Spectral emission bands

Certain compounds, when excited in solution by visible or near ultraviolet radiation, re-emit all or part of this energy as radiation. According to Stokes law, the maximum of the spectral emission band is located at a higher wavelength than that of either the incident radiation or the excitation band maximum (see Figs I2.l and 12.2). After excitation, the intensity of the emitted light decreases (decays) exponentially according to equation (l2.l), which relates the instantaneous intensity to time ... 

Minimizing Spectral Interferences The most important spectral interference is a continuous source of background emission from the flame or plasma and emission bands from molecular species. This background emission is particularly severe for flames in which the temperature is insufficient to break down refractory compounds, such as oxides and hydroxides. Background corrections for flame emission are made by scanning over the emission line and drawing a baseline (Figure 10.51). Because the temperature of a plasma is... 

GaP N, is clearly evident. The addition of N shifts the peak to longer wavelengths and broadens the spectral emission. The curves for the AIGalnP LEDs represent devices of three different alloy compositions, all exhibiting recombination for the conduction band direct minimum. The emission spectmm of the blue InGaN LED exhibits uniquely broad emission, most likely as a result of recombination via deep Zn impurities levels (23). 

Combined Soot W2O, and CO2 Radiation The spectral overlap of H9O and CO9 radiation has been taken into account by the constants for obtaining Ec- Additional overlap occurs when soot emissivity , is added. If the emission bands of water vapor and CO9 were randomly placed in the spectrum and soot radiation were gray, the combined emissivity would be Eg phis , minus an overlap correction g s- But monochromatic soot emissivity is higher the shorter the wavelength, and in a highly sooted flame at 1500 K half the soot emission hes below 2.5 [Lm where H9O and CO9 emission is negligible. Then the correction g s must be reduced, and the following is recommended ... 

Photoexcitation of Cu rare-gas films in the region of the 2P 2S absorption band produces intense narrow emissions bands showing large spectral red shifts as seen in Figure 4,(34). 

One important factor which limits the performance of flame AAS is interference, both spectral and chemical. Spectral interference occurs where emission lines from two elements in the sample overlap. Despite the huge number of possible emission lines in typical multielement samples, it is rarely a problem in AA, unless molecular species (with broad emission bands) are present in the flame (in which case, a higher temperature might decompose the interfering molecule). If spectral interference does occur (e.g., A1 at 308.215 nm, V at 308.211 nm) it is easily avoided by selecting a second (but perhaps less sensitive) line for each element. 

Spectral lines for atoms are absorption or emission bands that are so narrow that they appear as lines rather than bands. 

This comparison of the spectroscopic properties of the different types of fluorescent reporters underlines that semiconductor QDs and upconverting nanoparticles have no analogs in the field of organic dyes. Therefore, their unique features are unrivaled. The different molecular labels detailed here each display unique advantages that can compete with some of the favorable features of QDs and upconverting phosphors such as long lifetimes in the case of MLC systems and lanthanide chelates or very narrow emission bands for lanthanide chelates beneficial for spectral multiplexing. 

The chromophore environment can affect the spectral position of the absorption and emission bands, the absorption and emission intensity (eM, r), and the fluorescence lifetime as well as the emission anisotropy, e.g., in the case of rigid matrices or hydrogen bonding. Changes in temperature typically result only in small spectral shifts, yet in considerable changes in the fluorescence quantum yield and lifetime. This sensitivity can be favorably exploited for the design of fluorescent sensors and probes [24, 51], though it can unfortunately also hamper quantification from simple measurements of fluorescence intensity [116], The latter can be, e.g., circumvented by ratiometric measurements [24, 115],... 

Spectral multiplexing or multicolor detection is typically performed at a single excitation wavelength, and relies on the discrimination between different fluorescent labels by their emission wavelength. Desirable optical properties of suitable fluoro-phores are a tunable Stokes shift and very narrow, preferably well-separated emission bands of simple shape. 

The complexation with CDs also results in spectral shifts of the absorption and emission maxima of cyanine dyes. The complexation of cyanine dyes 1 (X = S, R = Et, n = 1-3) with p-CD red-shifts the emission bands [25]. 

On the one hand, the output wavelength of a dye laser can be continuously varied within their broad emission band (various tens of nanometers). Therefore, with different dyes the overall spectral range covered by these lasers can be extended from around 400 nm to 1.1 jim, as shown in Figure 2.12. 

The optical features of a center depend on the type of dopant, as well as on the lattice in which it is incorporated. For instance, Cr + ions in AI2O3 crystals (the ruby laser) lead to sharp emission lines at 694.3 nm and 692.8 nm. However, the incorporation of the same ions into BeAl204 (the alexandrite laser) produces a broad emission band centered around 700 nm, which is used to generate tunable laser radiation in a broad red-infrared spectral range. 

The IR detector utilizes a combination of three IR sensors of extremely narrow band response. One covers the typical CO2 emission spectral band, and the two other sensors cover different adjacent specially selected spectral bands. While the CO2 emission band sensor is responsible for the detection of... 

Previous experience in arc and spark emission spectroscopy has revealed numerous spectral overlap problems. Wavelength tables exist that tabulate spectral emission lines and relative intensities for the purpose of facilitating wavelength selection. Although the spectral interference information available from arc and spark spectroscopy is extremely useful, the information is not sufficient to avoid all ICP spectral interferences. ICP spectra differ from arc and spark emission spectra because the line intensities are not directly comparable. As of yet, there is no atlas of ICP emission line intensity data, that would facilitate line selection based upon element concentrations, intensity ratios and spectral band pass. This is indeed unfortunate because the ICP instrumentation is now capable of precise and easily duplicated intensity measurements. 

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