Luminescence instrumentation components

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... 

Commercial instruments can be used for solid-phase luminescence by simply using a solid-phase sample holder that is available from the manufacturer or by constructing a homemade sample holder. The instrumental components are described elsewhere in the encyclopedia. 

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.)... 

Several different schemes are used to correct luminescence spectra for some of the many variables that influence them. Source stability, source spectral distribution, inner filter effects, efficiencies of optical components, and spectral responses of instrument components are among the variables that can influence luminescence intensities and spectra. Many instru-... 

Luminescence lifetimes are measured by analyzing the rate of emission decay after pulsed excitation or by analyzing the phase shift and demodulation of emission from chromophores excited by an amplitude-modulated light source. Improvements in this type of instrumentation now allow luminescence lifetimes to be routinely measured accurately to nanosecond resolution, and there are increasing reports of picosecond resolution. In addition, several individual lifetimes can be resolved from a mixture of chromophores, allowing identification of different components that might have almost identical absorption and emission features. 

Luminescence decay curves may be observed by displaying the output of the photomultiplier on an oscilloscope. Precautions must be taken to correct for instrumental distortion of fast decay curves (D13). In multicomponent systems with differing decay times, electronic gating may be used to isolate the signal due to one component (time resolved phosphorimetry) (SI). A complete emission spectrum can be observed using a spectrograph with a photographic plate or television camera tube, but these systems are as yet only of specialist interest. 

Energies in the infrared spectrum are conventionally expressed in wave numbers, which are defined as the number of waves per centimeter, i.e., the reciprocal of the wavelength measured in centimeters. The infrared spectrum extends from 12,500 to 50 cm (i.e., a wavelength of 0.8-200 fjLia.) and the far infrared from 40-10 cm (260 p.m-1 mm), but the upper limit of most commercial instruments is about 200 cm (50 ixm). Spectra are most frequently obtained by absorption and reflection techniques, but polarization, emission, and luminescence are also used (C26). Similar components are used in all types of instrument. Reflection measurements of samples with low transmission are made in the near infrared with a conventional spectrophotometer fitted with a reflec-... 

Recent developments of pulsed light sources, optical components, fast and sensitive detectors and electronic equipment for data collection and analysis have permitted the construction of numerous instruments, often commercially available, for the collection of luminescence data with excellent resolution in time, spectral distribution and space. The sensitivity has reached the ultimate level that allows the characterization of such properties for single molecules (see Section 3.13). Only an overview of some of these techniques is given here. 

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