Luminescence visible emission

The discriminatory emission properties between two-coordinate d ° gold(I) complexes and their respective three-coordinate counterparts have been demonstrated in the literature [6, 10-13]. As discussed in the later sections, Che and coworkers have rationalized that the extraordinarily large Stokes shift of the visible emission of [Au2(diphosphine)2] from the [5da 6pa] transition is due to the exciplex formation ofthe excited state with solvent or counterions [6]. Fackler [14—16] reported the photophysical properties of monomeric [AUL3] complexes, which show visible luminescence with large Stokes shifts (typically lOOOOcm ), suggesting significant excited-state distortion. Gray et al. [10] examined the spectroscopic properties of... 

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. 

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. 

By fluorescent decay, one refers to the measurement and analysis of the transient ultraviolet, infrared, or visible emissions of a luminescent material following or during excitation. Optical, electronic, nuclear, or X-ray radiations can be used to supply the required energy. 

Ceria only exhibits weak luminescence therefore, doping wifh rare earths such as Eu can enhance the visible emission required for imaging. Babu et al. reported the Eu + doped 10 nm ceria NPs s)mthesized by room temperature chemical precipitation and post annealing at 500 and 900 °C (Babu et al., 2008). A fraction of Ce exisfs in fhe ceria NPs, and if decreases after annealing. Emission intensity varies with the wavelength of excitation and observed transitions indicate the presence of Eu in different symmetry environments. 

A relatively new class of luminescent materials are the fi"-aluminas. Sodium alumina when doped with approximately 10 Cu+ cm has a visible emission in the green, which can be tuned from the blue to the red by the addition of codopants such as Ca+, Ba+, or Ag+. ... 

Figure 1 is photoluminescence spectrum of ZnO microtubes without annealing. The PL spectrum possesses a visible emission band. The visible emission centered at about 582 nm ranging from 400 nm to 660 nm is associated with oxygen vacancies. The broadening of the visible emission can be ascribed to abundant surface defects. A large quantity of defects and impurities on the surface of ZnO microtubes can provide new states which can contribute to visible luminescence centers and broaden the visible emission band. ... 

Luminescence, the emission of electromagnetic radiation in excess of that thermally generated, has been observed in several azides. The emission typically occurs in the ultraviolet, visible, or infrared regions of the electromagnetic spectrum. Some external stimulus is required prior to luminescent emission. The stimulus can take the form of photons, energetic particles, electric field, mechanical energy, or energy available from chemical reaction. 

X-ray phosphors can be defined as materials which absorb X rays and convert the absorbed energy efficiently into luminescence, in practice often ultraviolet or visible emission. In this paragraph we consider the phenomenon of X-ray absorption, and the principles of some important ways of X-ray imaging and the requirements which X-ray phosphors have to satisfy in order to be promising for potential application. 

Both fluorescence and phosphorescence are types of photoluminescence (often simply referred to as luminescence), the emission of radiant energy (usually visible radiation, but sometimes ultraviolet or infrared radiation) by a molecule, ion, or atom that has reached the excited state by absorbing radiant energy (usually, but not always, ultraviolet radiation) ... 

Fluorescent screen Different luminescent materials under exposure of ionizing radiation such as invisible alpha particles, electrons, UV light, etc., display visible emission... 

Concerning the luminescence of the lanthanides, the f f transitions are actually described by the spectroscopic levels of the ion, either down to the groimd state or down to an intermediate level. Usually, the visible emissions of the lanthanide ions have transitions that change the total spin number of the ion, i.e., the (2 5 + 1) multiplicity, whereas the NIR emissions do not change the spin. Since several lanthanides exhibit both mechanisms, the term litminescence is preferred over fluorescence or phosphorescence for the lanthanide ions. In this way, the common mistake of calling fluorescence all kind of emissions is avoided. Becatrse of their forbidden character, f-f transitions are slow and the lanthanide luminescence may take up to a few miUiseconds (jns = 10 s). 

In complexes (1-6), the outer two Schiff-base hgands display a curved bowl-like configuration, while the inner Schiff-base ligands are virtually planar. Intramolecular n-n stacking interactions between phenylene units are found in all these multidecker structures, which may further add to the stability of the complexes (Figures 1-6). The photophysical properties of complexes (16) have been studied in solution. Upon excitation of the hgand-centered absorption band, (1) and (3) show visible emission bands typical of the Tb + ion ( D4 - F transitions n = 6, 5, 4, and 3), (2) shows near infra-red (NIR) luminescence of Yb + ion ( Fs/2 F7/2... 

The active participation of Sq level is indirectly accredited by the simultaneous observation of UV and visible emission in cathodoluminescence and synchrotron excited spectra (Fig. 5.8) Excitation into the 4f5d and higher lying bands evidently decays to the Sq level located at 46,300 cm which exhibits luminescence in wide band-gap hosts due to radiative de-excitation to the lower lying levels of Pr. The So- F4 transition at 246 nm is especially strong in oxyapatite. In F-apatite only the line at 269 nm is present. It may be explained by the relatively long-waved absorption edge in fluorapatite, which is at about 300 nm (Morozov et al. 1970). 

It is well known that visible luminescence is observed even in some kinds of polysilanes. In methylnaphtylpolysilane, visible emission is observed from die excimer sites formed by the stacking of naphtyl sidechains. In mediylphenylpolysilane, the visible emission is due to a n interaction between the silicon backbone and phenyl sidechains. Silicon network polymers, however, exhibited no marked differences in photoluminescence spectra, regardless of their sidechains. This indicates that photoluminescence originates from the silicon backbone itself. 

Students then prepare three aqueous samples - one below the critical micelle concentration (or cmc, the concentration required for micelles to form), one above cmc, and one significantly above cmc. The addition of a fluorescent probe (with a visible emission that is sensitive to the polarity of its environment) presents students with a visible cue of the formation of micelles using a handheld ultraviolet lamp. At low surfactant concentration, the luminescent probe is in a polar environment (water), while above cmc it becomes trapped within the non-polar interior of the micelle. Comparison of the color and intensity of samples below and above cmc provides evidence for the notable difference of environment in the immediate vicinity of the probe (see Figure 2 b-c). The third sample becomes quite viscous, which provides evidence for the presence of elongated worm-like micelles that become entangled at high concentration (55). 

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