Time-resolved spectroscopy luminescence techniques

Time-resolved luminescence spectroscopy may be extremely effective in minerals, many of which contain a large amount of emission centers simultaneously. With the steady state technique only the mostly intensive centers are detected, while the weaker ones remain unnoticed. Fluorescence in minerals is observed over time range of nanoseconds to milliseconds (Table 1.3) and this property was used in our research. Thus our main improvement is laser-induced time-resolved spectroscopy in the wide spectral range from 270 to 1,500 nm, which enables us to reveal new luminescence centers in minerals previously hidden by more intensive centers. 

An identihcation of the nature of Cr luminescence in synthetic spinel by the line narrowing technique enabled to distinguish up to 25 different Cr + sites (Deren et al. 1996). Laser-induced time-resolved spectroscopy enables us to see typical for spinel emission of Cr ", while the different broadness of the spectral lines at different time windows demonstrates that different Cr " sites are present also in natural spinel (Fig. 4.51). 

Time dependent fluorescence depolarization is influenced by the exciton annihilation which occurs in confined molecular domains . Photoemission results from singlet exciton fusion as shown by the excitation intensity dependence which occurs in anthracene crystals. Reabsorption of excitonic luminescence is an effect which has been shown to occur in pyrene crystals. The dynamics of exciton trapping in p-methylnaphthalene doped naphthalene crystals involves phonon assisted detrapping of electronic energy. Ps time resolved spectroscopy was the experimental technique used in this work. 

The main luminescence parameters traditionally measured are the frequency of maximal intensity Vmax, intensity I, the quantum yield < >, the hfetime of the exited state T, polarization, parameters of Raman spectroscopy, and excited-state energy migration. The usefulness of the fluorescence methods has been greatly enhanced with the development of new experimental techniques such as nano-, pico-, and femtosecond time-resolved spectroscopy, single-molecule detection, confocal microscopy, and two-photon correlation spectroscopy. 

The natural kyanite in our study consisted of 30 samples. Concentrations of several potential impurities luminogens are presented in Table 4.17. Laser-induced time-resolved technique enables to detect all lines and bands previously found evidently connected to different kinds of Cr " luminescence (Fig. 4.107). Mn bearing orange kyanite was smdied by laser induced time resolved spectroscopy (Fig. 4.108). Broad band peaking at 760 nm excited by 355 nm has t = 550 ps. It... 

In the proposed book there is an emphasis cm luminescence lifetime, which is a measure of the transition probability and non-radiative relaxation from the emitting level. Luminescence in minerals is observed over a time interval of nanoseconds to milliseconds. It is therefore a characteristic and a unique property and no two luminescence emissions will have exactly the same decay time. The best way for a combination of the spectral and temporal nature of the emission can be determined by time-resolved spectra. Such techniques can often separate overlapping features, which have different origins and therefore different luminescence lifetimes. The method involves recording the intensity in a specific time window at a given delay after the excitation pulse where both delay and gate width have to be carefully chosen. The added value of the method is the energetic selectivity of a laser beam, which enables to combine time-resolved spectroscopy with powerful individual excitation. 

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

The same equipment, which is used for time-resolved Ivuninescence application is suitable for other laser-based spectroscopies. Thus several spectroscopic methods may be applied simultaneously. The most important techniques, which may be used together with time-resolved luminescence, are laser-induced breakdown spectroscopy, Raman spectroscopy and Second Harmonics Generation spectroscopy. 

The possibilities of time-resolved laser based spectroscopies have been demonstrated, combining such techniques as luminescence, Raman, breakdown and second-harmonic generation. Radiometric sorting of minerals using LIBS was patented and apparatus for evaluation of phosphate rocks with elevated dolomite content has been developed and constructed. 

The Introduction chapter contains the basic definitions of the main scientific terms, such as 5pectro5copy, luminescence spectroscopy, luminescent mineral, luminescent center, luminescence lifetime, luminescence spectrum and excitation spectrum. The state of the art in the steady-state luminescence of minerals field is presented. The main advantages of the laser-induced time resolved technique in comparison with the steady-state one are shortly described. 

The Applications of Laser-induced Time-resolved Spectroscopic Techniques chapter starts with a short description of laser-induced spectroscopies, which may be used in combination with laser-induced luminescence, namely Breakdown, Raman and Second Harmonic Generation. The chapter contains several examples of the application of laser-based spectroscopies in remote sensing and radiometric sorting of minerals. The proljlem of minerals as geomaterials for radioactive waste storage is also considered. 

Most of the time-resolved emission spectroscopy setups are home made in the sense that they are built from individual devices (laser, detection system,. ..) hence they are not of a plug and press type, so that their exact characteristics may vary from one installation to the other. Some of these differences have no impact on the overall capabilities of the system but some have a drastic influence on the way the collected data are processed and analysed. This aspect will be detailed in the next section, while this section deals with a general description of the apparatus. The most basic type of apparatus will be described, with no reference to sophisticated techniques such as Time Correlated Single Photon Counting or Circularly Polarized Luminescence devices. 

Time-resolved emission spectroscopy is gaining importance in the study of various chemical aspects of luminescent lanthanide and actinide ions in solution. Here, the author describes the theoretical background of this analytical technique and discusses potential applications. Changes in the solution composition and/or in the metal-ion inner coordination sphere induce modifications of the spectroscopic properties of the luminescent species. Both time-resolved spectra and luminescence decays convey useful information. Several models, which are commonly used to extract physico-chemical information from the spectroscopic data, are presented and critically compared. Applications of time-resolved emission spectroscopy are numerous and range from the characterization of the... 

Although different synthetic approaches have been used, the experimental techniques employed to verify the properties of the systems are very often similar, and generally include steady-state and time-resolved absorption and luminescence spectroscopy. 

Luminescence spectroscopy, with its excellent sensitivity for trace analysis, has limited applicability for analysis of complex mixtures of organic molecules. The most successful techniques involve cryogenic temperatures with matrix isolation or nanosecond time resolving capability (13). While being highly selective techniques, they are not easily... 

During the year a number of specialized monographs of relevance to photophysics have appeared. Two of general interest deal with applications of time resolved optical spectroscopy and luminescence techniques in chemical and biochemical analysis. ... 

Time resolved evanescent wave induced fluorescence spectroscopy is a powerful method for the investigation of dye molecules at interfaces. This technique has been used on studies on the popular photosensidzer aluminium phthalocyanine tetra/sulphonate absorbed at fused silica/methanol interfaces . 2nd harmonic detection of sinusoidally modulated two photon excited fluorescence can also be used to obtain luminescence spectra ". ... 

V. Bruckner, K.-H.Feller, and U.-W.Grummt, Applications of Time-Resolved Optical Spectroscopy, Elsevier Science Publishers, Amsterdam, 1990. Luminescence Techniques in Chemical and Biochemical Analyses, ed. 

Fluorescence applied to oil identification has been an active field, with 17 papers presented on the subject at the last three Pittsburgh Conferences. A number of interesting developments for fluorescence and low-temperature luminescence (LTL) are described by Eastwood et al. (58). These include synchronous scanning, difference spectrofluorometry, synchronous difference spectroscopy, derivative spectroscopy, and total luminescence (or contour) spectroscopy and combinations of these techniques. In a recent presentation, Eastwood and Hendrick (59) reported an extension of their low-temperature luminescence studies to include polarized excitation and emission spectroscopy, and time-resolved phosphorescence. Preliminary studies of polarization effects indicate that differences exist in low-temperature polarized luminescence spectra of oils, which may aid in oil identification. In the time-resolved phosphorescence spectra of oils, the most significant difference observed was enhancement of the vanadyl porphyrin signal at approximately 700 nm for short delay times (20 fxsec). 

Several hetero-bischelated complexes of Ir(III) with 1,10-phenanthroline and substituted 1,10-phenanthroline have also been reported to have non-exponential luminescence decay curves (19). Although the individual emission spectra of the non-equilibrated levels of these complexes are again too close to resolve by conventional emission spectroscopy, partial resolution has been accomplished by time-resolved emission spectroscopy via box-car averaging techniques (20). Complete resolution has been accomplished by computer analysis of luminescence decay curves as a function of emission wavelength (20). In these complexes, the luminescent levels appear to arise from both ligand-localized ( tttt ) states and charge-transfer ( ) states. 

In our opinion the paper by Moses et al. [36] on the scintillation mechanisms in CeF.3 is a fine example of how scintillators should be studied from a fundamental point of view. A combination of techniques was u.sed, viz. (time-resolved) luminescence spectroscopy, ultraviolet photoelectron spectroscopy, transmission spectroscopy, and the excitation region was extended up to tens of eV by using synchrotron radiation. Further, powders as well as crystals with composition Lai-xCexFy were investigated,... 

After three decades of rapid development, time-resolved absorption and luminescence spectrometry emerged as powerful tools for studying the supramolecular behavior ot molecules and materials Such techniques provide complementdry information to steady state L,(V/Vis nuclear infrared spectroscopy, which may be used to study the supramolecular behavior in the ground state The general sensitivity ot time-correlated techniques combined with insight into the process dynamics and low... 

NN = polypyridyl ligands and L = stilbene-like ligands, in acetonitrile solution and in poly(methyl methacrylate) (PMMA) polymer film exhibited hypsochromic shifts as the medium rigidity increases due to the luminescence rigidochromic effect. Time-resolved IR (TRIR) spectroscopy, in combination with other techniques, characterized the excited-state electronic properties of the fac-[Re(CO)3(phen) (bpe)]PFa complex, where bpe is l,2-bis(4-pyridyl)ethylene. 

---