Fluorescence amorphous materials

TEM offers two methods of specimen observation, diffraction mode and image mode. In diffraction mode, an electron diffraction pattern is obtained on the fluorescent screen, originating from the sample area illuminated by the electron beam. The diffraction pattern is entirely equivalent to an X-ray diffraction pattern a single crystal will produce a spot pattern on the screen, a polycrystal will produce a powder or ring pattern (assuming the illuminated area includes a sufficient quantity of crystallites), and a glassy or amorphous material will produce a series of diffuse halos. 

Alternatively, can be calculated from the sum of the products of the theoretical mass absorption coefficient (jij ) of each element (or phase) and the weight fractions (Wj) of all n elements (or phases) in the sample. Elemental composition may be determined, for example, by X-ray fluorescence (XRF) measurement and use of this is more accurate than the use of phase composition as it takes into account any amorphous material not represented by peaks in the diffraction pattern but which still contribute to p . ... 

Finally, the background in a powder pattern indicates whether or not an amorphous material is present in the sample. A high background relative to the peaks is usually caused cither by a large amount of amorphous material (e.g. unreacted gel) or by X-ray fluorescence. The latter is observed, for example, if an Fe-containing sample is irradiated with CuKa radiation. It can be avoided by changing the wavelength (e.g. to CoKa radiation). 

By freeze-fracture analysis, this amorphous material was found to be associated with the openings of plasma membrane vesicles. The amorphous material did not stain with PAS or Alcian blue or fluorescent lectins and was thereby thought unlikely to be mucin or other glycoprotein (Williams and Elias, 1981). 

Table 1. Common materials used in quenched-fluorescence oxygen sensing (Ru(dpp)3(C104)2 tris(diphenylphenantroline) ruthenium(II) perchlorate PtOEPK platinum(II)-octaethyl-porphine-ketone PtPFPP platinum(II)-tetrakis(pentafluorophenyl)porphine PS.poly(styrene), PSu poly(sulfone) PSB poly(styrene-butadiene) block co-polymer PVC polyvinylchloride) APET amorphous poly(ethyleneterephthalate) PE poly(ethylene).

Bis(dimesitylboryl)-2,2 -bithiophene (BMB-2T, 242) forms a stable amorphous glass and emits pure blue color with a high fluorescence QE of 86% in THF solution [270]. However, an OLED with ITO/m-MTDATA/TPD/BMB-2T/Mg Ag emits with a broad emission due to an exciplex with TPD. The exciplex can be prevented by insertion of a thin layer of 1,3,5-tris(biphenyl-4-yl)benzene (TBB) between TPD and BMB-2T, leading to a pure blue emission. It seems that the boron complex or boron-containing compounds easily form an exciplex with common HTMs. Other similar blue emitter materials also demonstrate such behavior. 

Stilbeneamines. The functionalization of stilbenes with arylamino groups leads to materials that emit in the green-to-yellow spectral region. For example, 9,10-bis(4-(7V,/V-diphenylamino)styryl-anthracene (BSA, 21) absorbs at429nm and emits at 585 nm [141]. Compound 21 and other derivatives of bistyrylanthra-cene have been successfully applied in yellow emitting OLEDs [64]. Tetra(tri-phenylamino)ethylene (TTPAE, 20) emits at 539 nm [109]. The latter compound exhibits a large quantum yield of 25% in the amorphous film, but does not show fluorescence in solution. 

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