Reduction Of Decay Time Research Articles

Thermally stable illuminating characteristics of Tb3+/Sm3+ ions activated BaO–SrO–Al2O3–B2O3–SiO2 glasses for photonic applications

A set of Tb3+ and Tb3+/Sm3+ co-doped barium strontium aluminium borosilicate (BaSrAlBSi) glasses were produced to examine optical properties carefully. The transparent BaSrAlBSi glass amorphous nature was established by the XRD pattern. The absorption profile demonstrates the various peaks from n-UV to NIR range caused by the Tb3+ as well Sm3+ ions in BaSrAlBSi glass. BSi:Tb1.0 glasses give intense green emission under λex = 368 nm, BSi:Sm1.0 glasses exhibit the emission spectrum caused by the transitions of the Sm3+ ions. The Tb3+/Sm3+ co-doped BaSrAlBS glasses exhibit a mixture of emission exhibited by individual ions when excited at 368 nm, whereas it exhibits only red-orange light emission when excited under 402 nm. The PL lifetimes demonstrated a reduction in decay time as Sm3+ ions concentration increased in Tb3+ doped BaSrAlBSi glasses. CIE coordinates show the green emission was tuned towards the warm white region via co-doping of Sm3+ in Tb3+ doped BaSrAlBSi glasses. The strong thermal stability of BSi:TbSm1.0 glass is confirmed via a temperature-dependent emission profile. The observed results indicate that the transparent BSi:TbSm1.0 glasses as made will be directly useful for photonic device applications as n-UV pumping results in green warm white and orange emissions.

Tuneable luminescence of Pr3+-doped sodium aluminium gadolinium phosphate glasses for photonics applications

Pr3+ doped sodium aluminium gadolinium phosphate (Pr:NaAlGdP) glasses were prepared to characterize on the structure, physical and especially spectroscopic properties. From XRD and FTIR results, synthesized glasses had the amorphous nature with phosphate complexes as the main structure units. The density, molar volume and refractive index of glass increased with increment of Pr2O3 concentration. The absorption spectra demonstrated the strong absorbance of Pr3+ dopant in visible light and near infrared region. The emission spectra recorded under 444, 468 and 481 nm excitation exhibited overlapping of Pr3+ emission from two emitting levels, 1D2 and 3P0. The 1D2→3H4 transition was of the highest intensity with emission maxima at 600 nm. The distinct excitation wavelengths caused the different emission patterns, resulting to the tuneable color of emission as pink, orange, and reddish orange. The optimum concentration of Pr2O3 in NaAlGdP glass is 0.1 mol% with the highest photoluminescence intensity and the 2nd longest decay time in hundred microsecond order. The non-single exponential decay profile and the reduction of decay time with added Pr2O3 content indicated the resonant energy transfer between Pr3+ ions. The high values of stimulated emission cross-section, branching ratio and quantum efficiency from Judd-Ofelt analysis confirmed the potential lasing action and light emitting with 600 nm from this glass. The radioluminescence study also represented the interesting ability of glass for X-ray detection. The Pr:NaAlGdP glass is a promising new photonics material for the tuneable light source, LED, display / screen, waveguide and laser medium.

Investigation of the relation between photoluminescence intensity and decay time reduction with plasmon effect in InGaAs quantum dots

Plasmonic effects on photoluminescence are investigated via time-integrated and resolved photoluminescence (PL) in epitaxially grown InGaAs quantum dots (QDs). The decay time and PL intensities are compared as a function of the density of Ag nanoplates. Optimal conditions for both reduction lifetime and enhanced PL intensity were found to be a 1:15 ratio of Ag nanoplates to water. Both less and greater than that ratio 1:15, the lifetime increased and the enhancement factor of PL intensity decreased. In addition, the plasmon effect was investigated via resonance wavelength and temperature-dependent PL measurements. At 150K near the resonance conditions between PL from InGaAs QDs and Ag nanoplates, both the lifetime reduction and enhancement factor are maximized. Intensity enhancement is correlated to lifetime reduction for various conditions to identify a condition for maximized enhancement of radiative recombination for designing future ultrafast plasmonic nanolasers.

Deterministic coupling of a system of multiple quantum dots to a single photonic cavity mode

We fabricated and studied a system comprising four site-controlled semiconductor quantum dots (QDs) embedded in a linear photonic crystal membrane cavity. The excellent position control and small spectral broadening permit coupling of the emission of all four QDs to the same photonic cavity modes. This is corroborated by co-polarization of the QD and cavity emission lines, as well as reduction in decay time, both with characteristic dependence on QD-cavity energy detuning. Scaling up to larger QD systems is discussed.

Nonlinear absorption and excited state dynamics of porphyrin and phthalocyanine in the presence of explosive molecules

Nonlinear absorption (NLA) properties and excited state dynamics of a porphyrin and phthalocyanine in the presence of explosive molecules were investigated using the nanosecond Z-scan and femtosecond pump-probe techniques, respectively. The NLA coefficients Is and β increased in the presence of explosive molecules. The change in first excited state decay time was evaluated through degenerate pump-probe measurements near 700nm and it was observed that decay time decreased in the presence of explosive molecules. The reduction in decay time and increase in NLA coefficients varied with different molecules according to their absorption, emission properties and affinity towards the explosive molecule.

Plasmonic enhancement in upconversion emission of La2O3:Er3+/Yb3+ phosphor via introducing silver metal nanoparticles

In the present work, authors have synthesized silver (Ag) nanoparticle (NP) embedded La2O3:Er3+/Yb3+ powder phosphor. The synthesis method has resulted in silver oxide–lanthanum oxide composite material. Through subsequent heat treatment of sample in pellet form, the silver metal nanoparticles were formed. The presence of plasmonic Ag NPs in the matrix is confirmed by various techniques. Large enhancement in downconversion as well as upconversion emission intensity of Er3+ ions at various concentrations of Ag NPs is obtained. Large enhancement in the upconversion emission intensity is correlated to the reduction in decay time of 4S3/2 level in the presence of Ag NPs, and possible reasons for intensity enhancement are discussed. The application of phosphor in fingermark detection is demonstrated.

Enhanced temperature sensing response of upconversion luminescence in ZnO–CaTiO3: Er3+/Yb3+ nano-composite phosphor

Upconversion emission and temperature sensing of the Er3+/Yb3+ doped ZnO–CaTiO3 nano-composite phosphor is studied by varying the ZnO concentration. The XRD and EDX studies reveal the formation of composite phase when ZnO doping exceeds above 10 mw%. Five prominent upconversion emission bands at 410, 492, 524, 545 and 662nm corresponding to 2H9/2→4I15/2, 4F3/2→4I15/2, 2H11/2→4I15/2, 4S3/2→4I15/2 and 4F9/2→4I15/2 transitions, respectively are found under 980nm excitation from a diode laser. On the basis of rise time analysis it was found that energy transfer process is responsible for the intense upconversion emission. Large reduction in decay time of 4S3/2 level is observed on the ZnO incorporation in host matrix. Moreover, the absolute sensor sensitivity, relative sensor sensitivity and calculated color coordinates of the samples are also determined. These results indicate the potentiality of this composite phosphor for various applications.

On the validity of the ambipolar diffusion assumption in the polar mesopause region

Abstract. The decay of underdense meteor trails in the polar mesopause region is thought to be predominantly due to ambipolar diffusion, a process governed by the ambient temperature and pressure. Hence, observations of meteor decay times have been used to indirectly measure the temperature of the mesopause region. Using meteor observations from a SKiYMET radar in northern Sweden during 2005, this study found that weaker meteor trails have shorter decay times (on average) than relatively stronger trails. This suggests that processes other than ambipolar diffusion can play a significant role in trail diffusion. One particular mechanism, namely electron-ion recombination, is explored. This process is dependent on the initial electron density within the meteor trail, and can lead to a disproportionate reduction in decay time, depending on the strength of the meteor.

Fabrication of CdSe–ZnS nanocrystal-based local fluorescent aperture probes by active polymerization of photosensitive epoxy

We report the fabrication of a nanocrystal (NC) doped polymer tip at the end of a single-mode optical fiber with active polymerization technique. The tip is created by immersing the fiber in a photosensitive epoxy precursor containing colloidal CdSe–ZnS NCs and polymerizing the epoxy using laser light introduced through the fiber. The laser power was found to have a strong influence on the tip height and shape. As the laser beam progressed from the fiber end, the power was reduced by conversion and absorption, resulting in a cone-shaped tip. The shape of the extreme end of the tip was sensitive to the transmitted beam pattern, indicating that the shape of the tip is independent of the substrate fiber. A blue shift and reduction in decay time suggest that the emission properties of the NCs are affected by immobilization in the epoxy, possibly because of oxidation at the NC surface.

A new biasing technique for transition edge sensors with electrothermal feedback

We have developed a new operating mode for superconducting transition edge sensors (TES) used in cryogenic particle detection which use electrothermal feedback (ETF). By using the new technique with the optical photon detectors our group has developed, we have been able to reduce the decay time of the pulses from the detector by more than a factor of five. The technique involves reducing the voltage bias across the tungsten superconducting detector during a pulse. By reducing the voltage during a pulse, there is an additional reduction in joule heating which speeds up the recovery of the detector. In theory, the technique reduces the decay time of the pulses which allows for higher maximum count rates. In addition to a brief theoretical analysis of the benefits of the technique, we present experimental results and analysis demonstrating a pulse decay time reduction by a factor of five.

Changes in cochlear mechanics during vocalization: evidence for a phasic medial efferent effect

The mustached bat, Pteronotus p. parnellii, has a finely tuned cochlea that rings at its resonant frequency in response to an acoustic tone pip. The decay time (DT) and frequency of these damped oscillations can be measured from the cochlear microphonic potential (CM) to study changes in cochlear mechanics. In this report, we describe phasic changes that occur in synchrony with communication sound vocalizations of the bat. Three animals with chronically implanted electrodes were studied. During the experiments, 1–2 ms tone pips were emitted from a speaker every 200 ms. This triggered a computer analysis of the resulting CM to determine the DT and cochlear resonance frequency (CRF) of the ringing. The time relative to vocalizations was determined by monitoring the output of a microphone placed near a bat's mouth. Similar results were obtained from all three bats tested. In a representative case, the average DT was 2.33±0.25 ms while the bat was quiet, but it decreased by 46% to 1.26±0.75 during vocalizations, which indicates a greater damping of the cochlear partition. Sometimes, DT started decreasing immediately before the bat vocalized. After the end of a vocalization, the return to baseline values varied from rapid (milliseconds) to gradual (1–2 seconds). The CRF also changed from baseline values during vocalization, although the amount and direction of change were not predictable. When gentamicin was administered to block the action of medial olivocochlear (MOC) efferents, DT reduction was still evident during vocalization but less pronounced. We conclude that phasic changes in damping occur in synchrony with vocalization, and that the MOC system plays a role in causing suppression. Since suppression can begin prior to vocalization, this may be a synkinetic effect, mediated by neural outflow to the ear in synchrony with neural outflow to the middle ear muscles and the muscles used for vocalization.

TORSIONAL VIBRATION CONTROL OF A FLEXIBLE BEAM USING LAMINATED PVDF ACTUATORS

This paper describes a theoretical and experimental development of a laminated spatially distributed piezoelectric torsional vibration actuator for a clamped-free cantilever beam. The strain energy transferred from a piezoelectric film actuator to a substructure is derived as a function of actuator strain only and is then used to calculate the induced strain in a substructure loaded in uniaxial extension/compression, bending and torsion. This transferred energy can be maximized by optimizing the actuator/structure dimensions and material properties. An experimental cantilever beam was constructed to examine the first mode decay in torsion under the influence of the actuators. The theoretical and experimental decay histories of the first torsion mode decay indicate a reduction in decay time for the controlled beam of greater than 10 times that of the uncontrolled beam.

Thermal behaviour of low temperature coherent emission in LiYF4:Er3+

In single crystal of LiYF4:Er3+ with two unparallel unpolished faces, coherent emission at 2.72 μm is observed at low temperature from 9 K to 60 K when excited by cw krypton ion laser line at 6471 Å. Several experimental fact such as square law behaviour, spectral narrowing, reduction of decay time, show that superfluorescence occurs under continuous excitation at low threshold.