Enhanced frequency upconversion of Sm3+ ions by elliptical Au nanoparticles in dichroic Sm3+: Au-antimony glass nanocomposites

Dichroic Sm³⁺: Au-antimony glass nanocomposites are synthesized in a new reducing glass (dielectric) matrix (mol%) K₂O–B₂O₃–Sb₂O₃ (KBS) by a single-step melt-quench technique involving selective thermochemical reduction. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results indicate that Au⁰ nanoparticles are grown along the (2 0 0) plane direction. The transmission electron microscopic (TEM) image reveals the elliptical Au⁰ nanoparticles having major axis range 12–17 nm. Dichroic behavior is due to elliptical shape of Au⁰ nanoparticles of aspect ratio ～1.2. Au⁰ NPs of concentration of 0.03 wt% (4.1 × 10¹⁸ atoms/cm³) drastically enhances the intensity (～7-folds) of electric dipole ⁴G_5/2 → ⁶H_9/2 red transition (636 nm) of Sm³⁺ ions and then attenuates with further increase in Au⁰ concentration. The magnetic dipole ⁴G_5/2 → ⁶H_5/2 green (566 nm) and ⁴G_5/2 → ⁶H_7/2 orange (602 nm) transitions remain almost unaffected by presence of nano Au⁰. Local field enhancement (LFE) induced by Au⁰ SPR and energy transfer (ET) from fluorescent Au⁰ → Sm³⁺ ions are found to be responsible for the enhancement while reverse ET from Sm³⁺ → Au⁰ and optical re-absorption due to Au⁰ SPR for attenuation.     

Effects of nano-YAG (Y3Al5O12) crystallization on the structure and photoluminescence properties of Nd3+-doped K2O–SiO2–Y2O3–Al2O3 glasses

Nd³⁺-doped precursor glass in the K₂O–SiO₂–Y₂O₃–Al₂O₃ (KSYA) system was prepared by the melt-quench technique. The transparent Y₃Al₅O₁₂ (YAG) glass–ceramics were derived from this glass by a controlled crystallization process at 750 °C for 5–100 h. The formation of YAG crystal phase, size and morphology with progress of heat-treatment was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transformed infrared reflectance spectroscopy (FT-IRRS). The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range 25–40 nm. The measured photoluminescence spectra have exhibited emission transitions of ⁴F_3/2 → ⁴I_J (J = 9/2, 11/2 and 13/2) from Nd³⁺ ions upon excitation at 829 nm. It is observed that the photoluminescence intensity and excited state lifetime of Nd³⁺ ions decrease with increase in heat-treatment time. The present study indicates that the incorporation of Nd³⁺ ions into YAG crystal lattice enhance the fluorescence performance of the glass–ceramic nanocomposites.     

Physical process first law and increase of horizon entropy for black holes in Einstein-Gauss-Bonnet gravity

We establish the physical process version of the first law by studying small perturbations of a stationary black hole with a regular bifurcation surface in Einstein-Gauss-Bonnet gravity. Our result shows that when the stationary black hole is perturbed by a matter stress energy tensor and finally settles down to a new stationary state, the Wald entropy increases as long as the matter satisfies the null energy condition.     

Radiation-pressure acceleration of ion beams from nanofoil targets: the leaky light-sail regime

A new ion radiation-pressure acceleration regime, the "leaky light sail," is proposed which uses sub-skin-depth nanometer foils irradiated by circularly polarized laser pulses. In the regime, the foil is partially transparent, continuously leaking electrons out along with the transmitted laser field. This feature can be exploited by a multispecies nanofoil configuration to stabilize the acceleration of the light ion component, supplementing the latter with an excess of electrons leaked from those associated with the heavy ions to avoid Coulomb explosion. It is shown by 2D particle-in-cell simulations that a monoenergetic proton beam with energy 18 MeV is produced by circularly polarized lasers at intensities of just 101? W/cm2. 100 MeV proton beams are obtained by increasing the intensities to 2 × 102? W/cm2.     

Kinetics and mechanism of the ligand substitution reaction of di-μ-hydroxobis(bipyridyl)dipalladium(II) ion with thiourea in aqueous solution

The kinetics of the interaction between thiourea and the title complex has been studied spectrophotometrically in aqueous medium as a function of nucleophile concentration, temperature and pH at constant ionic strength. The reaction is a two-step process in which the first step is ligand dependent, but the second step is ligand independent and is assigned to ring closure. The rate and activation parameters, conductivity studies and IR data were used to deduce a plausible mechanism.     

NOVEL CHEBYSHEV DISTRIBUTED CHIRPED PHOTONIC BANDGAP (PBG) STRUCTURES

A microstrip transmission line on a Chebyshev distributed chirped I-D photonic bandgap structure (PBGS) is proposed. Two different approaches are utilized to realize Chirped PBGS. Firstly, the inter-element distance of PBG elements is chirped with conventional chirping technique. Secondly, using Chebyshev distribution varies the inter-element distance. For both the cases, the amplitude is made non-uniform by varying the amplitudes in accordance with the co-efficient of Chebyshev distribution. It can be seen that the conventionally chirped PBGS having Chebyshev distribution in amplitude improves the over all performance. The inclusion of Chebyshev distribution in period calculation further improves the performance. It can be seen that the Chirped and non-uniform PBGS generates excellent bandgap performances in lower valued height of substrate that are superior to the performances available in the open literature.     

Experimental lifetimes of some levels belonging to the 4p5d configuration of KrII

Lifetime of eight levels belonging to the 4p⁴5d configuration of singly ionized krypton have been measured by high-frequency deflection technique with a delayed coincidence single photon counting arrangement. The results have been compared with other experimental and theoretical values. The lifetimes of the 5d⁴P_1/2, 5d^′2D_3/2, 5d^′2F_5/2, 5d²P_3/2 and 5d²P_1/2 levels have been measured for the first time.