Liquid-nitrogen temperature emission spectra

Figure 2.6 Comparison of room-temperature versus liquid-nitrogen temperature emission spectra for [(CsMes)2Yb(2,2 -bipyridine)t in CH2CI2 solution illustrating the substantial improvement in band resolution at cryogenic temperature. These vibronically resolved emission bands for the Yb ion arise from transitions between the Fj/2 excited state and the ground state manifolds. The excitation in both spectra occurred at 440 nm from a continuous wave Xe arc lamp. Ryan E. Da Re and David E. Morris, Los Alamos National Laboratory...

The nature of the quenching mechanism can be easily confirmed by recording the emission spectrum in a frozen solution (EtOH/MeOH mixture (9 1) at liquid nitrogen temperature). Under these conditions, the relative decrease in fluorescence intensity expressed as I /Iq is equal to 0.82, while at room temperature it is 0.23. Such a reduction in quenching efficiency in a frozen solution is characteristic of an electron transfer mechanism. In fact, immobilization of the solvent molecules in a frozen matrix prevents the reorganization of solvent molecules sur-... 

CsI(Tl). CsI(Tl) has a higher density (4.51 X 10 kg/m ) and higher atomic number than Nal therefore its efficiency for gamma detection is higher. The light-conversion efficiency of CsI(Tl) is about 45 percent of that for NaKTl) at room temperature. At liquid nitrogen temperatures (77K), pure Csl has a light output equal to that of Nal(Tl) at room temperature and a decay constant equal to 10 s. The emission spectrum of CsI(Tl) extends from 420 to about 600 nm. 

Figure 4. Photoluminescence emission spectrum of octaphenylcyclotetrasiloxane solid, at liquid nitrogen temperature. Excitation wavelength 320 nm, spectral bandwidth ca. 8 nm.

TSL is observable in most dielectrics in polymers the sample is commonly irradiated at liquid nitrogen temperature and heated to room temperature at a rate of approximately 3" C/min. TSL emission in many commercial polymers is negligible above room temperature and the information, which can be extracted from a single TSL measurement on the molecular environment of the trapped electrons, is not as precise as from ESR. The TSL spectrum of a polymer may contain both fluorescent and phosphorescent components. TSL provides information about ageing processes and can be used as a method for early recognition of damage in polymers. Fleming [488] has reviewed thermally stimulated luminescence (TSL) for the analysis of polymers. 

Emission Mossbauer spectra of dried cells of Azospirillum brasilense (strain Sp245) that were incubated as live cells with CoCl2 for 2 min (a) and 60 min (b) at ambient temperature, then rapidly frozen in liquid nitrogen and freeze-dried prior to EMS measurements (spectra measured at 7=80 K see also Table 17.1). The positions of spectral components (quadrupole doublets) composing the whole spectrum (solid envelope), obtained by fitting the experimental data (points), are shown above the spectra with square brackets the same for other figures with emission spectra. (Adapted from Ref. 27.)... 

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