Total luminescence intensity

Selectivity The selectivity of molecular fluorescence and phosphorescence is superior to that of absorption spectrophotometry for two reasons first, not every compound that absorbs radiation is fluorescent or phosphorescent, and, second, selectivity between an analyte and an interferant is possible if there is a difference in either their excitation or emission spectra. In molecular luminescence the total emission intensity is a linear sum of that from each fluorescent or phosphorescent species. The analysis of a sample containing n components, therefore, can be accomplished by measuring the total emission intensity at n wavelengths. 

Assay of photoprotein. The activity of the photoprotein was measured in 1ml of 20 mM Tris-HCl buffer, pH 8.0, containing 0.6 M NaCl at room temperature. The intensity and total amount of light emitted were recorded. The luminescence intensity is markedly intensified by adding 5 il of catalase solution (crystalline bovine liver catalase 1.5 mg/ml) and 10 pi of 3% H2O2. 

Assay methods. Activity can be measured at pH 5.5 or at pH 8.0. With the same sample, the pH 5.5 method gives a much higher luminescence intensity than the pH 8.0 method (and, shorter reaction time), although the total amounts of light emitted by the two methods are practically equal (Fig. 9.4). The pH 5.5 method is susceptible to inhibition by various salts, whereas the pH 8.0 method is not affected. 

If a trace activity is indicated by the luminescence intensity measurement, the following two methods can be used to determine whether the light emission is due to the luciferase or it is an artifact (1) Measure the luminescence intensity with a buffer that contains 1 mM EDTA (add luciferase to this buffer and wait 1 min before mixing with luciferin). If the luminescence was caused totally by luciferase, the light intensity will be decreased to about 20% by EDTA (see Section 3.1.7). (2) Inactivate luciferase by acidifying the sample to pH about 2.0, followed by neutralization with NaHCC>3. Inactivated luciferase should not show any luciferase activity. 

Let N(j,Ni,N2, and Nj, be the equilibrium population densities of the states 0, 1,2, and 3, respectively (reached under continuous wave excitation intensity Iq), and let N = NQ + Ni+N2 + N3he the total density of optical absorbing centers. The up-converted luminescence intensity ho (corresponding to the transition 2 0) depends on both N2 and on the radiative emission probability of level 2, A2. This magnitude, which is dehned below, is proportional to the cross section a20 (called the emission cross section and equal to the absorption cross section ao2, as shown in Chapter 5). Thus we can write... 

Since the CL emission decreases upon treatment of polypropylene with peroxide-destroying agents, such as sulphur dioxide, it was concluded that the emission originated from hydroperoxides present in the material [28]. The area under the CL emission peak is denoted total luminescence intensity (TLI) and has been found to be proportional to the hydroperoxide concentration in the early stages of the oxidation of polypropylene [28]. 

The /3-diketonate [Nd(dbm)3bath] (see figs. 41 and 117) has a photoluminescence quantum efficiency of 0.33% in dmso-7r, solution at a 1 mM concentration. It has been introduced as the active 20-nm thick layer into an OLED having an ITO electrode with a sheet resistance of 40 il cm-2, TPD as hole transporting layer with a thickness of 40 nm, and bathocuproine (BCP) (40 nm) as the electron injection and transporting layer (see fig. 117). The electroluminescence spectrum is identical to the photoluminescence emission the luminescence intensity at 1.07 pm versus current density curve deviates from linearity from approximately 10 mA cm-2 on, due to triplet-triplet annihilation. Near-IR electroluminescent efficiency <2el has been determined by comparison with [Eu(dbm)3bath] for which the total photoluminescence quantum yield in dmso-tig at a concentration of 1 mM is Dpi, = 6% upon ligand excitation, while its external electroluminescence efficiency is 0.14% (3.2 cdm-2 at 1 mAcm-2) ... 

Very recently the research groups of Professor F. S. Richardson at the University of Virginia, and Dr. H. P. J. M. Dekkers of the University of Leiden have built instruments capable of measuring the time dependence of the CPL intensity [14-24], As is evident from eqs. (8) and (9), for the simple system described in the previous section, in which we assumed no competing excited state processes, the time dependence of the CPL intensity would be exactly equal to that measured for the total luminescence intensity. Time-resolved CPL (TRCPL) is, therefore, an experiment suited for the study of excited state processes that result in optical activity changes. We will summarize here the theoretical formalism for two such processes, namely, excited state racemization, and excited state enantioselective quenching. 

The total luminescence intensity is the product of the number of excited electron-hole pairs and the recombination rate, N /x. If tIl is the luminescence quantum efficiency and G is the excitation intensity, then by definition, t i, G is the luminescence intensity. is the density of states which are occupied by electron-hole pairs. Since cannot be greater than the available density of states at the emission energy, then it follows from Eq. (8.30) that... 

Analysis of the decay of luminescence intensity with time has been shown to be related to the mechanism of the annihilation process (i.e., direct fluorescence from singlets or luminescence resulting from triplet-triplet annihilation). Feldberg developed simulation techniques for intensity-time profiles from potential step experiments, relating the emission rate (photons/s) to the total redox rate N (moles/s) [40]. 

Fig. 1 depicts a characteristic time-resolved Cu" emission spectrum of Cu-ZSM-5 with two main bands at 480 and 540 nm with different decay times. It evidences different defined Cu sites. Very low intensity bands at 450 and 605 nm (Fig. 5) have been shown to correspond additional defined Cu site and Cu bonded via Si-OH, resp. (9). The intensity of the band at 605 nm had never exceed 3% of the total spectrum intensity and is neglected in the spectra analysis. A lifetime of 5 s was chosen for the spectra evaluation note the importance of the luminescence lifetime for the spectra monitoring, cf Fig. 1. It is suppossed that the Cu luminescence intensity is proportional to the number of the corresponding Cu sites and the saturation of the luminescence intensity is not expected. Zeolites with the Cu/Al ratio below 0.5 were used for luminescence intensity calibration. The relationship between the Cu content in the zeolite and the intensities of the individual bands at 450, 480 and 540 nm (for Cu-ZSM-5) is...

Fig. 11a, b Time-resolved luminescence intensity of [Cr(bpy)3]3+ following pulsed excitation of [Cr(ox)3]3- in [Rh1 yCry(bpy)3][NaAl1 xCrx(ox)3]C104 at 1.5 K a the decomposition of the total luminescence into the fast and the slow component of the energy transfer process, (continuous line) experimental, (dashed line) calc using the shell model b rise of the fast component of the energy transfer (adapted from [27])... 

As Nres as well as Rc are functions of the homogeneous linewidth, nm, too, can be expressed as a function of Thom- This is shown in Fig. 21. Using the above value for rhom of 0.02 cm 1 for the fully concentrated compound, the concentration of resonant species at the centre of the distribution Nreswl019 cm"3. Together with the corresponding value of Rc of 34 A, nm takes on a value of 1.7. This is sufficient to result in the observed quantum efficiency of the first transfer step for irradiation near the centre of the distribution of close to 90% as derived from the ratio of the resonant peak to the total luminescence intensity. 

This phenomenon was observed with polymers some years ago [177—183]. The more recent investigations are due to Buben and Nikolskii [183]. These workers measured the emission from many amorphous and crystalline polymers and observed correlations between the temperature corresponding to the glow peak maxima and the structural transition temperatures of the materials. A detailed study of polyethylene thermoluminescence was made by Charlesby and Partridge [184]. The glow curve obtained after irradiation in vacuo possesses three peaks, a, j3 and y, whose luminescence intensities are proportional to the irradiation dose for doses below 5 x 104 rads. The maxima occurs, respectively, at —110, —65 and —27°C, when the total... 

Just as in ordinary luminescence measurements, the determination of absolute emission intensities is quite difficult, so it is customary to report CPL measurements in terms of the ratio of the difference in intensity, divided by the average total luminescence intensity... 

Note that we have a superscript, n, to indicate the polarization of the excitation beam, and also added a subscript to the lineshape function. As indicated above all CPL measurements are made relative to the total luminescence intensity which we may express using similar formalism as... 

The D-A transfer can speed up the decay of D in its excited state and thus shorten the decay time of D. As a result, r/g can also be obtained from the decay curve of the D luminescence after flash excitation of D. The decay curve represents the decay of transient luminescence intensity, which can be regarded as the number of photons emitted per time at time t. Denote the D-luminescence decay function by Io(t) for the absence of A and by I t) for the presence of A. The decay function can be obtained by normalizing the initial intensity of the experimentally measured luminescence decay curve, meaning 7o(0) = 7(0) = 1. The integrals of the intensity-decay function over time are proportional to the number of total photons emitted after excitation, i.e., it is just the measure of the steady-state luminescence intensity. From Eqs. (3.1) and (3.2), one thus has [4]... 

Drastic change takes place in luminescence spectrum of titanite at low temperatures (Fig. 4.80d). At 77 K, Nd luminescence intensity becomes lower and narrow line appears at 732 nm with long decay time of 2.5 ms accompanied by phonon repetitions. At even lower temperature of 20 K such emission totally dominates luminescence spectrum. Such behavior may be explained by Cr in intermediate crystal field sites for which the crystal field parameters lie in the crossing region of the T2 and states. Within the intermediate crystal field there is complicating mixing between doublet and quartet states with complicated spectra, non-radiative transfer and the temperature dependence of luminescence. In such case the emission from both T2 and E states may be expected. At 300 K the... 

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