High-quality Emission Research Articles

Environment friendly Co/Ag@ZnS quantum dots with high quality emission and application for selective sensing of Hg2+

Mercury (Hg), being a highly toxic environmental contaminant, poses serious ecological and health problems even at low quantities. Accurate and sensitive methods for detecting Hg2+ ions in environment are desperately needed. Also, the production of red emissive nanophosphors with outstanding color purity is a critical requirement for the next-generation display systems and lighting industry. A red emitting Co/Ag@ZnS QDs phosphor were prepared and studied to enhance the color characteristics of warm white light emitting diodes. The phosphors are synthesized using a co-precipitation technique, and the evolution of emission spectra are examined by the addition of dopants, significantly increasing PL QY up to 27.6%. A highly sensitive fluorescence sensor has been fabricated for Hg2+ detection using a quenching mechanism that has an excellent linear range of 0–50 µM, a correlation coefficient of 0.989, and a detection limit of 0.13 µM. More crucially, the proposed fluorescence sensing platform successfully and satisfactory detects Hg2+ in real water samples. These phosphors, which exhibit impressive CIE chromaticity coordinates, good CCT values, and high color purity (91.1%) may find substantial use in displays and demonstrate their effectiveness as red phosphors.

An Apparatus for Spectral Emissivity Measurements of Thermal Control Materials at Low Temperatures.

Thermal control materials are employed to adjust the temperature of a spacecraft operating in deep space. The spectral emissivity is a crucial factor in evaluating the thermal radiative properties of such materials. An apparatus, composed of a Fourier transform infrared spectrometer (FTIR), a sample cooling chamber and a mechanical modulation system was demonstrated to measure low temperature infrared spectral emissivity under vacuum. The mechanical modulation system, which includes a chopper and a lock-in amplifier, is employed to reduce the interference of background radiation during measurements. The limitation of the Fourier transform frequency on the chopper frequency can be eliminated by setting the FTIR on step-scan mode. The apparatus is separated into two parts and evacuated by different pumps. In this study, a high quality emission spectrum of a sample is measured by the apparatus. The spectral emissivity of thermal control materials are obtained in the wavelength range of 8 to 14 μm at 173 and 213 K. The combined standard uncertainty of the apparatus is 3.30% at 213 K.

Open cut black coal mining: Empirical verification of PM2.5 air emission estimation techniques

There is a paucity of empirical data relating to PM2.5 emissions from open cut coal mines. Availability of high quality emission data is fundamental to the completion of robust analyses of the potential future impacts of particulate emissions from open cut coal mining operations. This study presents PM2.5 emission rates determined on the basis of empirical data from open cut coal mining operations located in two regions of Australia. These data are used to validate the currently adopted PM2.5 emission estimation methodologies, which are based on total suspended particulate measurements adjusted for PM2.5 size fraction. The emission rates determined in this study demonstrate that regional differences between emission rates may be significant for specific activities. Measured average PM2.5 emission rates are compared to rates calculated using existing available emissions estimation methodologies. This reveals that for dragline operation and coal dumping there are significant differences between the measured emission rates and emission rates calculated using currently available methodologies. This study identifies that the existing adopted US EPA and Australian emissions estimation methods for PM2.5 emissions from coal haul routes, which are one of the most significant sources of PM2.5 emissions at open cut mines, are reliable if the surface moisture content and dust control watering regimes are appropriately accounted for. The Australian estimation method is also considered reliable for overburden haul routes, however the US EPA method over predicts the measured PM2.5 emission rate by a factor of 3.Further, the study highlights that there is a high degree of inherent uncertainty in empirically derived emissions estimates for fugitive dust sources of this type. This uncertainty should be considered when completing emissions calculations, particular where these estimations are subsequently the basis for impact assessment and health risk analysis.

Substrate engineering for high-quality emission of free and localized excitons from atomic monolayers in hybrid architectures

Atomic monolayers represent a novel class of materials to study localized and free excitons in two dimensions and to engineer optoelectronic devices based on their significant optical response. Here, we investigate the role of the substrate on the photoluminescense response of MoSe$_2$ and WSe$_2$ monolayers exfoliated either on SiO$_2$ or epitaxially grown InGaP substrates. In the case of MoSe$_2$, we observe a significant qualitative modification of the emission spectrum, which is widely dominated by the trion resonance on InGaP substrates. However, the effects of inhomogeneous broadening of the emission features are strongly reduced. Even more strikingly, in sheets of WSe$_2$, we could routinely observe emission lines from localized excitons with linewidths down to the resolution limit of 70\,$\mu$ eV. This is in stark contrast to reference samples featuring WSe$_2$ monolayers on SiO$_2$ surfaces, where the emission spectra from localized defects are widely dominated by spectral diffusion and blinking behaviour. Our experiment outlines the enormous potential of III-V-monolayer hybrid architectures to obtain high quality emission signals from atomic monolayers, which are straight forward to integrate into nanophotonic and integrated optoelectronic devices.

Low Light CMOS Contact Imager with Integrated Dual Band Emission Filters for Fluorescence Detection

In recent times, the scope of optical imaging systems has been widened substantially to address the need for inexpensive, portable and miniaturized sensory system for applications such as in situ biomedical and environmental monitoring. Contact imaging is a relatively new and low-cost technique that offers significant advantages over conventional imaging. Conventional imaging systems often require bulky and expensive magnifying objectives along with photodetector devices. In contrast, contact imaging lacks the need of optical elements such as lenses between the sample and the sensor array, and therefore provides better light collection efficiency without optical loss and a significant improvement in sensitivity. Such unique features are achieved by contact imaging systems mainly due to direct coupling of the sensor array with the sample of interest via a thin-film filter.Fluorescence imaging is a powerful and highly sensitive tool that is widely used in diverse areas including diagnostic purposes, bioassays, pharmaceutical research and sensor development. Recently, contact image sensors fabricated using complementary metal-oxide semiconductor (CMOS) technology have been foreseen as an alternative to conventional fluorescence detection systems. Owing to the ability of CMOS imagers to integrate possibly all functions required for timing, exposure control, analog-to-digital (ADC) conversion, color processing, image enhancement and image compression on the same platform, they are considered key components of future micro-total-analysis-system (µTAS). CMOS imagers consume low power and require low voltage as well as facilitate a vast range of flexibility. However, fabrication of a high quality emission filter, also known as absorption filter, remains one of the major challenges in developing high sensitive CMOS-based fluorescence detection system. In particular, the integration of a CMOS image sensor with different types of filters that possess discrete cut-off wavelengths has so far been unexplored.Here, we demonstrate the fabrication of polyvinyl acetate (PVAc) based two distinct emission filters integrated with a single CMOS contact imager for fluorescence detection of two different analytes. PVAc was used as an adhesive for the emission filter due to its optical transparency, inexpensiveness and biocompatiblity properties. The fabrication process of emission filters involve dissolving PVAc in methanol, mixing it with absorbing specimens and finally drying up in air to harden the filter. Two distinct emission filters that possess discrete spectra are integrated onto a single CMOS image sensor. The integrated sensory system thus incorporates dual bandpass emission filters that are capable of selectively isolating fluorescence emission from two probes simultaneously. The thickness of the filters is optimized by calculating the desired signal-to-noise ratio (SNR) using Beer-Lambert’s law for liquids, Quantum Yield of the fluorophore and the Quantum Efficiency of the sensor array. Finally, the efficacy of the sensory system is tested by examining two different analytes i.e., calcium and pH. Overall, CMOS image sensor that combines dual bandpass emission filters holds much potential for low-cost and on-site deployable sensor development.

Assessing and controlling risks from the emission of organic chemicals from construction products into indoor environments

Construction products can be a significant source of indoor pollutants, including volatile organic compounds that may be a risk to the health and well-being of building occupants. There are currently a number of schemes for the labelling of products according to their potential to emit organic compounds. Assessment of the complex mixtures of compounds that may be released has mandated the development of test methods that allow the determination of the concentrations of the chemicals released from products in controlled test chamber environments. In response to concerns about the financial burden faced by manufacturers required to test products according to the various different labelling schemes currently in existence, the European Commission has investigated the scope for greater harmonisation. This initiative has sought to harmonise the process for the assessment of emissions data, complementing work led by the European standards organisation focussed on harmonising the test chamber procedures. The current labelling schemes have a range of requirements with respect to the number of chemicals to be quantified. A comparison of 13 schemes worldwide has identified 15 lists of target compounds, with a total of 611 chemicals occurring on at least one of the target lists. While harmonisation may clarify and perhaps simplify these requirements, at least in Europe, it can be expected that future changes to product formulations, the introduction of new products and our increasing knowledge about the potential risks to health, will require continued development of new and improved measurement techniques. There is, therefore, a particular challenge for analytical chemists to ensure the efficient provision of high quality emissions data and thereby ultimately enable effective control of risks to human health through the prevention or reduction of indoor air pollution.

66.4: Invited Paper: High‐Quality White OLEDs and Resource Saving Fabrication Processes for Lighting Application

AbstractWhite OLEDs with high efficiency (over 30 lm/W) and high quality emission characteristics (e.g., CRI of over 90, very small variation of chromaticity in different directions and chromaticity just on the black‐body radiation curve) applicable to “Lighting” were realized by a two‐unit structure with a fluorescent deep blue emissive unit and a phosphorescent green and red emissive unit. A new deposition source with a hot‐wall and a rate controllable valve was developed. Thickness uniformity within +/− 3% at high deposition rate of over 8 nm/s, high material utilization of over 70 %, and repeatable deposition rate controllability were confirmed.

Advanced experimental techniques for measuring oscillator strengths of vacuum ultraviolet lines

Advanced experimental techniques for measuring oscillator strengths of atomic and ionic transitions in the vacuum ultraviolet (VUV) are described. A VUV time-resolved laser-induced-fluorescence experiment for radiative lifetime measurements on atoms and ions in a beam is operational. Recent work on VUV transitions of Si I and B I is described. These lifetimes provide the essential absolute normalization for converting relative oscillator strengths to absolute transition probabilities. Emission measurements of branching fractions at VUV and longer wavelengths are proposed. A large echelle spectrograph equipped with a CCD detector array will be used. This experiment will provide the sensitivity, resolving power, and data handling capability required for extensive high quality emission branching fraction measurements. We further propose to use absorption measurements on hollow cathode discharges to determine relative absorption oscillator strengths. A demonstration of a new technique for absorption spectroscopy on glow discharges is reported. The new technique provides the sensitivity, dynamic range, and data handling capability required for extensive high quality absorption measurements. Relative absorption and emission oscillator strengths will be least-square adjusted using the bowtie method and normalized with accurate radiative lifetimes.

Spectroscopy of Cool Stars from IUE Data

After nine years of operation the IUE satellite continues to provide valuable spectra of cool stars from 1200 to 3100 Å. The impact of these spectra has been greatest in studies of the outer regions of the atmospheres, above the photospheres, allowing the general properties of stellar chromospheres, transition regions and winds to be established. After outlining these properties, I focus on studies based on high signal–to–noise echelle spectra (λ/Δλ ∼1.2 ×104) of single stars, showing how high quality emission line profiles have been used to derive constraints on the outer atmospheric structure, which in turn have been used to examine models of heating and mass loss.