Continuous preparation of decorated nano zinc oxide organic sols with intense luminescence

A sort of decorated nano ZnO organic sols have been successively prepared by pulsed laser ablation at the interface of ZnO target and a flowing liquid containing polymers. It is found that the decorated nano ZnO ethanol sols, the decorated nano ZnO-PS (polystyrene) cyclohexane sols and the decorated nano ZnO-PMMA (polymethyl methacrylate) ethyl butyrate sols all have strong fluorescence emission at 329 nm and 411 nm, 308 nm and 317 nm, and at 330 nm and 400 nm, respectively. The results show the decorating for nano ZnO will intensely affect their luminescence, and the wavelength and intensity of luminescence can be adjusted or controlled by the different decoration.     

Near infrared and blue cooperative emissions in Yb-doped GeO2-PbO glasses

In previous years there has been great interest in new materials for photonic devices operating at infrared (IR) and visible (VIS) regions. We report here near infrared and blue cooperative luminescence properties for Yb³⁺-doped GeO₂-PbO glasses. Luminescence and lifetime measurements in the VIS and near-IR regions were performed to investigate the spectroscopic characteristics of the glasses. Intense emissions around 507 and 1010 nm were observed using 980 and 808 nm excitation, respectively. The VIS lifetimes (∼0.4 ms) are about half of their respective near infrared ones (∼0.8 ms), as expected for materials in which the VIS emission is caused by the cooperative effect. Regarding the IR emission, the glasses exhibited a high absorption cross-section (1.2 × 10⁻²⁰ cm²) at 978 nm and an emission cross-section of 0.6 × 10⁻²⁰ cm², at 1010 nm, with a minimum pump intensity of 2.8 kW/cm². These results suggest this glass composition as a potential material to be used in devices operating in the VIS and IR spectral range, such as 3-D displays and infrared lasers.     

Synthesis and Judd-Ofelt analysis of a sol-gel material doped with a Ln2(Benzoate)6(Phen)2 (Ln = Er/Yb) complex

In this work, we have prepared a sol-gel derived hybrid material directly doped with Er_1.4Yb_0.6(Benzoate)₆(Phen)₂ (Phen = 1,10-phenanthroline) complex, which was reported with intramolecular Yb-Er energy-transfer process in our previous work. The infrared (IR) spectra of the pure complex and hybrid gel material were investigated. The NIR photoluminescence (PL) spectrum of hybrid gel material shows strong characteristic emission of Er³⁺ with broad full width at half-maximum (FWHM) of 70 nm. Judd-Ofelt theory was used in order to analyze the optical properties of Er³⁺ ions in the hybrid gel material.     

Growth kinetics of SiGe/Si superlattices on bulk and silicon-on-insulator substrates for multi-channel devices

We have studied in reduced pressure chemical vapor deposition the growth kinetics of Si and Si_0.8Ge_0.2 on bulk Si(0 0 1) and on silicon-on-insulator (145 nm buried oxide/20 nm Si over-layer) substrates. For this, we have grown at 650 °C, 20 Torr 19 periods (Si_0.8Ge_0.2 19 nm/Si 32 nm) superlattices on both types of substrates that we have studied in secondary ion mass spectrometry, X-ray diffraction and cross-sectional transmission electron microscopy. The Si and SiGe growth rates together with the Ge content are steady on bulk Si(0 0 1), with mean values around 9.5 nm min⁻¹ and 20.2%, respectively. In contrast, growth rates decrease from ∼9.5 nm min⁻¹ down to values around 7.0 nm min⁻¹ (SiGe) and 6.3 nm min⁻¹ (Si), when the deposited thickness on SOI increases from 0 up to slightly more than 100 nm. They then go back up to values around 8.8–9.0 nm min⁻¹ as the thickness increases from 100 up to 400 nm. They then slowly decrease to values around 8.4–8.6 nm min⁻¹ as the thickness increases from 400 up to 800 nm. The Ge concentration follows on SOI exactly the opposite trend: an increase from 19.9% (0 nm) up to 20.6% (∼100 nm) followed by a decrease to values around 20.1% (400 nm) then a slow re-increase up to 20.4% (800 nm). These fluctuations are most likely due to the following SOI surface temperature variations: from 650 °C down to 638 °C (100 nm), back up to 648 °C (400 nm) followed by a slow decrease to 646 °C (800 nm). These data curves will be most useful to grow on conventional SOI substrates large number of periods, regular Si/Si_0.8Ge_0.2 superlattices that will serve as the core of multi-channel or three-dimensional nano-wires field effect transistors.     

Epitaxial films of metals from the platinum group (Ir,Rh, Pt and Ru) on YSZ-buffered Si(1 1 1)

In the present work we have grown twin-free single crystal metal films of iridium (Ir), rhodium (Rh), platinum (Pt) and ruthenium (Ru) on silicon (1 1 1) substrates via an yttria-stabilized zirconia (YSZ) buffer layer. A prerequisite for the realisation of heteroepitaxial metal films without additional texture components was the twin-free deposition of the YSZ films by pulsed laser deposition (PLD). For the metal films on top, a novel two-step growth process was applied with an extremely low deposition rate for the first 20 nm. For all metals, a drastic texture improvement by up to a factor of 9 could be observed compared to the oxide buffer layer. Minimum values were 0.18° (Ir) and 0.12° (Rh) for tilt and twist, respectively. For all four metals investigated, twin-free epitaxial films could be grown on YSZ/Si(1 1 1) whereas the twinning problem for platinum films was solved by decoupling the Pt-YSZ interface via an additional iridium interlayer. The grown metal/YSZ/Si(1 1 1) multilayer samples offer the possibility to integrate a variety of interesting nanostructures and functional materials on silicon. They are now available in 4 in wafer size.     

Synthesis and characterization of ilmenite NiTiO3 and CoTiO3 prepared by a modified Pechini method

Powders of ilmenite structure NiTiO₃ and CoTiO₃ were prepared by a simple method based on the modified Pechini process. The raw compounds and citric acid (CA) were mixed in ethanol (EA) with the molar ratio Ni(Co)/Ti/CA/EA = 1/1/1/7.5. The DTA curve shows exothermic peaks only around 300-350 °C and 600 °C, which correspond to the decomposition of the organic compound and direct crystallization of the ilmenite phase. X-ray diffraction patterns indicated that the ilmenite phase was successfully synthesized as the Ni(Co)-Ti precursor calcined above 600-900 °C for 3 h, and the activation energies of NiTiO₃ and CoTiO₃ were calculated to be about 8.84 and 13.23 kJ/mol. TEM bright field images showed that the grain sizes of powders of NiTiO₃ and CoTiO₃ at 600-900 °C were estimated to be about 10-250 and 20-200 nm depending on the nature of the aggregate. The samples of NiTiO₃ calcined at 600-800 °C have the larger specific surface area of 31.51, 18.78, and 6.01 m²/g, respectively. The UV-Vis diffuse reflectance spectra show the optical band gaps of NiTiO₃ and CoTiO₃ as 3.02 and 2.43 eV.     

Different substrate materials effect on structure of ta-C films by Raman spectroscopy for magnetic recording sliders

Raman spectra, using visible (514 nm) and ultraviolet (244 nm) excitation, of tetrahedral amorphous carbon (ta-C) films of thickness of 5 nm have been studied as a function of different substrates materials. These materials are Fe-Co (Fe: 67 at.%, Co: 33 at.%) alloy, Fe-Ni alloy (Fe: 18 at.%, Ni: 82 at.%), Au and Al₂O₃-TiC (Al₂O₃: 64 at.%, TiC: 36 at.%), which are mainly used in magnetic recording sliders. The spectra show that the films deposited on Al₂O₃-TiC contain the highest sp³ content, with a lower sp³ content observed in films deposited to Fe-Co and Fe-Ni alloys. The lowest sp³ content was observed in films on the Au substrate. The results also indicate that the anti-wear performance of ta-C film on different substrates varies as Al₂O₃-TiC (the best) > Fe-Co and Fe-Ni alloy > Au (the worst). Also mechanisms are proposed to explain the effect of substrate material on these thin film properties.     

Optical properties of Ho-doped alumino-germano-silica glass optical fiber

We present the optical characteristics of Ho-doped alumino-germano-silica glass fiber prepared by the Modified Chemical Vapor Deposition (MCVD) technique. Strong absorption peaks were observed at 1153 nm, 890 nm, 653 nm and 551 nm and another peak around 1726 nm. A possibility of lasing in the Ho-doped alumino-germano-silica glass fiber is shown by the Judd-Ofelt analysis predicting the multiple visible emissions around 550 nm and 650 nm and near infra red emissions around 1050 nm and beyond 1726 nm.     

Preparation of organic-inorganic nano-composites for antireflection coatings

In this research, bi-layer thin film stacks that served as an antireflective coating were developed. The top layer was synthesized using tetraethoxysilane and 3-(trimethoxysilyl) propyl methacrylate by the well-known sol-gel technique. Its refractive index was lower than that of the bottom layer, which was prepared by reaction between tetrabutoxyltitanium and γ-glycidoxy propyl trimethoxysilane. Antireflective coatings were obtained by spin-coating of the synthesized sols on a glass substrate, followed by pre-drying, UV-curing, and post-baking. Fourier transform infrared spectrometer was employed to investigate the evolution of chemical bonds during the UV-curing and the sol-gel processes. The size of the inorganic/organic hybrid particles in the sol was found to be less than 10 nm, as measured by transmission electron microscope and dynamic light scattering. Thermo gravimetric analyzer was used to find out the thermal degradation temperature of the two layers and the effect of post-baking. The results indicated that the thermal stability increased after post-baking at 200 °C for 15 min. The reflectance of the antireflection coating was controlled by the relative refractive indices and the thickness of the top and bottom layers. Under optimal synthesis condition, we obtained an antireflection coating, exhibiting a low reflection, 1% at 550 nm, in the visible range.     

Preparation and optical properties of transparent zirconia sol-gel materials

The optical properties of zirconia sol-gel glasses, prepared from zirconium butoxide with organic modifying agents using different ways of preparation are described. The gels obtained are characterized with UV/Vis/NIR reflectance and transmission spectroscopy between 220 nm and 2600 nm, X-ray diffraction, SEM microscopy and IR spectroscopy. The optical band gap of the amorphous gels depends on the presence of complex forming modifying agents such as acetic acid and acetylacetone and varies between 4.84 eV and 2.97 eV, respectively. Complex formation between zirconium and acetylacetone starts in the sol and is characterized by a strong peak in the UV region at about 285 nm which changes during gelation. It is shown that samples, prepared without protection agents (acetic acid or acetylacetone) display a typical granulated microstructure while gels, obtained by addition of organic additives display a flat and compact surface.     

Characterization of SBA-15 doped (PEO + LiClO4) polymer electrolytes for electrochemical applications

SBA-15 mesoporous material was prepared by the simple hydrothermal process and added to poly(ethylene oxide) (PEO) and lithium percholorate (LiClO₄) as a filler. X-ray Diffractometry (XRD), Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) were used to determine the characteristics of the composite polymer electrolyte. The SEM of the electrolyte containing 10 wt% of SBA-15 confirms the highest miscibility and amorphous nature. SBA-15 doped (PEO + LiClO₄) polymer electrolytes have shown improved conductivity over the pure PEO and (PEO + LiClO₄) electrolyte. The mesoporous SBA-15 acted as crystal cores and fined the crystallites thus decreasing the crystallinity, which provided a much more continuous amorphous domain for Li⁺ ions to move easily in the (PEO + LiClO₄) electrolyte.     

Synthesis and characterization of visible light responsive N-TiO2 mixed crystal by a modified hydrothermal process

N doped TiO₂ with anatase and rutile mixed crystal were prepared by using tetrabutyl titanate as the precursor via a modified hydrothermal process and calcination at 320 °C. The microstructure and morphology of samples were characterized by XRD, UV-vis-DRS, FTIR and XPS. The results showed that N-TiO₂ particles were crystallized to anatase and rutile mixed crystal structure; they were presented narrow particle size distribution, and the average particle size was ca. 13.5 nm calculated from XRD results. It was found that the N-doped TiO₂ particles showed strong visible-light absorption and high photocatalytic activity for the mineralization of Rhodamine B under irradiation by visible light (400-500 nm). The high visible-light photocatalytic activity of the obtained N-doped TiO₂ might result from the synergetic effect of nitrogen doping and the mixed lattice structure of N-TiO₂. Possible mechanism of N-TiO₂ mixed crystal formed under hydrothermal conditions was discussed.     

Spectroscopic properties of Er-doped Na2O-Sb2O3-B2O3-SiO2 glasses

Spectroscopic properties of Er³⁺-doped Na₂O-Sb₂O₃-B₂O₃-SiO₂ glasses have been investigated for developing 1.5-μm broadband fiber amplifiers. An intense 1.5-μm near infrared emission with a broad full width at half maximum (FWHM) of 88 nm has been obtained for Er³⁺-doped 5Na₂O-20Sb₂O₃-35B₂O₃-40SiO₂ glass upon excitation with a 980 nm laser diode. The obtained emission cross-section of the ⁴I_13/2 → ⁴I_15/2 transition and the lifetime of the ⁴I_13/2 level of Er³⁺ ions are 6.8 × 10⁻²¹ cm² and 0.36 ms, respectively. It is noted that the product of the emission cross-section and the FWHM of the glass, σ_e × FWHM, is as great as 598.4 × 10⁻²¹ cm² nm, which is comparable or higher than that of Er³⁺-doped bismuth-based and tellurite-based glasses. These special optical properties encourage in identifying them as important materials for potential applications in high performance optics and optical communication networks.     

Deposition of mechanically hard amorphous carbon nitride films from decomposition of BrCN. Effects of substrate cooling and pulsed rf-bias voltage

Mechanically hard amorphous carbon nitride films were formed by applying a combination of radio frequency (RF) bias voltage to the substrate and the chemical vapor deposition process using the decomposition reaction of BrCN with the microwave discharge flow of Ar. Cooling water was circulated inside the substrate stage. The maximum hardness was (17 ± 1) GPa for the film prepared under the negative RF bias voltage, −V_RF, of 30 V. This hardness was nearly twice that of the film prepared without cooling, suggesting that substrate cooling was effective for suppressing the relaxation of the internal stress of the film due to the temperature rise during the application of the RF bias voltage. Under the continuous operation of the RF bias voltage, films cannot be formed for −V_RF > 40 V because of the sputtering by the bombardment of energetic Ar⁺. Then, the RF bias voltage was applied with a pulsed operation. By using this operation films were prepared in the range of −V_RF = 40-100 V. The hardness, (36 ± 10) GPa, was obtained for the film obtained under the conditions of −V_RF = 100 V, the pulse period of 1000 s, and the pulse-on time of 800 s. The observed hardness scattered largely for the different observation points within this film; a single observation point in that film showed the maximum hardness of 46 GPa. According to the IR spectra of the films, the three-dimensional C-N network structure was developed.     

Influence of heat treatment on spectroscopic properties of Er in multicomponent ZrF4-ZnF2-AlF3-YF3-MF2 (M = Ca, Sr, Ba) based glass

Er³⁺ doped multicomponent fluoride based glass was prepared. These precursor fluoride glass samples were then heated using different schedules. Crystalline phase particles were successfully precipitated in the multicomponent fluoride glass samples after heat treatment. The influence of heat treatment on the spectroscopic properties of Er³⁺ in multicomponent fluoride based glass samples were discussed. Small changes of the Judd-Ofelt parameters Ω_i (i = 2, 4, 6) were found in multicomponent fluoride glass samples before and after heat treatment compared to oxyfluoride telluride glass. Preparation conditions used to produce transparent multicomponent fluoride glass ceramics doped with rare-earth ions are discussed.     

Investigation of infrared emission and lifetime in Tm-doped 75TeO2:20ZnO:5Na2O (mol%) glasses: Effect of Ho and Yb co-doping

In this paper we describe fabrication and characterization of rare-earth-doped active tellurite glasses to be used as active laser media for fiber lasers emitting in the 2 μm region. The base composition is (mol%): 75TeO₂-20ZnO-5Na₂O with different concentrations of Tm³⁺, Yb³⁺ and Ho³⁺ as dopants or co-dopants. Optical properties of doped glasses were studied and pumping at 800 nm and at 980 nm were tested in order to compare the efficiency of two pumping mechanisms. Optical characterization carried out on glasses containing only Tm³⁺ ions indicated the optimum concentration of Tm₂O₃ in terms of emission efficiency as 1 wt%. The addition of 5 wt% of Yb₂O₃ to Tm³⁺-doped glasses led to the best results in terms of intensity of fluorescence emission and of lifetime values. Yb and Ho co-doped Tm-tellurite glass was measured in emission.     

Studies of Er doped germanate-oxyfluoride and tellurium-germanate-oxyfluoride transparent glass-ceramics

An erbium doped germanate-oxyfluoride glass 60GeO₂ · 20PbO · 10PbF₂ · 10CdF₂ (GPOF) and a tellurium-germanate-oxyfluoride glass 30TeO₂ · 30GeO₂ · 20PbO · 10PbF₂ · 10CdF₂ (TGPOF) were prepared in the bulk form. By appropriate heat treatment of the as-prepared glasses above, transparent glass-ceramics were obtained with the formation of β-PbF₂ nanocrystals in the glass matrix confirmed by X-ray diffraction. Optical absorption and photoluminescence measurements were performed on as-prepared glass and glass-ceramics. The luminescence of Er³⁺ ions in transparent glass-ceramics revealed sub-band splitting generally seen in a crystal host. The intensity of red and near infrared luminescence significantly increased in transparent glass-ceramic compared to that in as-prepared glass. Two luminescence bands at 758 nm from ⁴F_7/2 → ⁴I_13/2 and at 817 nm from ²H_11/2 → ⁴I_13/2 transitions were observed from transparent glass-ceramic but cannot be seen from the corresponding as-prepared glass. These results are attributed to the change of ligand field of Er³⁺ ions and the decrease of effective phonon energy when Er³⁺ ions were incorporated into the precipitated β-PbF₂ nanocrystals.     

Energy transfer between Tm and Er ions in a TeO2-based glass pumped at diode laser wavelength

In this paper we investigate the energy transfer processes in Tm³⁺/Er³⁺ doped telluride glass pumped at the commercial diode laser pump wavelength ∼800 nm. Tailoring the rare-earths content in the glass matrix, seven main energy transfer channels within the doping range considered were identified. A 6-fold enhancement of the Er³⁺ visible frequency upconversion fluorescence at ∼660 nm is observed due to the inclusion of Tm³⁺ ions. This is evidence of the relevant contribution of the route Er₁(⁴I_11/2) + Er₂(⁴I_13/2) → Er₁(⁴I_15/2) + Er₂(⁴F_9/2) to the process. Energy migration among pumped ⁴I_9/2 level reducing the efficiency of the upconversion emission rate (³H_11/2, ⁴S_3/2, and ⁴F_9/2) is observed for Er³⁺ above 1.5 wt%. The rate equations regarding the observed energy transfer routes are determined and a qualitative analysis of the observed processes is reported.     

Sol–gel preparation and photoluminescence properties of Ce-activated Y3Al5O12 nano-sized powders

Trivalent cerium-doped yttrium aluminum garnet (YAG:Ce³⁺) nanoparticles were successfully prepared by a facile sol–gel technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were used to characterize the as-prepared phosphors. Well-crystallized fine nanoparticles were obtained at 1000 °C. Single-crystal nanoparticles with irregular shapes were obtained, with crystallite sizes ranging between 20 and 60 nm. PL intensity of the particles increased monotonically with decreasing Ce doping concentration and showed the maximum value at 0.1 at%.     

Silica aerogels prepared via rapid supercritical extraction: Effect of process variables on aerogel properties

We have examined experimentally the effects of rapid supercritical extraction (RSCE) process variables and their resulting pressure and temperature characteristics on aerogel properties. We employ an RSCE process that uses a hydraulic hot press to seal and heat a contained mold until the aerogel precursors reach a supercritical state. After a short stabilization period the hot press restraining force is lowered and the supercritical fluid is allowed to escape, leaving behind an aerogel monolith. The entire process can be accomplished in fewer than 3 h. To control the process, we set the restraining force, the maximum temperature, the heating and cooling rates, the pressure release rate and the mold volume fill ratio (related to the amount of initial precursor material). To investigate the effects of these variables we made silica aerogels from a TMOS-based recipe. We varied the volume of precursor material from 10 to 15 mL (60-97% fill volume), the restraining force from 43 to 111 kN, the temperature heat rate from 0.7 to 4.2 °C/min, the maximum temperature from 288 to 371 °C and the pressure release rate from 0.23 to 0.66 MPa/min. The RSCE process is robust. We were able to make transparent, monolithic aerogels under almost all conditions with little effect on the resulting aerogel properties. Typical density measurements yielded values of approximately 0.065 g/mL (bulk) and 1.9 g/mL (skeletal). The samples were translucent and transmitted 70% of the light at 800 nm (for 5-mm thick samples). The BET surface areas ranged from 517 to 590 m²/g. Maximum temperature was the only variable found to have a significant effect on the aerogels’ properties. As the maximum temperature increased from 288 to 371 °C the surface area decreased from 560 to 395 m²/g and average pore diameter (BJH desorption) increased from 21 to 32 nm.