Search results for "EXCITATION"
showing 10 items of 1290 documents
Optical activation of a silicon vibrating sensor
1986
The operation of a micromachined silicon vibrating sensor with both optical excitation and optical interrogation is reported. The proper locations at which the optical excitation should be applied for optimum excitation of different modes of resonance are described.
Visible luminescence peculiar to sintered silica nanoparticles: Spectral and decay properties
2015
We report that the sintering at 1000 degrees C of silica nanoparticles (an average diameter of 14 nm) produces a transparent sample that exhibits a bright visible emission under UV excitation. The use of time resolved luminescence spectroscopy and a tunable laser source allows us to single out three contributions centered at 1.96 eV, 2.41 eV and 3.43 eV. The excitation spectra of these emissions evidence bell shaped bands consistent with transitions between localized defects' states. For each emission we study the intensity and the lifetime in the temperature range from 300 K down to 10 K, thus evidencing the competition between radiative and non-radiative processes in the optical cycle of …
Experimental dynamic analysis of elastic-plastic shear frames with secondary structures
2003
Various experimental models are developed to study the influence of lightweight secondary structures on the dynamic response of elastic and elastic-plastic shear frames. Small-scale two-story model frames, with an elastic single-degree-of-freedom secondary structure attached, are considered for sinusoidal and random in-plane support excitation. Both elastic and elastic-plastic responses are recorded by varying the material properties of the columns of a distinguished floor. Parametric studies are performed by varying the secondary structure's fundamental frequency and damping. Experimental results are compared with those obtained by computational simulations. Experimental and numerical resu…
Electron Binding in a Superatom with a Repulsive Coulomb Barrier: The Case of [Ag44(SC6H3F2)30]4– in the Gas Phase
2020
The electron binding mechanism in [Ag44(SC6H3F2)30]4- (SC6H3F2 = 3,4-difluorobenzenethiolate) tetra-anion was studied by photoelectron spectroscopy (PES), collision-induced dissociation mass spectrometry (CID-MS), and density functional theory (DFT) computations. PES showed that [Ag44(SC6H3F2)30]4- is energetically metastable with respect to electron autodetachment {[Ag44(SC6H3F2)30]3- + e-} and features a repulsive Coulomb barrier (RCB) with a height of 2.7 eV. However, CID-MS revealed that [Ag44(SC6H3F2)30]4- does not release an electron upon collisional excitation but undergoes dissociation. DFT computations performed on the known structure of [Ag44(SC6H3F2)30]4- confirmed the negative a…
Femtosecond exciton dynamics in WSe2 optical waveguides
2020
Van-der Waals (vdW) atomically layered crystals can act as optical waveguides over a broad range of the electromagnetic spectrum ranging from Terahertz to visible. Unlike common Si-based waveguides, vdW semiconductors host strong excitonic resonances that may be controlled using non-thermal stimuli including electrostatic gating and photoexcitation. Here, we utilize waveguide modes to examine photo-induced changes of excitons in the prototypical vdW semiconductor, WSe2, prompted by femtosecond light pulses. Using time-resolved scanning near-field optical microscopy we visualize the electric field profiles of waveguide modes in real space and time and extract the temporal evolution of the op…
Optical studies of Y3(Al,Ga)5O12:Ce3+,Cr3+,Nd3+ nano-phosphors obtained by the Pechini method
2019
The Y-3(Al,Ga)(5)O-12:Ce3+,Cr3+,Nd3+ (YAGG) nano-phosphors with homogeneous particle-size distribution, low aggregation and average crystalline size of about 65 nm were obtained using a modified Pechini method. Only slight aggregation of the crystallites occurs after post-annealing at 1100 degrees C. The intense Ce3+ bands in the excitation spectra of the Ce3+,Cr3+,Nd3+ co-doped materials monitoring the Cr3+ emission at 690 nm indicate energy transfer from Ce(3+ )to Cr3+. Weak Nd3+ lines are observed, as well. In addition, the emission of Nd3+ at 1060 nm with excitation of Ce3+ and Cr3+ confirms the Ce3+/Cr3+ to Nd3+ energy transfer. The short average luminescence decay times for the Ce3+ e…
Relaxation of photogenerated carriers in P3HT:PCBM organic blends.
2009
Relaxing in the sunlight. Long time-transient decays of photogenerated carriers in P3HT:PCBM blends for organic solar cells are interpreted in terms of the relaxation of hole carriers in a broad density of states. The after-pulse time-resolved microwave conductivity (TRMC) decays observed in P3HT:PCBM blends display a dependence on time close to t−β, independent of excitation intensity, in the 10 ns–1 μs range. This is explained in terms of the relaxation of carriers in a Gaussian density of states (DOS). The model is based on a demarcation level that moves with time by thermal release and retrapping of initially trapped carriers. The model shows that when the disorder is large the after-pu…
Oscillator strengths of sulphur 3s23p34s3So-3s23p34p3P transitions measured by time resolved two-photon laser spectroscopy
1997
Oscillator strengths for the three 3s23p34s 3S1o-3s23p34p 3P0,1,2 transitions in neutral sulphur have been determined directly from lifetime measurements. Two-photon UV laser excitation and subsequent fluorescence detection have been used on atoms produced in a thermal sulphur beam or in a laser-driven plasma. A good agreement was found between data obtained in both schemes. The lifetime data obtained, τ(3P0) = 46.1(1.0) ns, τ(3P1) = 46.1(1.0) ns and τ(3P2) = 46.1(1.0) ns are compared with results of theoretical and experimental data from literature. The absorption oscillator strengths derived are f(3S1o-3P0) = 0.120(0.003), f(3S1o-3P1) = 0.360(0.008) and f(3S1o-3P2) = 0.600(0.013), respect…
Symmetry of valence states of Heusler compounds explored by linear dichroism in hard-x-ray photoelectron spectroscopy.
2011
This study reports on the linear dichroism in angular-resolved photoemission from the valence band of the Heusler compounds ${\mathrm{NiTi}}_{0.9}{\mathrm{Sc}}_{0.1}\mathrm{Sn}$ and NiMnSb. High-resolution photoelectron spectroscopy was performed with an excitation energy of $h\ensuremath{\nu}=7.938\text{ }\text{ }\mathrm{keV}$. The linear polarization of the photons was changed using an in-vacuum diamond phase retarder. The valence band spectra exhibit the typical structure expected from first-principles calculations of the electronic structure of these compounds. Noticeable linear dichroism is found in the valence band of both materials, and this allows for a symmetry analysis of the cont…
Upconversion luminescent nanoparticles in physical sensing and in monitoring physical processes in biological samples.
2015
The most frequently used strategy for sensing is based on the emission variation of a photoactive system and it can be classified as chemical or physical depending on its response to either a chemical or a physical stimulus. There are a large number of luminescent nanomaterials that respond to chemical species, but comparatively, with the exception of temperature sensing, to date there are few examples showing the capacity of photoactive nanosystems responsive to physical stimuli, such as magnetic and electric fields, high radiation energy, tension/pressure, viscosity, etc, and very few of them comprise upconversion nanoparticles (UCNPs). These nanomaterials consist of an inorganic matrix d…