Common Luminescence Experiments

The most common starting point in the characterisalion of luminescent lanthanide systems is UV-visible-NlR electronic absorption spectroscopy. The UV-visible-NlR spectrum, in 

In an excitation spectram a single emission detection wavelength (2em) is chosen that coincides with an observed band in the emission spectram. The excitation source is then 

T is the measured luminescence lifetime and 7q is the intensity at f = 0. In general the emission decay curves are analysed according to this model to extract the measured lifetime values. Deviations from this simple, single-exponential decay behaviour then reflect the presence of multiple emissive species in the sample, sample inhomogeneity, and/or more complex excited state decay processes. An example of a luminescence lifetime determination is provided in Fig. 2.3. 

2A Time-resolved Luminescence Emission and Excitation Spectra 

3 Basic Design Elements and Conflgurations in Luminescence Spectrometers 

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Recombination is either radiative or non-radiative. The radiative process is accompanied by the emission of a photon, the detection of which is the basis of the luminescence experiment. The radiative transition is the inverse of optical absorption and the two rates are related by detailed balance. Non-radiative recombination is commonly mediated by the emission of phonons, although Auger processes are sometimes important, in which a third carrier is excited high into the band. The thermalization process occurs by the emission of single phonons and is consequently very rapid. Non-radiative electron-hole recombination over a large energy requires the cooperation of several phonons, which suppresses the transition probability. 

The substances involved in bioluminescence reactions are usually unstable. Thus, the extraction and purification of bioluminescent substances should be carried out in the shortest possible period of time, usually at a low temperature. It is known through experience that luminescent substances are almost always more stable in the original animal tissues than in extracts when preserved at a low temperature. Therefore, before starting extraction and purification, the stability of the extracts and purified substances should be investigated by carrying out a small-scale pilot experiment. A pilot experiment is also essential in the course of purification to avoid an unexpected loss of the target substance. If a component of the luminescence system is insoluble in common buffer solutions, it must be solubilized to purify it (see C1.3). 

Knowledge of the sample pressure is essential in all high-pressure experiments. It is vital for determinations of equations of state, for comparisons with other experimental studies and for comparisons with theoretical calculations. Unfortunately, one cannot determine the sample pressure directly from the applied force on the anvils and their cross-sectional area, as losses due to friction and elastic deformation cannot be accurately accounted for. While an absolute pressure scale can be obtained from the volume and compressibility, by integration of the bulk modulus [109], the most commonly-employed methods to determine pressures in crystallographic experiments are to use a luminescent pressure sensor, or the known equation of state of a calibrant placed into the sample chamber with the sample. W.B. Holzapfel has recently reviewed both fluorescence and calibrant data with the aim of realising a practical pressure scale to 300 GPa [138]. 

Other Minerals Up to this point, reference has been made to other luminescing phases within meteorites but in all cases no systematic studies have been reported to 1) determine the cause of the CL or 2) to relate the CL to the genesis of the mineral or meteorite. The following comments are made to draw attention to the possible significance of CL observations in other meteoritic minerals most observations are from the author s personal experience and have not been documented. Oldhamite is a rare mineral in the enstatite chondrites but is known to carry appreciable quantities of rare earth elements (REE). The CL spectra have not been studied in detail but visual CL is yellow and a CL emission at 580nm was reported (H) but with rapid intensity change under the electron beam. A REE activator of the CL is possible. Hibonite is a relatively common... 

This procedure can be adjusted for other volumes or concentrations, accordingly. Your goal is to determine how various metal ions affect HQS luminescence. Consider interesting comparisons of different metal ions that may commonly be found together in biolo-gical/medical applications, in the environment or in industrial settings. See for example, Experiment 7.5. 

Similar time resolved techniques to study a host of transfer phenomena such as sensitization of luminescence, cross relaxation and optical trapping have been developed (Yen 1986b). Time resolved absorption or hole burning experiments are also possible but have been less common. In all of the above, the pulse length... 

Chapter 13, using polarised exciting light. Examination of the depolarisation of the resulting luminescence allows orientation of a specific chromophore to be selected and its rotation studied. This can be done in steady state experiments which yield the amount of rotation of the excited state during its lifetime. More informative are time dependent observations of the polarised and depolarised emissions. Unfortunately, most common polymers do not have chromophores that can easily be studied in this way. Luminescent probes can be attached to the polymer backbone and these used to monitor the motion. However, such measurements usually indicate the way in which the probe is attached to the polymer rather than the intrinsic motion of the polymer chain. 

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