Ir luminescent

In this chapter, spectroscopy is an umbrella term for a variety of complementary methods such as tJV/VIS, IR, luminescence, and NMR, with the object of examining mainly polymer additives in solution after extraction but usually before a chromatographic separation. On-line spectroscopic detection hyphenated to chromatography is dealt with in Chapter 7. 

TGA, iodometric, mid-IR, luminescence (fluorescence and phosphorescence) and colour formation (yellowness index according to standard method ASTM 1925) were all employed in a study of aspects of the thermal degradation of EVA copolymers [67], Figure 23 compares a set of spectra from the luminescence analysis reported in this work. In the initial spectra (Figure 23(a)) of the EVA copolymer, two excitation maxima at 237 and 283 nm are observed, which both give rise to one emission spectrum with a maximum at 366 nm weak shoulders... 

A hydrogen termination of the crystallite surface is assumed in most studies. Calculations show that a small part of the hydrogen can be removed without the formation of DBs, as shown for the transformation of Si29H36 to SijjH [Hi-4-]. Further dehydrogenation, however, leads to the formation of DBs that are efficient recombination centers and thus effectively suppress the luminescence [De2, Hi4, De5]. The observed IR luminescence has been proposed to be due to recombination via DB centers [De3]. 

Fig. 4.3. a-c Laser-induced time-resolved IR luminescence spectra of apatite demonstrating Nd ", Yb " andMn " centers... 

IR luminescence lines with relatively short decay times connected with Nd are very strong in the fluorite emission spectrum (Fig. 4.11c,d). Besides that, UV and violet hnes with a short decay time appear, which are ascribed to Nd (Fig. 4.11a,b). 

Figures 4.34a,b demonstrate the emission lines of titanite, which according to their spectral positions may be confidently connected with Nd " ". The luminescence spectrum in the 860-940 nm spectral range, corresponding to the transition, contains six peaks at 860, 878, 888, 906, 930 and 942 nm, while around 1,089 nm corresponding to F3/2- fn/2 transition it contains five peaks at 1,047,1,071,1,089,1,115 and 1,131 nm. The decay time of IR luminescence of Nd " equal to approximately 30 ps in titanite is evidently the shortest one in the known systems activated by Nd ". The typical radiative lifetime of this level depends on the properties of the solid matrix and varies from approximately 100 ps to 600 ps (Kaminskii 1996). To explain the fast decay time of Nd " in titanite, the energy level quenching by the host matrix may be considered.

IR luminescence of in minerals has been detected in steady-state lumines-... 

Luminescence of in minerals was proposed in tsavorite where the broadband IR luminescence with a short decay time less than 1 ps was associated with this center (Mazurak and Czaja 1996). The luminescent level has been identified as a component of the 82 CT2g) energy level. At least two different V sites are detected. 

IR luminescence detected in ZrSi04-Cr has an excitation band peaking at 920 nm. Its luminescence spectrum at 300 K (Fig. 5.38) is characterized by a relatively unresolved broad band peaking at 1,200 nm. It is very similar to Cr luminescence in silicates, especially in forsterite except for a very short decay time shorter than the time resolution of our detection system about 200 ns. It is not suitable for Cr with a much longer decay in the ps range (Boulon 1997). Luminescence at lower temperatures is much more intensive and spectra are characterized by several strong narrow hnes with very short decay which appear already at 100 K. Once again, it is rather unusual for Cr +. 

Luminescence of Mn " " was not detected in minerals yet, but is well known in phosphors. The first possibility will be barite (Fig. 5.39), because BaS04-Mn has IR luminescence and is considered as a potential material for a tunable NIR laser (Brunold and Giidel 1997 Brunold et al. 1997). 

Luminescence of monovalent Pb was proposed for explanation of an IR luminescence band peaking at 860 nm in the emission spectrum of feldspars (Kusnetsov and Tarashchan 1988). 

Miller, T.A., Jeffery, J.C., Ward, M.D., etal. (2004) Photoinduced Ru-Yb energy transfer and sensitised near-IR luminescence in a coordination polymer containing co-crystallised [Ru(bipy)(CN)4]2- and Yb(lll) units. Dalton Transactions, 1524. 

The Xa method has been used as a tool for structure elucidation of some short lived tramsients such as [PtCl,], [PtCls] , amd [PtCl l", generated by pulse radiolysis or flash photolysis. Measurements of the IR luminescence amd absorption... 

A new chemical source of singlet molecular oxygen ( Oj, Ag), H20 /Ca(0H)2, has been investigated in detail. First, the formation of O2 has been proved unambiguously by resorting both to the specific detection of the IR luminescence at 1270 nm of O2 and to the chemical trapping of the excited species with a new cationic water-soluble trap. The process has been shown to be catalytic and the influence of several parameters (pH, concentrations and purities of reactants) on the initial rate of O2 formation has been examined. Finalfy, the ability of the system H202/Ca(0H)2 to oxidize various water-soluble electron-rich substrates has been assessed. 

For these reasons, we have undertaken a detailed study of this system by confirming, in a first step, the generation of O2 by chemical trapping and by detection of its specific IR-luminescence. Then, the kinetics of the reaction were examined by studying the influence of several parameters such as pH and concentrations and purities of reactants on the initial rate of O2 formation. Finally, the ability of this system to oxidize various water-soluble electron-rich substrates such as polycyclic aromatic, cyclohexadienic and acrylic derivatives was assessed. 

The parameter fcA is the bimolecular rate constant for deactivation by the solvent and is thus defined by Eq. (20) and straightforwardly determined by measurement of kd in the neat solvent by time-resolved IR luminescence measurements. It was recognised that fcA is a linear function of the concentration of hydrogen (or deuterium) atoms in the liquid and can be obtained by summing together the contributions of all the individual types of bonds, C-H, O-H, C-D, O-D and so on, present in the molecule. This leads to the establishment of the relationship of Eq. (21)... 

Figure 6. Plot of the first-order constant for Ojf Aj) IR luminescence decay in benzene as a function of the concentrations of DABCO ( ) and DABCO-2HI2(A).

Figure 11. Arrhenius plots for the quenching of 02C J in toluene by (a) /1-carotene, (b) strychnine, and (c) DPBF. Inset typical single shot 02( Ag) IR luminescence decay profile in the presence of DPBF (1.07 x 10 4 mol l-1) at — 77°C timescale 5 /is/division. From [39] with permission. Copyright 1988, American Chemical Society.

LaEu(XXXI)(N03)4-2H20 Whitish yellow /ieff = 3.5/Tb IR luminescence spectrum [5]... 

All tetrametallated porphyrins dealt with in this section have been extensively characterized by electrochemical and various spectroscopic techniques such as NMR, IR, luminescence, and UV-Vis, among others. But, the following discussion will be focused mainly on the electrochemistry, spectroelectroche-mistry, and electronic spectroscopy, and the evaluation of the electronic coupling between the components of the peripherally metallated porphyrins. This is an important parameter for the discussion of the catalytic and electrocatalytic properties as shown below. 

The optical behavior of papers under filtered light examination and ultraviolet (UV)-visible (or visible-infrared (IR)) luminescence is also an important characteristic that helps to differentiate them. Absorption spectroscopy can be used to measure and compare the color of papers. 

TLC is used extensively for the study of inks in many types of case, particularly those involving forgery of cheques. The comparison and discrimination that may be obtained is in terms of both the visible dyestuffs and the ultraviolet (UV)-fluores-cent components that are present. A number of methods are available for the comparison of the color of ink and these include microscopy, IR luminescence and reflectance, and also TLC. Ink colors can change rapidly when the writing is exposed to light and this tends to complicate the results obtained by microscopic examination, while... 

IR luminescence may be affected by the exposure of the ink to moisture and many common household chemicals. 

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