Development of the FTIR properties of nano-structure silica gel doped with different rare earth elements,prepared by sol-gel route

Structural characteristics of pure silica gel (silica-xerogel, SiO₂) and silica gel doped with some rare earth elements (REEs) such as, praseodymium Pr³⁺, and Europium Eu³⁺, Erbium Er³⁺ and Holmium Ho³⁺ ions, with different concentrations ranging from 1 up to 6%, in the form of monolith materials were prepared by sol-gel technique, Using tetra-ethoxysilane as precursor materials, which are of particular interest for sol-gel integrated optics applications. Some structural features of sol-gel derived monolith are analyzed, namely the structure of nano-particle momolith samples, based on X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR). We show that the XRD spectra of α-crystobalite are obtained for the pure samples at 1100°C and even by doping with the four REEs ions.     

Visible Up-Conversion Luminescence in Ho3+: BaTiO3 Nano-Crystals Prepared by Sol Gel Technique

Visible up-conversion emissions at (435, 545, 580, 675 and 690 nm) and (437, 547 575 and 675 nm) have been observed from the sol-gel derived nano-crystalline Ho³⁺: BaTiO₃ powders and thin films respectively, under 808 nm laser diode excitation emissions. Combined with the energy level structure of Ho³⁺ ions and the kinetics of the visible emissions, the up-conversion mechanism has been analyzed and explained. The blue, green and red emissions of both samples has been attributed to the ground state-directed transition from (⁵F₁), (⁵S₂) and (⁵F₅), which are populated through excited state absorption (ESA) for 808 nm excitation. Nano-structure pure barium titanate and doped with different concentrations of Ho³⁺ ions in the from of powder and thin film have been prepared by sol-gel technique, using barium acetate (Ba(Ac)₂), and titanium butoxide (Ti(C₄H₉O)₄), as precursors. The thin films were prepared by sol-gel spin coating method. The as-grown thin films and powders were found to be amorphous, which crystallized to the tetragonal phase after heating at 750°C in air for 30 minutes. The crystallite sizes of the thin film and powder both doped with 4% Ho³⁺ ions was found to be equal to 11 and 16 nm, respectvely.     

Structural and thermal properties of monolithic silica–phosphate (SiO<Subscript>2</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>) gel glasses prepared by sol–gel technique

A sol–gel process for producing monolithic silica–phosphate (SiO₂–P₂O₅) system different concentrations of P₂O₅, starting with tetra-ethoxysilane TEOS, and triethyl-phosphate as sources of SiO₂ and P₂O₅ was performed. The gels were heat-treated at temperatures ranging from 100 up to 900 °C. The structural and chemical analyses of the samples were determined by using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). It was found from the XRD that the existence of phosphorus enhances the crystallization of silica gel, while the FTIR indicated the main functional groups of silica–phosphate. It is important to study the effect of hydroxyl in silica–phosphate glass. The results obtained are promising to use the prepared samples in a variety of applications, ranging from traditional application such as lighting products) to the modern application (such as optical fibers. Optical studies were measured by using the spectrophotometer in wavelength range 0.2–2.5 μm. The refractive index (n) was calculated for the prepared samples, it was found to be strongly affected by structural rearrangement resulting from the elimination of the solvent and the Si–OH, Si–O–Si and Si–O–OH bonding by phosphate and aluminum and it increases by increasing phosphate concentrations. The weight losses have investigated for prepared samples.     

Structure and dielectric studies of nano-composite Fe2O3: BaTiO3 prepared by sol-gel method

Nano-structure pure barium titanate (BaTiO₃) and that was doped with iron oxide (Fe₂O₃), have been prepared by sol-gel method, using barium acetate (Ba(Ac)₂) and titanium butoxide (Ti(C₄H₉O)₄), as precursors. The as-grown prepared samples by sol-gel technique were found to be amorphous, which crystallized to the tetragonal phase after synthesized at 750 °C in air for 1 h as detected from the XRD patterns. The XRD data were confirmed by transmission electron microscope (TEM). The dielectric properties namely; dielectric constant (ε′) and loss tangent (tan δ) in the frequency range between 42 Hz and 1 MHz, at range of temperature 25-250 °C were investigated. The temperature dependence of ε′ and tan δ for the undoped and doped materials, at 1 kHz, was also investigated. As a result, tan δ increased rapidly with decreasing temperature below 125 °C (Curie temperature) while above this temperature, tan δ shows temperature independent. As a result, below and above Curie temperature, ferroelectric phase and paraelectric phase of BaTiO₃ can be obtained, respectively.     

Detection of up-conversion in nano-structure BaTiO<Subscript>3</Subscript> co-doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> ions

Nano-structure pure barium titanate BaTiO₃ (BT) and (BT) co-doped with constant concentration of Er³⁺ ions and different concentrations of Yb³⁺ ions were prepared using sol–gel method. XRD results confirmed that the pure sample was found to crystallize in tetragonal phase by sintering at 750 °C for 1 h. All major peaks corresponding to perovskite BT phase appeared. Efficient infrared-to-visible up-conversion is reported in the doped samples. The conversion process and results in the generation of visible emissions are discussed. Up-conversion efficiency for red emission predominates in doped samples. Results illustrate the large potential of this class of materials for photonic applications in optoelectronics devices.     

Synthesis of Fe2O3 concentrations and sintering temperature on FTIR and magnetic susceptibility measured from 4 to 300 K of monolith silica gel prepared by sol–gel technique

Nano-crystalline ferric oxide was synthesized inside an amorphous silica matrix by the sol–gel method. The formation of ferric oxide can be detected, giving fine particles around 5–10 nm crystallite sizes calculated from win-fit program. This is associated with a specific role of the silica matrix, which facilitates the diffusion of the reacting cations, enhancing the ferric oxide formation. γ- to α- and/or ε-Fe₂O₃ transformations take place by increasing the Fe₂O₃ concentration for samples sintering at constant-heat treatment temperature. The dried monolith gel materials were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), as well as by scanning electron microscopy (SEM). The magnetic susceptibility at zero-field cooling (M_ZFC) of the prepared samples was evaluated using superconducting quantum interference device (SQUID) magnetometer in temperature range from 4 to 300 K at 1 T.     

Structural and Photoluminescence Behaviors of Nano-Structure Thin Film and Bulk Silica Gel Derived Glasses

Nano-structure bulk and thin film silica gel derived glasses were prepared by sol-gel technique. Both samples were derived from the same precursor and subjected to the same heat-treatment regime. Structural information about prepared samples are obtained by analyzing the XRD patterns and TEM micrographs. The bulk samples phase changes from amorphous to -crystoballite at higher temperature (1300°C) than that in the thin film (500°C). The crystallite size depends to a large extent on the heat-treatment temperature. Bulk sample heat treated at 1400°C was as small as 10.4 nm. Thin film samples show higher response to heat-treatment temperature than the bulk samples, where the film is denser, has smaller pores and seems more homogeneous at lower temperature than bulk sample as revealed by SEM. The observed Raman spectra for bulk and thin film samples are in accordance with that of the -crystoballite. The Raman peak intensity is higher for thin film than bulk samples. The photoluminescence PL measurements for bulk samples show a broad intense peak at 532 nm combined with three weak peaks at longer wavelength 587, 635 and 666 nm. The PL peak intensity shows a reasonable decrease with increasing the heat-treatment temperature while the peak position shifted slightly to a lower wavelength. While the thin film samples show a unique peak at wavelength = 523 nm. The appearance of PL bands are interpreted on the light of non-bridged oxygen hole center as well as the structure defects.     

Effect of elevated concentrations of strontium and iron on the structural and dielectric characteristics of Ba(1−x−y)Sr(x)Ti Fe(y)O3 prepared through sol–gel technique

Nano-composite Ba_1−xSr_(x)TiO₃ (BST), where x=0.01–0.50 and doped with different concentrations of iron Ba_(1−x−y)Sr_(x)TiFe _(y)O₃ (BSTF), where x=0.01 and y=0.01–0.05 powders were prepared by sol–gel method.