of MPc molecules in a matrix to fabricate a solid state system. We report here the study of different concentrations of aromatic oxygen palladium phthalocyanine (ArOPdPc) encapsulated in silica xerogel obtained by the sol–gel technique. The resulted composites were transparent and homogeneous with the required optical limiting properties. The trapping effect was confirmed by the characteristic absorption bands of ArOPcPd in the UV–Vis spectra. The optical limiting properties of the composites were measured at 532 nm with 8 ns pulses. The results showed that the composites had obviously optical limiting effect, owing to the existing of large amount of monomers and the introduction of palladium atom in the cavity of phthalocyanine ring.     

Effect of doping levels on the pore structure of carbon nanotube/silica xerogel composites

This letter reports the effect of CNT doping levels on the pore structure of carbon nanotube (CNT)/silica xerogel composites, which would greatly influence the composite's physical behaviors and their applications in the field of optics. The composites were prepared by sol-gel technique and carried out pore structure analysis. The results show that there are mainly two grades of pores, centering at 8 and 15 nm respectively, that existed in the structure. The relative ratio of the two-grade pores, also BET surface area and pore volume of the composites, change with the different CNT doping levels. The reason may be that the addition of CNTs can act as inhomogeneous crystalline sources, seduce the silica xerogel network to grow around them and therefore change the gel formation process of silica granules.     

Preparation and optical limiting properties of carbon nanotubes coated with Au nanoparticle composites embedded in silica gel-glass

Au nanoparticle (NP) coated carbon nanotubes (CNTs) (CNTs@AuNPs) embedded in silica gel-glass (CNTs@AuNPs/silica gel-glass) were prepared by the sol-gel technique. Subsequent analysis confirmed the successful introduction of the CNTs@AuNPs to the silica gel-glass. Coating with AuNPs dramatically improved the mechanical properties of the silica gel-glass matrix, despite the higher Brunauer-Emmett-Teller (BET) specific surface area and pore volume of the CNTs@AuNPs/silica gel-glass compared with CNT/silica gel-glass. The optical limiting (OL) properties of the CNTs@AuNPs measured at a laser wavelength of 532 nm were slightly weaker after introduction into the solid-state matrix. This reduction is probably attributed to the synergistic nonlinear optical effects of reverse saturable absorption arising from the CNTs and saturable absorption from the AuNPs embedded in the silica gel-glass.     

Optical properties of chlorophyll-doped silica gels

Optical characterization is presented for a silicon oxide amorphous matrix (prepared by the sol–gel method) doped with chlorophyll. The gel fabrication procedure and the doping process are first described. Then the optical behaviour from ultraviolet to far infrared is analysed. Gel samples with and without chlorophyll are studied morphologically by SEM in order to determine the spatial homogeneity of the gel matrix and the chlorophyll distribution. Finally, a mathematical model is proposed for behaviour of the gel-doped absorption coefficient as a function of chlorophyll concentration. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optical properties of samarium doped zinc-tellurite glasses

Glasses with the composition, (Sm₂ O ₃) _x (ZnO)_(40-x)(TeO ₂)₍₆₀₎, were prepared by conventional melt quenching method. The density, molar volume, and optical energy band gap of these glasses have been measured. The refractive index, molar refraction and polarizability of oxide ion have been calculated by using Lorentz-Lorentz relations. Optical absorption spectra of these glasses were recorded in the range 300–700 nm at room temperature. The oxide ion polarizabilities deduced from two different quantities, viz. refractive index and optical energy band gap, agree well compared with other glasses. The nonlinear variation of the above optical parameters with respect to samarium dopant has been explained.     

银纳米颗粒-玻璃复合材料的光学性能

采用离子交换结合热处理法,制备出银纳米颗粒-硅酸盐玻璃复合材料.利用紫外-可见光 分光光度计测量吸收光谱,利用Z-scan技术测量三阶非线性光学效应.研究结果表明,离子交换的最佳温度范围为310℃-380℃,提高离子交换温度和熔盐中AgNO3浓度,延长离子交换时间,有利于在玻璃中引入更多的银离子.玻璃中引入的银离子浓度越高,高温热处理后玻璃中银纳米颗粒的体积分数越大.含铁玻璃有利于银纳米颗粒的形成.随着热处理温度的提高和时间的延长,银纳米颗粒尺寸和颗粒体积分数增大,共振吸收峰红移.通过离子交换结合热处理方法可以获得具有优良三阶非线性光学性能的银纳米颗粒-硅酸盐玻璃复合材料,其在非等离子体共振区域的三阶非线性系数可达1.16×10-10esu,其中实部为-1.15×10-10esu,虚部为1.4×10-11esu.     

Optical properties of pyrene doped polymer thin films

Thin films of pyrene in polystyrene matrix have been prepared by spin coating technique. The concentration of polystyrene is kept constant to 1 wt.% while that of pyrene dopant varied in the range 2.30×10⁻⁴-2.30×10⁻¹ wt.%. Thickness of the films was found to depend upon concentration of pyrene and varies from 90 to 782 nm. The results of X-ray diffraction analysis reveal the crystalline nature of the films. The optical properties were studied by absorption, excitation and fluorescence spectroscopy. The band gap energy of pyrene in polymer films was calculated from absorption results. A transition from monomer to excimer is observed with thickness variation of the films. The structured part of the spectrum is assigned to the monomer emission while the broad emission band is attributed to well known pyrene excimer-like emission.     

Optical properties of doped hydrogenated amorphous silicon films

The effect of doping on the reflectance and on the imaginary part of the dielectric function in the UV-visible range was investigated for a series of hydrogenated amorphous silicon films. The samples, doped with phosphorus or boron, were prepared by a reactive evaporation technique. Doping, with either p-or n-type dopants, strongly affects the spectra causing both a red shift and a decrease in peak height. Analysis of the results in terms of the oscillator strength and the excitation energy indicates that there is a decrease in the short-range order which, according to the literature, is attributed to a degree of structural disorder induced by the dopants.     

Synthesis and luminescence properties of europium doped silica thin film

Mixture of europium oxide (Eu₂O₃) nanoparticles and spin-on glass (SOG) solution without annealing exhibited a strong room temperature photoluminescence (PL) at 610 nm. We developed a one-step synthesis to incorporate europium ions in silica thin film by mixing the Eu₂O₃ nanoparticles with the SOG solution and found that the weight ratio of the nanoparticles and the SOG solution was 1:5 for maximum PL. We also studied the temperature effect on the light emission of the europium doped thin film by time-of-flight secondary ion mass spectrometry (SIMS). The PL intensity of the thin film doubled after annealing. SIMS study confirmed the reduction of hydroxyl groups and explained the PL enhancement in the annealed europium doped silica thin film.     

The properties of epoxy resin coated silica fillers composites

Epoxy resin coated silica fillers composites with high percentage of filler loading, such as 80 to 95 vol.% are able to be produced by a mechanical mixing technique. The advantages of high filler loading of theses materials are noted from the thermal and flexural modulus. Apparently, the materials exhibit low coefficient of thermal expansion (CTE) at as low as or below 10 ppm/°C and high flexural modulus of above 20 GPa. In general, these promising characteristics fulfill the requirement to be used as substrate materials in electronic packaging applications.     

Optical properties of lead-tellurite glasses doped with samarium trioxide

The optical properties of a new family of xSm₂O₃-(40-x)PbO-60TeO₂ glasses are investigated. The optical absorption spectra were recorded at room temperature in the UV-visible region. From the absorption edge studies, the values of optical bandgap energies have been evaluated. The refractive index, molar refraction and polarizability of oxide ions have been calculated by using Lorentz-Lorentz relations. The non-linear variations of the above optical parameters are discussed with respect to samarium concentration.     

Optical properties and potential applications of doped semiconductor nanoparticles

Recent studies on the optical properties, in particular, luminescence, of a variety of doped semiconductor nanoparticles are reviewed. The effects of quantum confinement, temperature and pressure on luminescent properties are discussed. In addition, electroluminescence, cathodoluminescence, magnetoluminescence and related applications involving doped semiconductor nanoparticles are presented. A new phenomenon, upconversion luminescence of doped nanoparticles, is reviewed and its potential applications are discussed. While more research efforts are necessary in order to fully understand the fundamentals and explore the great technological potential behind doped nanoparticles, recent results already show that this is a new and exciting field with applications in many areas. In particular, the emerging field of "spintronics", where spin states are exploited in analogy to conventional electronic states, is discussed and the advantages of using doped semiconductor nanoparticles are elucidated.     

Electrical properties of multiwalled carbon nanotube reinforced fused silica composites

Multiwalled carbon nanotube (MWCNT)-fused silica composite powders were synthesized by solgel method and dense bulk composites were successfully fabricated via hot-pressing. This composite was characterized by XRD, HRTEM, and FESEM. MWCNTs in the hot-pressed composites are in their integrity observed by HRTEM. The electrical properties of MWCNT-fused silica composites were measured and analyzed. The electrical resistivity was found to decrease with the increase in the amount of the MWCNT loading in the composite. When the volume percentage of the MWCNTs increased to 5 vol%, the electrical resistivity of the composite is 24.99 omega cm, which is a decrease of twelve orders of value over that of pure fused silica matrix. The electrical resistivity further decreases to 1.742 omega. cm as the concentration of the MWCNTs increased to 10 vol%. The dielectric properties of the composites were also measured at the frequency ranging from 12.4 to 17.8 GHz (Ku band) at room temperature. The experimental results reveal that the dielectric properties are extremely sensitive to the volume percentage of the MWCNTs, and the permittivities, especially the imaginary permittivities, increase dramatically with the increase in the concentration of the MWCNTs. The improvement of dielectric properties in high frequency region mainly originates from the greatly increasing electrical properties of the composite.     

Optical properties of planar polymer waveguides doped with organo-lanthanide complexes

Lanthanide complexes, Eu(dbm)₃(Phen), [Et₄N][Eu(nta)₄] and Er(dbm)₃(Phen), are employed as luminescent dopants within planar waveguides based on a UV-processable fluorinated polymer material. Thin films doped with each of the complexes are fabricated and their spectroscopic properties investigated in detail. The films act as low loss multi-mode planar waveguides capable of guiding visible and near infrared light emitted following optical excitation of the lanthanide dopants. Judd–Ofelt parameters are calculated for the europium complex dopants and effects of the polymer host environment on the photophysical properties of the chelates are identified. The radiative properties of the europium complexes are also determined viz. their potential for use in optical amplification applications.