Time luminescence spectra

Figure 9.4 Two-photon absorption-induced luminescence of CdTe QDs in D2O and H2O obtained from the luminescence spectrum as a function of time. The diameter and solvent are (a) 4.5 nm in D2O, (b) 3.7 nm in D2O, (c) 4.5 nm in H2O,...

Silica makes up 12.6 mass-% of the Earth s crust as crystalline and amorphous forms. It was found that both modifications show similar main luminescence bands, namely a blue one centered at 450 nm ascribed to which substitutes for Si, red centered at 650 nm linked with non-bridge O, and dark-red at 700-730 nm linked with Fe. Time-resolved luminescence of hydrous volcanic glasses with different colors and different Fe, Mn, and H2O contents were measured and interpreted (Zotov et al. 2002). The blue band with a short decay time of 40 ns was connected with T2( D)- Ai ( S) and Ai C G)- Ai ( S) ligand field transitions of Fe " ", the green band with a decay time of approximately 250 ps with a Ti( G)- Ai( S) transition in tetrahedrally coordinated Mn ", while the red band with a much longer decay time of several ms with T1 (4G)- Ai( S) transitions in tetrahedrally coordinated Fe ". We detected Fe " " in the time-resolved luminescence spectrum of black obsidian glass (Fig. 4.43d). 

Fig. 4.66. Laser-induced excitation (1) and luminescence spectra of natural silver halides (2,3-cerargerite, 4-embolite, 5-bromargeritechlorargyrite and embolite) (a) upper -300 K (b) 77 K (c) middle -time-resolved spectra with zero delay time (1) and delay time of 150 ns (2) (Gaft et al. 1989b). (d) bottom -laser-induced time-resolved luminescence spectrum of chlorargyrite under 355 nm excitation...

Representative time-resolved luminescence spectrum is given in Fig. 4.68. 

The presence of Pr in apatite samples, up to 424.4 ppm in the blue apatite sample, was confirmed by induced-coupled plasma analysis (Table 1.3). The luminescence spectrum of apatite with a broad gate width of 9 ms is shown in Fig. 4.2a where the delay time of500 ns is used in order to quench the short-lived luminescence of Ce + and Eu +. The broad yellow band is connected with Mn " " luminescence, while the narrow lines at 485 and 579 nm are usually ascribed to Dy and the fines at 604 and 652 nm, to Sm +. Only those luminescence centers are detected by steady-state spectroscopy. Nevertheless, with a shorter gate width of 100 ps, when the relative contribution of the short lived centers is larger, the characteristic fines of Sm " at 652 nm and Dy + at 579 nm disappear while the fines at 485 and 607 nm remain (Fig. 4.2b). It is known that such luminescence is characteristic of Pr in apatite, which was proved by the study of synthetic apatite artificially activated by Pr (Gaft et al. 1997a Gaft... 

Luminescence spectrum of scheelite with a broad gate width of 9 ms is shown in Fig. 4.9d. The narrow lines at 490 and 572 nm are usually ascribed to Dy and the lines at 607 and 647 nm to Sm " ". Nevertheless, the relative intensity of the line at 607 nm compared to the line at 647 nm is lower at longer delay times (Fig. 4.9e,f). Besides that with a shorter gate width of 1 ps, when the relative contribution of the short lived centers is bigger, the characteristic lines of Sm " " at 647 nm and Dy " at 575 nm disappear while the lines at 488 and 607 nm remain. Such luminescence is characteristic of Pr ", which was confirmed by a time-resolved luminescence study of scheelite artificially activated by Pr " and Sm " (Fig. 5.5). Unlike in apatite, the phenomenon exists not only under 308 nm, but also under 337 nm excitation due to the higher energy... 

Narrow lines at 462, 476, 482, 501 and 590 nm in the luminescence spectrum of the Ca-variety of garnet (grossular) with a relatively short decay time are not typical for traditional trivalent REE in minerals. Evidently they may be connected to visible emission of Nd (Fig. 4.57c,d), but this has to be checked. 

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.

Another group of lines is detected in the titanite luminescence spectrum, which may be considered as connected with the Nd " " emission. Those lines at 589, 658, 743 and 846 nm are especially strong in the luminescence spectra with a narrow gate excited by Aex = 532 nm (Fig. 4.34b). Such a combination of emission lines with relatively short decay times is very unusual for minerals and may not be easily connected to any rare-earth element traditional for luminescence in the visible range. If we were to consider the possible connection with the visible emission of Nd " ", the detected lines correspond very well, for example, to electron transitions from 67/2 level to %/2> fii/2> fi3/2 and Ii5/2 levels. 

Trivalent samarium activated minerals usually display an intense luminescence spectrum with a distinct hne structure in the red-orange part of the spectrum. The radiating term 65/2 is separated from the nearest lower level 11/2 by an energy interval of 7,500 cm This distance is too large compared to the energy of phonons capable to accomplish an effective non-radiative relaxation of excited levels and these processes do not significantly affect the nature of their spectra in minerals. Thus all detected lines of the Sm " luminescence take place from one excited level and usually are characterized by a long decay time. 

The line at approximately 600 nm has a long decay time of 1 ms. It is the strongest one in the titanite luminescence spectrum under 266, 355 and 532 nm (Fig. 4.33b,c), but its relative intensity is much lower under 514 nm excitation (Gaft et al. 2003b). It appears that from all lines found in titanite luminescence spectra only two weaker ones at 563 and 646 nm have similar kinetic and excitation characteristics with the line at 600 nm. Such a combination of luminescence lines is very typical for Sm ". Thus the emission spectrum... 

The narrow band at 437 nm with a decay time of 650 ns in the danburite luminescence spectrum belongs to Eu " luminescence (Fig. 4.15a), which was also detected by steady-state spectroscopy (Gaft et al. 1979). Besides that, under 308 nm excitation narrow lines appear at 580, 592, 611, 618, 655 and 692 nm (Eig. 4.15c) with a long decay time, which confidently may be ascribed to Eu. Under 266 nm excitation another group of hnes appear with the main line at 575 nm connected with a different type of Eu " (Fig. 4.15d). 

A possible candidate may be Tm ". For example, the doublets at 803 and 817 nm and at 796 and 813 nm are the strongest ones in cathodoluminescence spectra of fluorite and scheelite activated by Tm " (Blank et al. 2000). It is possible to suppose that the strong fines at 805 and 820 nm with a relatively short decay time of 60 ps in the titanite luminescence spectrum belong to Tm " ". They appear under 532 nm excitation and are evidently connected with the electron transition. Similar emission of Tm " was also detected in... 

As was already mentioned, the narrow lines at 692 and 710 nm in the luminescence spectrum of zoisite have been connected with element emission, while Cr and were considered as the possible candidates (Koziarsca et al. 1994). Laser-induced time-resolved luminescence spectra of zoisite reveal the same lines (Fig. 4.59). We are inclined to connect these lines with for the reason that vanadium concentration in our sample is much higher than the chromium concentration. 

Luminescence similar to those in zoisite has been found in the laser-induced time-resolved spectrum of chrysoberyl (Fig. 4.54d). A relatively broad band accompanied by narrow lines at 698,703 and 717 nm with a decay time of 150 ps, which are not connected with Cr emission, may be preUminary ascribed to V luminescence. 

The broad band peaking at 730 nm accompanied by a narrow doublet at 692 and 694 nm (Fig. 4.52) with a mutual decay time of 100 ps in the laser-induced time-resolved luminescence spectrum of beryl is not similar to the Cr emission in emerald. Thus we suppose that such typical emission may be connected with the center. 

Connection of V with 833 and 847 nm lines with long decay time in luminescence spectrum of topaz (Fig. 5.29e,f) is also possible (Gaft et al. 2003a). 

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 +. 

Figure 4.37a represents the time-resolved luminescence spectrum of a hydrozincite under 266 nm laser excitation. A relatively broad band is detected at 430 nm, which is responsible for the well-known blue hydrozindte luminescence. Its spectral position and decay time of approximately 700 ns are typical for Eu luminescence. However, the excitation spectrum of this band consists of one narrow band at 240 nm (Fig. 4.37b), which does not correspond to an Eu " excitation spectrum. Two bands usually characterize the latter with relatively small Stokes shifts of 30-50 nm caused by crystal field splitting of the 4/ 5d-levels. Moreover, the measured Eu concentrations in the hydrozincite samples under investigation are very low (less than 0.5 ppm) and they do not correlate with the intensity of the blue luminescence, i.e. the band at 430 nm. 

Fig, 5.66. Laser-induced time-resolved luminescence spectrum (a) and excitation spectrum (b) of radiation induced center in calcite... 

The luminescence spectrum of the Canada apatite contains the yellow band, which is similar to Mn + emission in the Ca(II) site (Fig. 5.71). Nevertheless, this band has short decay time, which is not suitable for strictly forbidden d-d transitions in Mn +. It dominates in the time-resolved spectrum with a delay of 10 ps and gate of 100 ps when the shorter-lived centers are quenched, while the longer-Hved ones are not detected. A change in the lifetime may be indicative of the energy transfer from Mn + by a radiationless mechanism. A condition necessary for this mechanism is coincidence or a close distance between energy level pairs of the ion sensitizer and the ion activator. Here, the process of luminescence is of an additive nature and a longer duration and greater quantum yield of the activator luminescence accompany a reduced... 

Fig. 5.71. a-f Unidentified emission center in apatite laser-induced time-resolved luminescence spectra of apatite, a Steady-state luminescence spectrum b Time-resolved spectrmn with narrow gate where yellow band with short decay time dominates c-d Time-resolved spectra after heating at 800 °C e-f Excitation bands of Mn and short-lived yellow band, correspondingly... 

In the first attempts to overcome the background problem using decay time, the variation of the fluorescence decay time as a function of wavelength across the entire emission profile for a variety of materials have been used (Measures 1985). For a variety of rocks and minerals, it was proved that this information represents a new kind of signature, the so called fluorescence decay spectrum, that possesses considerable discrimination power, being able to characterize the irradiated material with far superior precision than the normal luminescence spectrum (Fig. 7.2). 

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. 

Examples of the low temperature luminescence spectra are shown in Fig. 8.12. The luminescence intensity is highest in samples with the lowest defect density and so we concentrate on this material. The role of the defects is discussed in Section 8.4. The luminescence spectrum is featureless and broad, with a peak at 1.3-1.4 eV and a half width of 0.25-0.3 eV. It is generally accepted that the transition is between conduction and valence band tail states, with three main reasons for the assignment. First, the energy is in the correct range for the band tails, as the spectrum lies at the foot of the Urbach tail (Fig. 8.12(6)). Second, the luminescence intensity is highest when the defect density is lowest, so that the luminescence cannot be a transition to a defect. Third, the long recombination decay time indicates that the carriers are in localized rather than extended states (see Section 8.3.3). 

Cs2ZrCl6. A series of sharp transitions are observed that reflect the undistorted octahedral nature of these excited states. Excitation into these features produces the upconversion luminescence spectrum shown in Fig. 19 a. The 10 K excitation scan of this luminescence is compared to the absorption spectrum in Fig. 19b. The upconversion excitation scan closely follows the absorption profile over the full energy range. This observation leads to the conclusion that at 10 K the dominant mechanism for upconversion in 2.5% Re + Cs2ZrCl6 under these conditions is GSA/ETU. Time-dependent measurements confirm this conclusion (Fig. 19 a, inset), showing the characteristic delayed maximum and a 10 K decay constant (/Cdec = 1400 s ) approximately two times that of the excited... 

Commercial spectrometers, such as the Perkin-Elmer MPF-43A fluorescence spectrometer, that allow interlocking of excitation and emission monochromators lately have become available for utilizing this underexploited analytical technique. The synchronous luminescence technique reduces the complexity of the luminescence spectrum of a compound compared with a conventionally obtained luminescence spectrum. One can, therefore, better tackle the analysis of fairly complex mixtures without resorting to techniques that are expensive or excessively time consuming. 

A dynamics of nanocrystals formation has been also investigated. The luminescence spectra of colloidal solutions were registered during the reaction. Luminescence was excited by He-Cd laser with the wavelength of 325 nm. Fig. 1 shows the luminescence spectra of CeP04 Tb (15 mol.%) colloidal solution depending on the synthesis time. After 1 h of synthesis, the luminescence spectrum consists of the single intensive broad band with maximum at 370 nm, which corresponds to the luminescence of amorphous cerium phosphate particles. Only after 2 h of synthesis the narrow luminescence bands associated with the Af intrastate transitions of Tb were observed. The Tb ions are not... 

The absorption spectrum of [Ru(bpy)(phen)2] in acetonitrile shows a maxima at 448 nm (e 1.65 x 10 ) and 262 nm (e 9.17 x 10 ), which have been assigned to metal-to-ligand charge transfer and ir ir transitions, respectively." In addition shoulders at 430 and 284 nm are observed. The luminescence spectrum and emission life time in aqueous solution at 298 K have also been determined. Electrochemical studies estimate Eyn for the Ru +/Ru couple in acetonitrile at 1.30 V." The characteristic H NMR spectrum has also been recorded. The spectroscopic properties of [Ru(bpy)3] + have been summarized recently in this series. ... 

More recently (1965) Ryskin, Tkachuk and Tolstoi (30) measured the relaxation time t of a large number of platinocyanides and found t to be of the order of 10 to 10 sec. They also noted that the independence of the luminescent spectrum with regard to the exciting radiation shows that the redistribution of the electrons on the excited levels responsible... 

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