Luminescent materials probes

CL is the only contaedess method (in an electron probe instrument) that provides microcharacterization of electronic properties of luminescent materials. 

Even if few systems are proposed for inorganic compounds (with regard to the number of potential pollutants), instruments or sensors for parameters used for treatment process control are available UV systems for residual chlorine in deodorization, electrochemical sensors for dissolved oxygen (with nowadays a luminescent dissolved-oxygen probe utilizing a sensor coated with a luminescent material) and a colorimetric technique for residual ozone. 

The fluorescence and phosphorescence of luminescent materials are modulated by the characteristics of the environment to which these materials are exposed. Consequently, luminescent materials can be used as sensors (referred also as transducers or probes) to measure and monitor parameters of importance in medicine, industry and the environment. Temperature, oxygen, carbon dioxide, pH, voltage, and ions are examples of parameters that affect the luminescence of many materials. These transducers need to be excited by light. The manner in which the excited sensor returns to the ground state establishes the transducing characteristics of the luminescent material. It is determined by the concentration or value of the external parameter. A practical and unified approach to characterize the luminescence of all sensors is presented in this chapter. This approach introduces two general mechanisms referred as the radiative and the nonradiative paths. The radiative path, in the general approach, is determined by the molecular nature of the sensor. The nonradiative path is determined by the sensor environment, e.g., value or concentration of the external parameter. The nonradiative decay rate, associated with the nonradiative path, increases... 

Some applications other than laser materials are the following luminescent materials for lighting, for display in cathode-ray tubes, and for X-ray radiography scintillator materials electroluminescent thin films glasses for solar concentrators colored materials for all types of applications (e.g., pigments). The greater part of these applications were reviewed in refs. 2 and 3. Optical centers can in many cases also be used as probes of the surroundings. 

The unique luminescent properties of rare earth metal clathrochelates have been used in the development of luminescent materials (luminophores and laser materials). The luminescence of these clathrochelates in solution makes their application as biological probes and concentrators of the luminescence (i.e., the antenna effect ) promising. These complexes can also serve as efficient molecular devices to convert UV light absorbed by the ligand to lanthanide ion luminescence in the visible region. Even in very dilute (10-5 mol l-i) solutions, the conversion of irradiated photons to luminescent ones has been observed to occur at a rate of approximately 1%. For rare earth metal aqua ions at the same concentration, the efficiency of conversion is equal to 4 x IQ- % [212, 390-392]. 

We discuss under this heading the use of fluorescence polarization methods to study the order In polymers, particularly In drawn fibrous materials and, by association, the use of such ordered systems to study fundamental details of the luminescence of probe molecules, the use of polarization methods to study rotational motion In polymers In solution, and the temperature dependence of luminescence as a probe of subgroup motion. 

The use of luminescent ions as a probe does nut belong to the field of industrial application of luminescent materials, but should be considered as an application in the field of research and characterisation of materials. The basic idea is that the luminescence properties of an ion tell us something about the ion itself and also about its surroundings in the host lattice. The dangerous side of this use of luminescence, a side which is often overlooked, is that only luminescent ions can be monitored. However, it may well be that the material contains the specific ion but that it does not or only partly luminesce under the given circumstances. It is therefore important to know whether the ion has really been excited or not, and whether all ions show emission or not. 

Luminescent Materials, p. 816 Luminescent Probes, p. 821 Semiochemistry, p. 1270 Supramolecular Photochemistry, p. 1434... 

Eluorescence Sensing of Anions, p. 566 Imaging and Targeting, p. 687 Ion-Selective Electrodes, p. 747 lonophores, p. 760 Lariat Ethers, p. 782 Luminescent Materials, p. 8i(5 Luminescent Probes, p. 821 Molecular-Level Machines, p. 93 ... 

In most examples presented above, the sensing function is based on changes in the intensity of one transition, which can be heavily affected by the quantity of the luminophore, excitation power, and the drifts of the optoelectronic system. Thus, the comparison of the emission of different samples based on the detected intensity may lead to erroneous conclusions. Although the measurements of quantum yields and/or lifetime are affected neither by the intensity of the excitation source nor by the probe concentration, they require a relatively long time and the computational treatment. The utilizing of the ratio between the intensity of two transitions of the same luminescent material, instead of only one transition, can overcome the main drawbacks of the intensity-based measurements of only one transition. The ratiometric... 

Fluorescent materials have important applications in medical research. Dyes such as fluorescein are attached to protein molecules to probe biological reactions. Fluorescent materials, such as sodium iodide and zinc sulfide, can be activated by radioactivity and are used in scintillation counters to measure radiation (see Chapter 18). Light-emitting diode (LED) displays also use luminescent materials. 

Until relatively recently, most work focused on organic luminophores as sensor-probe materials. However, luminescent transition metal complexes, especially those with platinum metals (Ru(II), Os(II), Re(I), Rh(III), and Ir(III)) have shown considerable promise and are receiving increasing attention. More recently Pt(II) complex have shown promising results.(4) Many of these materials have highly desirable features ... 

We now present several useful, or potentially useful, systems based on luminescent metal complexes in organic or inorganic supports. The probe molecules were chosen based on the above guidelines. Each probe is supported in some way by a second material to produce a practical device. The results presented show how metal complexes can be applied to diverse problems. These results also identify some problem areas with polymeric supports. We discuss some of our insights into the design and modeling of such systems and describe measurements that help unravel these complex systems. 

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