Luminescence instrumentation monochromators

The basic components of luminescence instrumentation are generally arranged as shown in Fig. 1. The sample is placed in a sample cell and excited by either ultraviolet or visible light from a source. A filter or monochromator may select a particular excitation... 

When a luminescence spectrum is obtained on an instrument such as that used to produce the spectra in Figure 7.23, it will depend on the characteristics of the emission monochromator and the detector. The transmission of the monochromator and the quantum efficiency of the detector are both wavelength dependent and these would yield only an instrumental spectrum. Correction is made by reference to some absolute spectra. Comparison of the absolute and instrumental spectra then yields the correction function which is stored in a computer memory and can be used to multiply automatically new instrumental spectra to obtain the corrected spectra. The calibration must of course be repeated if the monochromator or the detector is changed. 

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. 

Hgure 4 Schematic diagram of instrumental components for the measurement of SPF. S, source Ml, excitation monochromator SP, solid phase with sample M2, emission monochromator D, detector. (Adapted with permission from Robert JH (1995) Luminescence Solid Phase, pp. 2749-2756 Elsevier.)... 

The Perkin Elmer LS-3B instrument is a fluorescence spectrometer with separate scarming monochromes for excitation and emission, and digital displays of both monochromator wavelengths and signal intensity. The LS-5B instrument is a rotating luminescence spectrometer with the capability of measuring fluorescence, phosphorescence, and bio-and chemiluminescence. Delay time (t ) and gate width (tj are variable via the keyboard in 10 ps intervals. The instrument collects excitation and emission spectra. 

The principle of a sophisticated array-detector-based instrument to produce total luminescence spectra is illustrated in Figure 1.5-12a. Here, the length of a sample cell is irradiated with an excitation beam that has been dispersed along the. ry plane by a monochromator that has been rotated 90 with respect to its exit slit. The transducer is a two-dimensional charge-... 

In luminescence spectroscopy the emission of the luminophore is monitored. There are two different types of luminescence spectra that can be recorded with modern spectrofluorometers, emission and excitation spectra. Note that although the name implies that these instruments measure only fluorescence, spectrofluorometers can also measure phosphorescence, especially when special accessories are added. Spectrofluorometers contain both an excitation monochromator and an emission monochromator. In emission spectra, the excitation wavelength is fixed and the emission monochromator is scanned. The excitation is usually fixed at a wavelength at which the sample has significant absorbance. In excitation spectra, on the other hand, the emission wavelength is fixed and the excitation monochromator is scanned. The emission is normally fixed at a... 

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