High Vibrational Energy Research Articles

Nd3+-doped perovskite nanosheets with NIR luminescence

Exfoliation of layered materials into ultrathin nanosheets introduces a new cost-effective and environmentally safe fabrication method for novel nanostructured devices. In the present study, we have developed for the first time inorganic oxide nanosheets with near-infrared (NIR) luminescence properties. KLa1−xNdxNb2O7 (x=0.025, 0.05, 0.1, 0.2, or 0.3) powders obtained by a solid state reaction were exfoliated into single-layer metal oxide nanosheets with approximately 1.7nm thickness by osmotic swelling with tetrabutylammonium cations, followed by the protonation of KLa1−xNdxNb2O7. We observed strong coupling of high-energy OH vibration with the Nd3+ energy levels upon protonation and exfoliation steps because of the extremely thin nature of oxide nanosheet-layers. Colloidal oxide nanosheets with an optimized Nd-doping concentration yielded detectable NIR luminescence due to 4F3/2–4I11/2 (Nd3+) radiative transitions, which opens possible application of these oxide nanosheets as bioimaging probes and bioanalytical sensors.

The Design of LED Intelligent Lighting Control System Based on CAN Bus

In order to meet the requirements of high stability, high vibration resistance, energy saving and environmental protection and long service life for the railway vehicle car lighting system, this paper designed a LED (Light Emitting Diode) lighting control system suitable for railway vehicles car. Using IPC for the principal computer, microcontroller for the subordinate computer, CAN bus as the communication network. Multiple brightness sensor collect the brightness information of car environment. According to the characteristics that the LED is suitable for high frequency switch power, using PWM technology, the current though the LED light can be control. ATmega16 microcontroller as the control core can automatically to adjust the brightness of the car according to the change of external environment, it ensured that the LED light emitting uniform and stable so that this kind of control system has very high application value.

Excited-State Structure and Dynamics of Keto–Amino Cytosine: The 1ππ* State Is Nonplanar and Its Radiationless Decay Is Not Ultrafast

We have measured the mass- and tautomer-specific S0 → S1 vibronic spectra and S1 state lifetimes of the keto–amino tautomer of cytosine cooled in supersonic jets, using two-color resonant two-photon ionization (R2PI) spectroscopy at 0.05 cm(–1) resolution. The rotational contours of the 0(0)(0) band and nine vibronic bands up to +437 cm(–1) are polarized in the pyrimidinone plane, proving that the electronic excitation is to a 1ππ* state. All vibronic excitations up to +437 cm(–1) are overtone and combination bands of the low-frequency out-of-plane ν1′ (butterfly), ν2′ (boat), and ν3′ (H–N–C6–H twist) vibrations. UV vibronic spectrum simulations based on approximate second-order coupled-cluster (CC2) calculations of the ground and 1ππ* states are in good agreement with the experimental R2PI spectrum, but only if the calculated ν1′ and ν2′ frequencies are reduced by a factor of 4 and anharmonicity is included. Together with the high intensity of the ν1′ and ν2′ overtone vibronic excitations, this implies that the 1ππ* potential energy surface is much softer and much more anharmonic in the out-of-plane directions than predicted by the CC2 method. The 1ππ* state lifetime is determined from the Lorentzian line broadening necessary to reproduce the rotational band contours: at the 0(0)(0) band it is τ = 44 ps, remains at τ = 35–45 ps up to +205 cm(–1), and decreases to 25–30 ps up to +437 cm(–1). These lifetimes are 20–40 times longer than the 0.5–1.5 ps lifetimes previously measured with femtosecond pump–probe techniques at higher vibrational energies (1500–3800 cm(–1)). Thus, the nonradiative relaxation rate of keto–amino cytosine close to the 1ππ* state minimum is k(nr) 2.5 × 10(10) s(–1), much smaller than at higher energies. An additional nonradiative decay channel opens at +500 cm(–1) excess energy. Since high overtone bands of ν1′ and ν2′ are observed in the R2PI spectrum but only a single weak 2ν3′ band, we propose that ν3′ is a promoting mode for nonradiative decay, consistent with the observation that the ν3′ normal-mode eigenvector points toward the “C6-puckered” conical intersection geometry.

Research on Powder Metallurgy High Nitrogen Stainless Steels

High nitrogen Fe-18Cr-12Mn-3Mo-xN austenitic stainless steels were prepared by mechanical alloying and powder metallurgical pressing-sintering techniques. The microstructures, nitrogen contents and sintering properties of the milled powders and sintered bodies had been also investigated. The results show that high nitrogen and nearly spherical composite powders with good compressibility can be obtained by high-energy vibration ball milling and high temperature nitriding. It is also found that the sintering temperature has a significant effect on the density and the nitrogen content of sintered specimens, and the optimal sintering temperature are determined to be 1250°C, at which a favorable combination of the relative density as high as 97.1% and the final nitrogen content of 0.79wt% in sintered specimens can be obtained. The sintered bodies mainly consist of γ-austenite, α-ferrite and the lamellar Cr2N phase. After solution-annealing at 1150°C for 1.5h followed by water-quenching, high nitrogen austenitic stainless steels reveal a fully austenitic structure.

Large scale variational calculations on the vibrational level structure and vibrational mixing in S0 HDCO up to very high excitation energies

We perform converged high precision variational calculations to determine the exact energies of all vibrational states in S0 HDCO, extending up to 10000cm−1 of vibrational excitation energy. We also explore the resonances and intermode couplings in this energy range. We compare the calculated level structure to the recently measured frequencies by Ellsworth et al. [K.K. Ellsworth, B.D. Lajiness, J.P. Lajiness and W.F. Polik, J. Mol. Spectrosc. 252 (2008) 205] in order to check their assignments and further clarify the vibrational mixing pattern and vibrational resonances in HDCO, that are very different from the other more symmetric formaldehyde species H2CO and D2CO. For the calculations we use our specific vibrational method (recently employed for extensive vibrational studies on H2CO and D2CO), consisting of a combination of a search/selection algorithm and a Lanczos iteration procedure and based on the Martin, Lee, Taylor potential energy surface for formaldehyde, allowing to extend the calculations up to very high vibrational excitation energies.

Modulation of the emission intensity and color output of NaYF4 : Yb3+,Er3+ nanocrystals by OH−

Oleic acid together with sodium hydroxide (NaOH) was widely used to control the size, phase and morphology of NaYF4 UCNCs. However, reports are scarce about the modulation of the luminescence intensity and color output of NaYF4 UCNCs by using different amounts of NaOH. Here, we synthesized NaYF4:Yb3+, Er3+ nanocrystals by a hydro/solvent thermal method using oleic acid as ligand with different amounts of NaOH and systematically investigated their upconverted fluorescence spectra. The results indicated that the emission intensity of NaYF4 : Yb3+,Er3+, especially the green emission at 540 nm was dramatically increased as NaOH decreased. The enhancement factors of 540 nm emissions were 48, 42 and 32 for samples prepared with 0 g, 0.2 g and 0.4 g NaOH (the corresponding pH of the reaction solution were 5.9, 6.9 and 7.4), respectively, compared with that of the product prepared with the usually used 0.7 g NaOH (the corresponding pH was 8.3). Importantly, the ratio of green to red (RGR) increased from 0.4 to 5.9 when the pH decreased from 8.3 to 5.9. That is to say, the color output was tuned from orange yellow to nearly pure green. This resulted from the high energy vibration of OH−, which led to nonradiative relaxation from green emission levels (2H11/2 and 4S3/2) to the red emission level (4F9/2) and nonradiative relaxation from the red emission level (4F9/2) to the no emission level (4I11/2) of Er3+.

Cu박판의 초음파 금속 용착 실험을 통한 용착성 평가

The Ultrasonic metal welding is used in the solid-phase welding method at room temperature or low temperature state. In welding process, the high frequency vibration energy is delivered to the welding part under the constant pressure for welding. In this study, we aimed to design and manufacture a 40,000 Hz band horn through finite element analysis. By performing modal analysis and harmonic response analysis, the modal analysis result is that the horn frequency was 39,599Hz and the harmonic response result that the horn frequency was 39,533Hz. These results were similar. In order to observe the designed horn`s performance, about 4,000 voltage data was obtained from a light sensor and was analyzed by FFT analysis using Origin Tool. The result RMS amplitude was approximately at 40,000Hz, and maximum amplitude was . Using this manufactured horn along with an ultrasonic metal welder and tension tester, the weldability of Cu sheets was evaluated. The maximum tensile force was 66.53 N in the welding condition of 2.0 bar pressure, 60% amplitude, and 0.32 s welding time. In excessive welding conditions, it was revealed that weldability is influenced negatively.

Surface effect of nanocrystals doped with rare-earth ions enriched on surface and its application in upconversion luminescence

By employing a certain proportion of hydrogen peroxide, ammonia, ammonium fluoride, and ethylene diamine tetraacetic acid (EDTA) as precipitator, well-crystallized LaOF:Eu3+ and LaOF:Yb3+, Er3+ nanocrystals are synthesized by using the chemical co-precipitation method. The structural properties of these samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) spectra. The results show that all the samples have an average size below 70 nm, which decreases gradually with the increase of the EDTA content, and a certain number of EDTA molecules are coupled with doped ions on the surfaces of nanocrystals. Most of the doped ions are proved to be enriched on the surfaces of nanocrystals and surrounded by the high energy vibration groups and bonds in EDTA molecules. The observed differences in upconversion emission spectrum among the different LaOF:Yb3+, Er3+ nanocrystals are explained by the different two-photon upconversion mechanisms. Especially, in the LaOF:Yb3+, Er3+ nanocrystals with EDTA, the two-photon processes that contain several special cross-relaxation processes are introduced to analyse the corresponding upconversion mechanisms.

Variational study on the vibrational level structure and vibrational level mixing of highly vibrationally excited S0 D2CO

We perform converged high precision variational calculations to determine the frequencies of a large number of vibrational levels in S0 D2CO, extending from low to very high excess vibrational energies. For the calculations we use our specific vibrational method (recently employed for studies on H2CO), consisting of a combination of a search/selection algorithm and a Lanczos iteration procedure. Using the same method we perform large scale converged calculations on the vibrational level spectral structure and fragmentation at selected highly excited overtone states, up to excess vibrational energies of ∼17000cm−1, in order to study the characteristics of intramolecular vibrational redistribution (IVR), vibrational level density and mode selectivity.

A targetable fluorescent sensor for hypochlorite based on a luminescent europium complex loaded carbon nanotube

A new europium complex covalently modified single-walled carbon nanotube (SWNT) was reported here as an emissive nanosensor for the determination of hypochlorite. FT-IR, UV-vis, TEM and SEM proved that it was successfully linked to the SWNT surface. A luminescence quenching effect of this nanoprobe was rapidly observed in the presence of ClO(-). Moreover, the quenching process can be detected within 1 s and the detection limit could reach 9 × 10(-8) M. We regarded that the ligand exchange process and the high vibration energy of the ClO(-) resulted in this selective recognition behavior.

Variational study on the vibrational level structure and IVR behavior of highly vibrationally excited S 0 formaldehyde

We perform large scale converged variational vibrational calculations on S 0 formaldehyde up to very high excess vibrational energies ( E v ), E v ∼ 17,000 cm −1, using our vibrational method, consisting of a specific search/selection/Lanczos iteration procedure. Using the same method we investigate the vibrational level structure and intramolecular vibrational redistribution (IVR) characteristics for various vibrational levels in this energy range in order to assess the onset of IVR.

Design and evaluation of highly sensitive luminescent terbium sensor for hypochlorite in water

A novel terbium 2-methyl-benzoimidazole-5-carboxylic acid complex was prepared and incorporated into silica matrix (tetraethoxysilane) using a mild sol–gel technique. We then successfully fabricated a terbium luminescent xerogel, which maintained intense green emission even in pure water. The emission was rapidly (~1 s) quenched by ClO− (detection limit 10−5 M) but not NO3 −, CH3COO−, F−, Cl−, Br−, I−, CO3 −, and OH−. The selectivity appears to be due to the high vibrational energy of ClO− as well as its strong oxidation capability.

A Novel Vibration Energy Harvesting Method via Pulse Liquid Flow

Presently the electric power harvested from vibration energy by existing researches is mostly at the level of μW or mW, which is not available for structural vibration energy harvesting due to the characteristics of lower frequency, bigger mass, and higher Vibration Energy. Therefore, a novel vibration energy harvesting method via pulse liquid flow for structural vibration is put forward. The principle of the method is mainly depicted as follows: the pulse liquid flow motivated by external vibration twirls the hydraulic motor’s output shaft; then electric power is produced by the generator rotor due to the shaft torque. In this paper, the Energy Harvesting Model has been built with the help of the fluid mechanics principle and the electromagnetic induction principle. In addition, the formula for output voltage was derived and, meanwhile, the influence of the piston’s moving speed amplitude on output voltage has been analyzed as well. Ultimately, we have designed an experimental setup in order to verify the rationality of the analytical method. In our experiments, sinusoidal mechanical excitation was used to test the Energy Harvesting characteristics by the J95-I absorber testing platform. According to the results, the waveform of output line voltage is in a good agreement with the theoretical analysis, which shows effectiveness of this novel method and the worth of which to help solve the problem of dependable power supply for current semi-active vibration control systems.

Vibrational calculations in formaldehyde: the CH stretch system

Abstract An alternative procedure for the calculation of highly excited vibrational levels in S0 formaldehyde was developed to apply to larger molecules. It is based on a new set of symmetrized vibrational valence coordinates. The fully symmetrized vibrational kinetic energy operator is derived in these coordinates using the Handy expression [Molec. Phys. 61, 207 (1987)]. The potential energy surface is expressed as a fully symmetrized quartic expansion in the coordinates. We have performed ab initio electronic computations using GAMESS to obtain all force constants of the S0 formaldehyde quartic force field. Our large scale vibrational calculations are based on a fully symmetrized vibrational basis set, in product form. The vibrational levels are calculated one by one using an artificial intelligence search/selection procedure and subsequent Lanczos iteration, providing access to extremely high vibrational energies. In this work special attention has been given to the CH stretch system by calculating the energies up to the fifth CH stretch overtone at ∼16000 cm−1, but the method has also been tested on two highly excited combination levels including other lower frequency modes.

High power density vibration energy harvester with high permeability magnetic material

An alternative design of vibration energy harvester was demonstrated to significantly increase the output power density. This design had two magnetic solenoids fixed at two sides of a spring supported hard magnet pair with anti-parallel magnetization, which produced a spatially inhomogeneous bias magnetic field for switching the flux inside the solenoids during vibration. Experimental results showed an output voltage of 2.52 V and a power density 20.84 mW/cm3 at 42 Hz, with a half peak working bandwidth of 6 Hz. This vibration energy harvester design leads to high output voltage, power and power density that are critical for real applications.

Molecular Dynamics of Carbon Nanotubes Deposited on a Silicon Surface via Collision: Temperature Dependence

We investigated how temperature influences the structural and energetic dynamics of carbon nanotubes (CNTs) undergoing a high-speed impact with a Si (110) surface. By performing molecular dynamics simulations in the temperature range of 100 - 300 K, we found that a low temperature CNT ends up with a higher vibrational energy after collision than a high temperature CNT. The vibrational temperature of CNT increases by increasing the surface temperature. Overall, the structural and energy relaxation of low temperature CNTs are faster than those of high temperature CNTs.

Preparation of white light emitting YVO4: Ln3+ and silica-coated YVO4:Ln3+ (Ln3+ = Eu3+, Dy3+, Tm3+) nanoparticles by CTAB/n-butanol/hexane/water microemulsion route: Energy transfer and site symmetry studies

Lanthanide ions (Ln3+ = Eu3+, Dy3+, Tm3+) doped YVO4 and silica coated YVO4:Ln3+ (YVO4:Ln3+@SiO2) nanoparticles have been prepared by a microemulsion route using Cetyl trimethyl ammonium bromide (CTAB)/n-butanol/hexane/water. Average crystallite sizes of YVO4:Ln3+ annealed at 500 and 900 °C are found to be ∼30 and ∼80 nm, respectively. Successful coating of the silica on the YVO4:Ln3+ core could be observed by transmission electron microscopy. The silanol group (SiO–H) is present in silica coated samples (heated up to 500 °C) and acts as luminescence quencher. The luminescence intensity and lifetime of those samples were less than those of their counterpart core samples. This has been attributed to the multi-phonon relaxation arising from high vibrational energy of the silanol group (3750 cm−1). When annealed up to 900 °C, both the luminescence intensity and the lifetime for silica coated systems increase significantly due to the loss of the silanol group, as well as the extent of reduction of surface non-radiative process at the core-shell formation. In case of triple doping (Ln3+ = Eu3+, Dy3+ and Tm3+), the emission of Dy3+ is more than that of either Eu3+ or Tm3+. This has been related to the energy transfer from Dy3+ to Eu3+ or Tm3+. Interestingly, a significant difference in the asymmetric ratio of electric dipole allowed transition to magnetic dipole allowed transition was observed when different Ln3+ ions are doped in the same host. This observation has been explained on the basis of their full width at half maximum of the emission peak. Based on the Commission Internationale d'Eclairage (CIE) coordinates calculations, only Dy3+ and triple Ln3+ doped YVO4 samples have CIE coordinates close to the ideal white light values amongst the samples. These materials could be used as potential nanophosphors for white light-emitting diodes (LEDs) applications.

Preparation of Nitrogen-Containing Stainless Steels by Vibration Milling and Cold-Press Sintering

Nitrogen-containing nickel-free Fe-18Cr-10Mn-2Mo stainless steel powders were produced by high-energy vibration ball milling under flowing nitrogen atmosphere. It can be found when milling below 4h, the nitrogen contents of the powders tend to be higher level and their particle sizes reduce with increasing the milling time, but when milling beyond 4h, the particle sizes of the powders could not be further refined and the nitrogen contents of the powders increase quite slowly. During high-energy ball milling, there is no new phase formed in the milled powders. The powders milled for 4h, whose nitrogen content is 0.42%, were cold-pressed and sintered under flowing nitrogen atmosphere. The sintered bodies have a ferrite-austenite duplex microstructure, and obtain a relative density as high as 97.2% and a final nitrogen content of 0.38%. The mechanical tensile properties of the sintered bodies are far superior to those of the nitrogen-containing stainless steel prepared by high nitrogen pressure melting technique.

High torsional vibrational energies of H2O2 and CH3OH studied by MULTIMODE with a large amplitude motion coupled to two effective contraction schemes

We have introduced the theory of the Reaction Path Hamiltonian into the variational scheme MULTIMODE, for the calculation of vibrational energy levels of polyatomic molecules which have a single large amplitude motion (for which the classic example is hydrogen peroxide). As with all MULTIMODE calculations, the greatest difficulty is the size of the CI matrix. The algorithm is now enhanced to include user-defined contraction schemes in order to probe high-energy regions of the potential energy surface. Furthermore an increased efficiency in matrix element evaluation is reported. High torsional levels of hydrogen peroxide and methanol are reported; those for hydrogen peroxide are consistent with an ‘exact’ variational procedure in valence coordinates, whilst those for methanol are predictions based on a recently-derived potential energy surface. The coupling between the torsional mode and the remaining normal modes is highlighted. These ‘technical’ advances open up the use of MULTIMODE for the study of vibrations in larger systems.

Isomerization and electronic relaxation of azobenzene after being excited to higher electronic states

In this work, some critical structures (e.g. stable structure, transition state, local minimum and conical intersection) of azobenzene photoisomerization were optimized by means of ab initio CASSCF calculation. The potential energy surfaces for the CNNC dihedral torsion and CNN bond angle concerted-inversion pathway were mapped to explore the relaxation process of azobenzene (AB) photoisomerization. The results indicate that the rotational mechanism favors the photoisomerization of the S 1(n,π*) and S 2(π,π*) trans-AB. The concerted-inversion mechanism may operate in the decay process of S 2(π,π*) or higher state trans-AB. By borrowing the (n,π*; π,π*) and (n 2,π* 2) electronic states, trans-AB upon excitation to the higher states can quickly relax to the S 1(n,π*) or ground state via the rotation or concerted-inversion pathway. The forming ground-state species with higher vibrational energy from the higher excited states will become the stable trans-isomer through the concerted-inversion pathway. These relaxation processes have been confirmed by the conical intersections calculated by the high-level CASSCF method.