Luminescence instrumentation characteristics

In general, luminescence measurements are relative rather than absolute, since the Instrument characteristics and sample properties that determine the fluorescence Intensities are often not well defined. Absolute luminescence measurements are difficult to perform and require time and Instrumentation not available In most laboratories. Thus, luminescence measurements rely heavily on standards to determine Instrument responses and parameters, the chemical composition of samples, and the characteristics of chemical systems. To... 

Definition and Uses of Standards. In the context of this paper, the term "standard" denotes a well-characterized material for which a physical parameter or concentration of chemical constituent has been determined with a known precision and accuracy. These standards can be used to check or determine (a) instrumental parameters such as wavelength accuracy, detection-system spectral responsivity, and stability (b) the instrument response to specific fluorescent species and (c) the accuracy of measurements made by specific Instruments or measurement procedures (assess whether the analytical measurement process is in statistical control and whether it exhibits bias). Once the luminescence instrumentation has been calibrated, it can be used to measure the luminescence characteristics of chemical systems, including corrected excitation and emission spectra, quantum yields, decay times, emission anisotropies, energy transfer, and, with appropriate standards, the concentrations of chemical constituents in complex S2unples. 

Detecting the presence of small, even invisible, amounts of blood is routine. Physical characteristics of dried stains give minimal information, however, as dried blood can take on many hues. Many of the chemical tests for the presence of blood rely on the catalytic peroxidase activity of heme (56,57). Minute quantities of blood catalyze oxidation reactions between colorless materials, eg, phenolphthalein, luco malachite green, luminol, etc, to colored or luminescent ones. The oxidant is typically hydrogen peroxide or sodium perborate (see Automated instrumentation,hematology). 

Room-temperature fluorescence (RTF) has been used to determine the emission characteristics of a wide variety of materials relative to the wavelengths of selected Fraunhofer lines in support of the Fraunhofer luminescence detector remote-sensing instrument. RTF techniques are now used in the compilation of excitation-emission-matrix (EEM) fluorescence "signatures" of materials. The spectral data are collected with a Perkin-Elraer MPF-44B Fluorescence Spectrometer interfaced to an Apple 11+ personal computer. EEM fluorescence data can be displayed as 3-D perspective plots, contour plots, or "color-contour" images. The integrated intensity for selected Fraunhofer lines can also be directly extracted from the EEM data rather than being collected with a separate procedure. Fluorescence, chemical, and mineralogical data will be statistically analyzed to determine the probable physical and/or chemical causes of the fluorescence. 

Instrumentation and methods currently available provide limited means for realtime measurements of the continuous wave (CW) and transient characteristics of luminescent substances. The measurement, in real time, of the spatial distribution of a parameter of interests, for instance, in cells and in tissue cannot be attained with present technology. Optical fibers are used to monitor the response of a sensor in limited regions in space. 

The book starts with a short introduction to the fundamentals of optical spectroscopy, (Chapter 1) describing the basic standard equipment needed to measure optical spectra and the main optical magnitudes (the absorption coefficient, transmittance, reflectance, and luminescence efficiency) that can be measured with this equipment. The next two chapters (Chapters 2 and 3) are devoted to the main characteristics and the basic working principles of the general instrumentation used in optical spectroscopy. These include the light sources (lamp and lasers) used to excite the crystals, as well as the instrumentation used to detect and analyze the reflected, transmitted, scattered, or emitted light. 

However, luminescence lifetime, which is a measure of the transition prob-abihty from the emitting level, may be effectively used. It is a characteristic and unique property and it is highly improbable that two different luminescence emissions will have exactly the same decay time. The best way to determine a combination of the spectral and temporal nature of the emission is by using laser-induced time-resolved spectra. The time-resolved technique requires relatively complex and expensive instrumentation, but its scientific... 

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. 

As reviewed in the introduction, the luminescence from polymers and biopolymers may be described in terms of spectral shape, quantum yield of emission, decay time characteristics and polarization properties. The recent rapid increase in interest in the usefulness of luminescence techniques to study the structure and prtqwrties of molecular systems is partly due to the now ready availability of reliable instrumentation. Although the apparatus necessary for studying the spectral characteristics of luminescence is well established and has been r iewed in detail by several authors there have been recent rapid developments in the techniques available for time-... 

Luminescence intensity (II) is the main measured parameter that depends on a number of factors related to the instrument, measurement conditions, luminophore characteristics, and sample properties. In dilute solutions, its relationship with the concentration of luminophore is as follows ... 

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