7 research outputs found
Structural and optical studies of rare earth-free bismuth silicate glasses for white light generation
No full textWe report here rare-earth free bismuth silicate based oxyfluoride glasses (70-x) Bi2O3 30SiO(2) xMF (where M = Li, Na & K) with x = 5, 20 & 30 mol% that realizes white light. Bismuth silicate glasses are prepared by melt quenching method and characterized by Raman, Fourier transform infrared (FTIR), UV-VIS absorption and emission techniques. From the structural analysis, Raman and FTIR, we are able to find presence of BiO6 structural unit in the samples. Optical band gap values of present glass systems that are obtained from absorption spectra vary from 2.91 eV to 3.21 eV. Optical band gap values shows a correlation with theoretically calculated optical basicity values. Urbach energy calculated from absorption spectra gives a measure of disorder of present glass system. Quantitative description of Bi3+ ion interaction with silicate host lattice has been explored through Huang Rhys factor(S). The quality of white light emission is evaluated by CIE color matching function, color purity (CP) and correlated color temperature (CCT)
New candidate for red phosphor applications
No full textIn this paper red luminescence from BaBi(BO3)Ois reported and its origin is discussed with correlation to structure. Sample was prepared through solid state reaction method. X-ray diffraction were recorded to confirm the formation of BaBi(BO3)O. Diffused reflectance and Photoluminescence spectra were recorded to understand optical properties of the material. Raman spectroscopy were used to excavate the structural features of the material. Prepared sample exhibited luminescence in red region which will be useful towards white light emitting diode applications
Supercontinuum generation in antimony zinc borate glasses—A material perspective
No full textSupercontinuum (SC) generation from alkali antimony zinc borate glasses was investigated using a femtosecond laser. The optical bandgap values were determined for all the glass samples. An enhancement in the generated SC is seen from sodium-doped glass although it possesses the least bandgap among the glass samples. The physical parameters of the glasses such as density, molar volume, refractive index, oxide ion polarizability, and optical basicity have been analyzed and discussed. The smaller values of the metallization criterion indicate the tendency of the glass samples to exhibit metallic behavior, which, in turn, affects the non-linear optical properties of the glasses. The shift in the binding energies of metal cations and oxygen anions was observed using XPS analysis, which gives an understanding about the extent of overlapping of valence orbitals in the glass system. The observations from the physical and structural investigations provide an insight into the anomaly in the enhanced SC generation from the low bandgap sodium-doped glass
Photoluminescence & structural studies of Ag. Alkali bismuth silicate glasses
No full textIn this paper, we demonstrate the luminescence enhancement of Alkali Bismuth Silicate glasses through Silver incorporation. Silver has been incorporated into the glass matrix through three methods, namely by melt quench, ion implantation, and in-situ sputtering. Absorption spectra of the glasses show an inhomogeneously broadened surface plasmon resonance (SPR) peak along with the Bi2+ peak of Bismuth. The inclusion of Silver into the glass, by all three methods, enhances the photoluminescence and among them, in-situ sputtering gives better enhancement. Photoluminescence of the glasses is increasing with an increase in Ag-O intensity. Raman spectra is recorded to explore the role of glass structure in enhancement of luminescence viz., Silver oxide formation, Oxygen defect centers, etc,. The ion-implanted samples show Oxygen defect centers which deteriorate the luminescence intensity. CIE 1931 chromaticity colour coordinates (x,y) correlated colour temperature (CCT) and colour purity (CP) values were also determined from the photoluminescence data
Design and Numerical Simulation of Biomimetic Structures to Capture Particles in a Microchannel
No full textThe study of separating different sizes of particles through a microchannel has been an interest in recent years and the primary attention of this study is to isolate the particles to the specific outlets. The present work highly focuses on the design and numerical analysis of a microchip and the microparticles capture using special structures like corrugated dragonfly wing structure and cilia walls. The special biomimetic structured corrugated wing is taken from the cross-sectional area of the dragonfly wing and cilia structure is obtained from the epithelium terminal bronchioles to the larynx from the human body. Parametric studies were conducted on different sizes of microchip scaled and tested up in the range between 2–6 mm and the thickness was assigned as 80 µm in both dragonfly wing structure and cilia walls. The microflow channel is a low Reynolds number regime and with the help of the special structures, the flow inside the microchannel is pinched and a sinusoidal waveform pattern is observed. The pinched flow with sinusoidal waveform carries the particles downstream and induces the particles trapped in desired outlets. Fluid particle interaction (FPI) with a time-dependent solver in COMSOL Multiphysics was used to carry out the numerical study. Two particle sizes of 5 µm and 20 µm were applied, the inlet velocity of 0.52 m/s with an inflow angle of 50° was used throughout the study and it suggested that: the microchannel length of 3 mm with corrugated dragonfly wing structure had the maximum particle capture rate of 20 µm at the mainstream outlet. 80% capture rate for the microchannel length of 3 mm with corrugated dragonfly wing structure and 98% capture rate for the microchannel length of 2 mm with cilia wall structure were observed. Numerical simulation results showed that the cilia walled microchip is superior to the corrugated wing structure as the mainstream outlet can conduct most of the 20 µm particles. At the same time, the secondary outlet can laterally capture most of the 5 µm particles. This biomimetic microchip design is expected to be implemented using the PDMS MEMS process in the future
Temperature dependence of Coherent versus spontaneous Raman Scattering
No full textDue to their sub picosecond temporal resolution, coherent Raman
spectroscopies have been proposed as a viable extension of Spontaneous Raman
(SR) thermometry, to determine dynamics of mode specific vibrational energy
content during out of equilibrium molecular processes. Here we show that the
presence of multiple laser fields stimulating the vibrational coherences
introduces additional quantum pathways, resulting in destructive interference.
This ultimately reduces the thermal sensitivity of single spectral lines,
nullifying it for harmonic vibrations and temperature independent
polarizability. We demonstrate how harnessing anharmonic signatures such as
vibrational hot bands enables coherent Raman thermometry
Check-valve design in enhancing aerodynamic performance of flapping wings
No full textA flapping wing micro air vehicle (FWMAV) demands high lift and thrust generation for a desired payload. In view of this, the present work focuses on a novel way of enhancing the lift characteristics through integrating check-valves in the flapping wing membrane. Modal analysis and static analysis are performed to determine the natural frequency and deformation of the check-valve. Based on the inference, the check-valve opens and closes during the upstroke flapping and downstroke flapping, respectively. Wind tunnel experiments were conducted by considering the two cases of wing design, i.e., with and without a check-valve for various driving voltages, wind speeds and different inclined angles. A 20 cm-wingspan polyethylene terephthalate (PET) membrane wing with two check-valves, composed of central disc-cap with radius of 7.43 mm, supported by three S-beams, actuated by Evans mechanism to have 90° stroke angle, is considered for the 10 gf (gram force) FWMAV study. The aerodynamic performances, such as lift and net thrust for these two cases, are evaluated. The experimental result demonstrates that an average lift of 17 gf is generated for the case where check-valves are attached on the wing membrane to operate at 3.7 V input voltage, 30° inclined angle and 1.5 m/s wind speed. It is inferred that sufficient aerodynamic benefit with 68% of higher lift is attained for the wing membrane incorporated with check-valve.MOST補正完
