In this work, we have designed, fabricated and characterized silicon nitride sub-wavelength gratings on glass substrate to enhance the fluorescence in the green-red wavelength range. Silicon nitride was chosen as the material to fabricate the gratings as it exhibits low absorption losses and negligible fluorescence at visible wavelengths. Due to lower refractive index contrast, the structures were designed such that the medium index contrast gratings still achieve good quality factor resonances by using higher duty cycles (~ 70%) which clearly distinguishes two-mode region from higher order diffraction regime. The designed structure (Duty cycle: ~70%, thickness: 290nm, pitch: 370nm) supports resonant modes at 542nm for TE and at 548nm and 568nm for TM polarization. Rhodamine B dye was attached to the grating through an intermediate polymer layer PAH (Polyallylamine hydrochloride) by dip coating method. Using a fluorescence microscope with suitable excitation (510-550nm) and emission (>590nm) filters, we observed fluorescence enhancement of 5.4x and 5.8x in TE and TM modes respectively.
The quest for the development of portable thermophotovoltaic (TPV) systems has been a growing interest due to the ability to achieve high power and energy densities using hydrocarbon based fuels. Recent studies based on intermediate filters and photonic crystals have shown significant improvement in system efficiencies for combustion driven and solar-based TPV systems. The key goal is to engineer directionally and spectrally selective thermal emitters ideally matched to the solar cell. Here, a high contrast grating based thermal emitter using silicon as a grating material on a quartz substrate is proposed which is suitable for integrating to GaSb solar cell based thermophotovoltaic systems powered by microcombustor. The intrinsic properties of quartz substrate filter the below bandgap (greater than 4.5 μm) radiation in the infrared region. The silicon gratings are optimized (period = 2.4 μm, duty cycle = 40 % and thickness = 0.55 μm), to provide transmission only for photons with wavelengths lower than 1.8 μm thus inhibiting below bandgap radiation of GaSb cell. The spectrally tuned emitter structure shows transmission of more than 70% of convertible photons (above the bandgap) and reflection of 80% of unconvertible photons (below bandgap) back to the combustor thus reducing the heat losses in the photovoltaic conversion and increasing the combustion system temperature there by contributing to overall increase in TPV system efficiency.
Water quality monitoring has become important in today’s scenario due to severe chemical and bacterial contamination in urban and rural water bodies. However, current monitoring methods do not provide fast and reliable results. By using intrinsic fluorescence, microbial contamination and industrial pollutants in water can be monitored in real-time, continuously and at very low concentrations. Intrinsic fluorescence can be enhanced by using High Contrast Gratings (HCGs) spectrally tuned to the fluorescence signatures of pollutants. Compared to metallic gratings which suffer from higher losses especially at lower wavelengths and are easily prone to oxidation, an all dielectric approach can overcome these limitations. HCGs using silicon nitride as grating material on a glass substrate are optimized to detect the presence of tryptophan (a bio-chemical marker for bacterial contamination) and phenanthrene (chemical contaminant). Tryptophan and phenanthrene have a fluorescence emission wavelength of 410 nm and 420 nm respectively. HCGs are optimized to enhance fluorescence emission at both of these wavelengths, therefore the optimized grating parameters for tryptophan (period: 255 nm, duty cycle: 0.8 and thickness: 260 nm) and phenanthrene (period: 282 nm, duty cycle: 0.8 and thickness: 289 nm) resulted in Q factor of 683 and 709 respectively. The optimized HCGs show an electric field enhancement of eight times concentrated in the air region between the gratings which would result in enhanced fluorescence.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.