Luminescence, photo

Size, shape, and density The shielding effects of dendritic shells can likewise be caused by steric factors. Thus, the access of foreign molecules to the central functional unit can be hindered or prevented according to size and density of the dendritic shell. Sometimes, even a certain size selectivity is observed. These effects are especially interesting for electrochemically, catalytically active, redox-and photo-active functional units, since interactions with foreign molecules, such as oxygen quenching of the luminescence (photo-active units) or the access of substrates (catalytically active units) can be influenced.14 11 17,221... 

In a recent study. Ford and coworkers reported the synthesis of 19 (Scheme 11.5), a luminescent photo-CORM (CO releasing molecule) based on 1, and easily incorporated in celk [67]. In this molecule the presence of the phosphine ligand increases its water solubility and makes the axial CO labile. Thus, upon irradiation, 19 released a CO molecule and was converted in its solvated (aqua) complex 20. Both molecules are strongly limiinescent, but notably their emission bands are centered at different wavelengths (515 and 585 nm, respectively). Consequently, accumulation of 19 in PPC-1 hiunan prostatic carcinoma cells (at a low concentration of incubation of 50 pM) followed by confocal microscopy is first associated with cells colored in blue (associated with the fluorescence of 19), and then release of CO upon irradiation led to green colored cells (associated with the fluorescence of 20) (Figure 11.7). 

Fig. 16.21 Room temperature upconversion emission spectra of a NaYF4 Yb/Er (18/2 mol%), b NaYF4 Yb/Tm (20/0.2 mol%), c NaYF4 Yb/Er (25-60/2 mol%), and d NaYF4 Yb/Tm/Er (20/0.2/0.2-1.5 mol%) particles in ethanol solutions (10 mM). The spectra in (c) and (d) were normalized to Er 650-nm and Tm 480-nm emissions, respectively. Compiled luminescent photos showing corresponding colloidal solutions of e NaYF4 Yb/Tm (20/0.2 mol%), f-j NaYF4 Yb/Tm/Er (20/0.2/0.2-1.5 mol%), and k-n NaYF4 Yb/Er (18-60/2 mol%). The samples were excited at 980 nm with a 600 mW diode laser. The photographs were taken with exposure times of 3.2 s for e-l and 10 s for m and n Reprinted from Ref. [52], with permission from Springer Science + Business Media...

The layer width is taken from the relation d > 1,5 dg, where dg - thickness of a gas discharge gap. The employment of a resistive layer instead of electrode profiling can significantly simplify the device manufacture. The UV radiation is efficiently converted into a visible one by a number of photo-luminophors, e.g. Zn2Si04 Mn. For stroboscopic registration of fast-proceeding processes the luminophors with short period of luminescence are used, e.g anthracene etc. 

Leuchtelektron, n. emitting electron, optical electron photo-electron, leuchten, v.t. give light, shine, glow, luminesce. 

MEH-PPV and P3MBET, were used. As a measure of the efficiency of the photo-induced charge transfer, the degree of luminescence quenching and the ratio of the charged photoexcitation bands to the neutral photoexcitation bands were taken. These two numbers are plotted in Figure 15-15 versus the electrochemical reduction potential. A maximum in the photoinduced electron transfer was determined for Cbo. 

Nanoparticles of Mn and Pr-doped ZnS and CdS-ZnS were synthesized by wrt chemical method and inverse micelle method. Physical and fluorescent properties wra cbaractmzed by X-ray diffraction (XRD) and photoluminescence (PL). ZnS nanopatlicles aniKaled optically in air shows higher PL intensity than in vacuum. PL intensity of Mn and Pr-doped ZnS nanoparticles was enhanced by the photo-oxidation and the diffusion of luminescent ion. The prepared CdS nanoparticles show cubic or hexagonal phase, depending on synthesis conditions. Core-shell nanoparticles rahanced PL intensity by passivation. The interfacial state between CdS core and shell material was unchan d by different surface treatment. 

Undoped, Mn, and Pr-doped ZnS namopartides synthesized by wet chemiral mdhod were optically annealed in air or vacuum. PL emission inoeas with annulling time. This increase is attributed to the photo-oxidation, enhancanent in the crystal quality, and diffiision of the luminescent ions. PL intensity of nanoparticles annealed in air increased more significantly due to the photo-oxidation compared with the nanoparticles annealed in vacuum. Mn and Pr-codoped ZnS nanoparticles emitted white light due to the effects of dopants. The optical annealing enhanced the emission intensity. 

PBE dendrons bearing a focal bipyridine moiety have been demonstrated to coordinate to Ru + cations, exhibiting luminescence from the metal cation core by the excitation of the dendron subunits [28-30]. The terminal peripheral unit was examined (e.g., phenyl, naphthyl, 4-f-butylphenyl) to control the luminescence. The Ru +-cored dendrimer complexes are thought to be photo/redox-active, and photophysical properties, electrochemical behavior, and excited-state electron-transfer reactions are reported. 

Fluorescent chemical sensors occupy nowadays a prominent place among the optical devices due to its superb sensitivity (just a single photon sometimes suffices for quantifying luminescence compared to detecting the intensity difference between two beams of light in absorption techniques), combined with the required selectivity that photo- or chemi-luminescence impart to the electronic excitation. This is due to the fact that the excitation and emission wavelengths can be selected from those of the absorption and luminescence bands of the luminophore molecule in addition, the emission kinetics and anisotropy features of the latter add specificity to luminescent measurements8 10. 

Ratiometric luminescent probes make a smart use of the excitation wavelength effect on the emission intensity for extended optosensor performance. For example, the fluorescence from 8-hydroxy-l,3,5-pyrenetrisulfonate (HPTS) and other pH-sensitive dyes in water comes only from its (photo)excited basic form, but the absorption spectra of HPTS and PTS (pAa 7.3) differ considerably (Figure 3). 

H.-Z. Tang, M. Fujiki, Z.-B. Zhang, K. Torimitsu, and M. Motonaga, Nearly pure blue photo-luminescent poly(2,7-[9- 3,5-bis[3,5-bis(benzyloxy)benzyloxy]benzyl] -9-(3,6-dioxaoctyl)]fluorene in film, Chem. Commun. 2426-2427, 2001. 

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