Wavelength selectors using

Instrumentation capable of acquiring data in a multidimensional format using parallel detectors is similar to that of conventional spectrofluorimeters. The major differences are the type of detector, light source, and wavelength selectors used. In a conventional fluorimeter, a photomultiplier tube is used as... 

A wavelength selector that uses either absorption, or constructive and destructive interference to control the range of selected wavelengths. 

A wavelength selector that uses a diffraction grating or prism, and that allows for a continuous variation of the nominal wavelength. 

If the researcher has commercial molecular luminescence instrumentation (e.g., a spectrofluorometer) available, then solid-state luminescence data should not be difficult to obtain. Many good references are available discussing the basic theory of luminescence, " so the focus herein will be on its use in solid-state applications. Instrumentation normally consists of an excitation source, excitation wavelength selector, sample compartment, emission wavelength selector, and detector. The largest issue for conducting measurements on... 

The basic components of spectrophotometers are a light source, wavelength selector, absorption cell (cuvette), and photodetector. Colorimeters or absorptiometers commonly use nondispersive wavelength selection (a filter with bandwidth 4 -40 nm) and solid state or simple phototube detectors, while spectrophotometers employ a prism or grating monochromator (with bandwidth down to 0.2 nm) and a photomultiplier. Colorimeters are inexpensive and most appropriate for repetitive measurements of absorption at a fixed wavelength. The more expensive spectrophotometer can also fulfill this function, but its main purpose, by virtue of its accurate and variable wavelength control, is the measurement of absorption spectra. 

Wavelength selector A device that limits the range of wavelengths used for an optical measurement. 

A monochromator is usually used as a wavelength selector. Monochromators are composed of a dispersing medium to separate the wavelengths of the polychromatic radiation from the source, slits to select the narrow band of wavelengths of interest and lenses or mirrors to focus the chosen radiation. 

A system of slits (Fig. 2.17) is used to select radiation from the light beam both before and after it has been dispersed by the wavelength selector. The jaws of the slit are made of metal and are usually shaped like two knife edges. They can be moved relative to each other to change the mechanical width of the sht as desired. For the sake of simplicity, Fig. 2.17 does not show the system of lenses or mirrors used in a monochromator to focus and colhmate the light as needed. 

A schematic block diagram of the instrumentation used for AAS is shown in Fig. 6.3. The components are similar to those used in other spectroscopic absorption methods as discussed in Chapters 2 and 5. Light from a suitable source is directed through the atomizer, which serves as the sample cell, into a wavelength selector and then to a detector. The detector measures how much light is absorbed by the sample. The sample, usually in solution... 

Two wavelength selectors are used in flame OES, monochromators and filters. 

These work at predefined wavelengths, they have no moving parts. Because LEDs emit radiation of discrete wavelengths, these instruments do not need any wavelength selector (filter, monochromator etc.). Additional interference filters can be used in order to limit the spectral bandwidth. Advantages are the possibihty of miniaturisation and the high stability of these light sources. 

The excitation wavelength selector can be either a filter or a monochromator. Filters offer better detection Hmits, but do not provide spectral scanning capabilities. Often, a filter is used in the excitation beam along with a monochromator in the emission beam to allow emission spectra to be acquired. FuU emission and excitation spectral information can be acquired only if monochromators are used in both the excitation and emission beams. In modern instruments with array detectors, a polychromator is used in the emission beam instead of a monochromator. Recent research instraments are able to scan both wavelengths automatically and combine all data into a 2D excitation—emission spectrum. In lifetime spectrometers, a pulsed light source and a gated detector are synchronized in order to measure the time dependence of the luminescence emission. 

In FES, grating or quartz-prism monochromators are commonly used as wavelength selectors for the polychromatic line radiation coming from the atom reservoir (flame). 

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