Laser-excited luminescence spectra

Fig. 9. Laser-excited luminescence spectra of a single crystal of KAu(CN)2 at temperatures of 8,140 and 295 K with excitation wavelength of 337 nm [11]...

Figure 25. Laser-excited luminescence in fossil fish teeth from phosphorite beds in the Senonian Mishash formation, Israel. (A) Uranyl emission at 77 K indicating uranyl aqueous complexes. (B) after annealing at 1000 K the uranyl complexes are dehydrated . (C) Same as in A but spectrum collected at 300 K. From these data it was concluded that the uranyl resides in organic material and not in the apatite structure. Modified after Gaft et al. (1996b).

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...

Under laser excitation, Eu (I) is especially prominent under Aex = 266 nm and it is the main form of Eu " in natural apatites. Extremely rare, 337 and 355 nm excitations lead to the appearance of the new Unes at 574,623,630 and 711 nm (Fig. 4. Id), which are similar to those received as a result of activation in air. Thus they are connected with Eu " " in the low symmetry Ca(II) site. Because of the lower symmetry its luminescence has a relatively short decay time and is more prominent in the spectrum with a narrower gate width. This center is especially strong at liquid nitrogen temperature where the prominent Dq- Fq line at 574 nm can bee seen, unhidden by Dy " luminescence. 

Figure 4.14c demonstrates time-resolved luminescence spectra of caldte, Franklin, NJ, under 266 nm laser excitation. A very intensive UV band at 312 nm with a short decay time of 120 ns is detected. It may not be connected with Ce emission, because its spectrum is situated at a substantially longer wavelength near 400 nm (Fig. 4.14e). The excitation spectrum of the band at 312 nm consists of one band at 240 nm (Gaft et al. 2003a).

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... 

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... 

Under short-waved UV lamp excitation (254 nm) visually observed luminescence of calcite is violet-blue with very long phosphorescence time of several seconds. Under long-waved UV lamp excitation (365 nm) calcite exhibits visually the same violet-blue luminescence as under 254 nm excitation, but long phosphorescence is not detected. Under short laser excitations, such as 266 and 355 nm, at 300 K calcite demonstrates intensive UV-violet emission band peaking at 415 nm with half-width of 55 nm (Fig. 5.76a). Excitation spectrum of this band is composed of short waved tail in the spectral range less... 

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. 

Figure 2. Luminescence spectra of CeoFWS excited by different laser wavelengths. Raman spectrum of water is subtracted.

The photoluminescent behavior of a complex of the type Zn(diimine)(dtsq), where diimine = 2,2 -biquinoline, phen (44), or 4,7-diphenyl-2,9-dimethyl-phen (batho) and dtsq = dithiosquarate, have been reported by Gronlund et al (135). The phen and batho complexes display broad, featureless luminescence spectra in the solid state at room temperature. Upon cooling to 77 K, the emission spectrum of Zn(batho)(dtsq) resolves into three sharp peaks overlapping the broad emission feature these sharp peaks are assigned to a diimine localized ji-ji emission. The Zn(diimine)(dithiolate) solids degrade upon UV laser excitation, which has inhibited accurate lifetime measurements. 

Figure 1. Luminescence spectrum (excited at 277 nm) and TEM image of Gd20j Tb nanoparticles produced by laser ablation.

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... 

Luminescent standards have been established for use in calibrating fluorescence spectrometers and have been suggested for Raman spectroscopy in the past (18). The standard is a luminescent material, usually a solid or liquid, that emits a broad reproducible luminescence spectrum when excited by a laser. Once the standard is calibrated for a particular laser wavelength, its emission spectrum is known, and it can provide the real standard output , d)i(AF) depicted in Figure 10.8. In practice, a spectrum of the standard is acquired with the same conditions as an unknown then the unknown spectrum is corrected for instrument response function using the known standard... 

Fig. 6 Delayed luminescence spectrum of a PF2/6 film taken at 20 K with 30 ms delay after excitation and 30 ms detection window. Excitation was provided at 355 nm with 170 ps pulse width using a Nd YAG laser...

Similar behavior has been observed in CdSe clusters [60], Using laser excitation near the red edge of the absorption band, sharp luminescence with well-defined vibronic structures can be observed. The decay kinetics shows two components—a temperature-insensitive 100-ps component and a microsecond, temperature-sensitive component. The luminescence spectrum develops a 70-cm-1 red shift as the fast component decays. The three-level thermal equilibration model again has to be invoked to explain these kinetic data. Based on the polarization measurement, the authors suggest that it is the hole, instead of the electron, that is shallowly trapped. The trap depth is estimated to be 9 meV. The authors further propose that strong resonant mixing exists between the internal MOs and surface MOs. 

Fig. 8. Luminescence spectrum and spectral dependence of (A///)esk at resonances of the Dj (A/ < 0) and A (A/ > 0) centers at 2 K under excitation by argon ion laser light of 25 mW in a-Si H No. 541 T, = 120°C). Each value in the ordinate is plotted in arbitrary units. [From Sano et al. (1982b).]...

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