Blue peak emission

On the basis of the experimental data presented above, one cjin exclude on the onset several models for the "blue peak" emission. Firstly, spin-flip collision induced population inversion on the Di transition is not involved - due to both the off-resonant character of the emission and its independence on the buffer gas pressure. Similarly, pressure induced extra resonances are rejected. Stimulated electronic Raman and three photon scattering effects, both by a two or three level system, are dependent on the laser detuning and neither their frequencies are to the blue in the vicinity of the Di line (figure 2) thus, these processes are also excluded. 

We propose to explain the "blue peak" emission in terms of laser photon splitting into two photons, as shown schematically in Fig. 3. The laser creates a virtual level in the vicinity of the 3 P3/2 level. Subsequently two photons, quasiresonant with the P3/2" Pl/2 1/2 "... 

The precise control of ROMP methodology has been exploited by Schrock and co-workers in the polymerization of a norbomene monomer functionalized with a distyrylbenzene side-chain 70 [1051. When calcium is used as a cathode, an internal device efficiency of 0.3% is observed and the peak emission is in the blue (475 nm). 

Introduction of electron-accepting hi thieno[3,2-6 2, 3 -e]pyri dine units resulted in copolymer 308 with ca. 0.5 V lower reduction potential compared to the parent homopolymer PFO 195 [398]. Upon excitation at 420 nm (A ax =415 nm), copolymer 308 exhibited blue-green emission with two peaks at 481 and 536 nm. Preliminary EL studies of an ITO/PEDOT/308/A1 device showed two peaks positioned as in the PL spectra. The PLED exhibited low turn-on voltage ( 4 V) but at higher voltages of 6-9 V, a slight increase in the green component was observed (Chart 2.83). 

Recently, Chen s group reported a deep blue OLED based on an asymmetric mono(styryl) amine derivative DB1 (192) as shown in Scheme 3.59. PL spectra of this deep blue dopant in toluene solution showed a peak emission of 438 nm, which is about 20 nm hypsochromic shift compared with DSA-amine symmetric dopant, due to the shorter chromophoric conjugated length of the mono(styryl) amine. OLED device based on this blue dopant achieved a very high efficiency of 5.4 cd/A, with CIE coordinates of (0.14, 0.13) [234]. 

Bis(2-methyl-8-quinolinolato)aluminum hydroxide with only two quinolate ligands emits blue color with the maximum peak emission at 485 nm and FWHM of 80 nm [265], Devices fabricated with a structure of ITO/CuPc/NPD/AlMq2OH/LiF/Al give a maximum brightness of 14,000 cd/m2 at 480 mA/cm2. 

Replacing the metal Al by a boron atom as the metal chelate center, Tao et al. reported lithium tetra-(2-methyl-8-hydroxy-quinolinato) boron (LiB(qm)4, 240) (Scheme 3.73) quantitatively prepared by reaction of lithium borohydride (LiBH4) with four equivalents of 2-methyl-8-hydroxy-quinoline in ethanol at room temperature [266]. LiB(qm)4 is a pure blue emitter with a maximum peak emission at 470 nm with FWHM of 75 nm. Devices of... 

LEDs have already found a number of applications that demonstrate potential with respect to fluorescence measurements requiring routine operation, low cost, or compact implementations. A 50 mW LED (GaP) with a peak emission at 565 nm has been used in conjunction with HPLC separation and methylene blue fluorescence to detect... 

New absorption shoulders appear strongly at 250 and 345 nm. Given this evidence of ground-state interaction, the fluorescence band of the noneclipsed naphthalenophanes should be red-shifted below the peak emission of the dimethylnaphthalene solution excimer. In fact, the emission of chiral [2.2](2,6) naphthalenophane is blue-shifted 900 cm 1, and the emissions of the onh -[2.2](l,4), onfi-[3.3](l,4), and chiral [2.2](1,5)... 

Enstatite The first extensive observations of CL in meteorites were for enstatite (MgSiC>3) probably because it shows particularly brilliant CL colors and it is the major mineral in the enstatite achondrites. The visual CL is commonly described as blue, red or less commonly purple and the early spectra, mainly from powdered samples and using proton irradiation, clearly showed the presence of a blue and red emission (4-6). These emissions were confirmed using electron irradiation and spectra showed a blue peak near 400-420nm... 

To obtain a quantitative measure of the CL intensity of individual CL emissions, an optical multichannel analyzer was coupled to the optical system of an electron microprobe allowing simultaneous collection of CL spectra and minor element data from a single point (Steele, I.M. Meteoritics. submitted). For CL spectra obtained with a 15 kV focused beam, enstatite from both enstatite chondrites and achondrites showed three distinct peaks (Fig.l) centered at about 742, 664, and 483nm. To allow assignment of these peaks, spectra from synthetic Mn and Cr doped enstatite are shown in Fig. 2 and the emissions from these two samples closely match the two red peaks of meteoritic enstatite neither synthetic sample shows a blue peak. The peak positions of Cr and Mn are not constant for different meteoritic enstatites and are not the same as for the Cr and Mn doped standards. The variation is about 20nm... 

The two emission spectra can be compared in several ways. The lifetime of the "red" site emission is not represented by a single exponential decay and may be characterized by a triple exponential decay of T = 2.1 msec, 3.93 msec, and 6.3 msec. Blue site emission has a single 2.1 msec decay time. The peak shapes show in all... 

HOMO-LUMO gap of CN-PPV XIII is about 2.1 eV (590 nm) and two-layer electroluminescent devices made of ITO/PPV (as a hole transporting layer)/CN-PPV (as emitter)/Al or Ca, exhibit a red electroluminescence with a peak at 710 nm and a i7ext) of about 1 % [31]. The same two-layer configuration devices based on MEH-CN-PPV XIV exhibit a red-orange electroluminescence peaking at ca. 600 nm, a rjext = 2.5%, a luminous effiency of 2.5 lm/W, and a luminance of 1000 cd/m2 at 6 V [166,189]. The blue-shifted emission of MEH-CN-PPV in comparison with that of CN-PPV has been ascribed to a steric effect of the branched ethylhexyl side-chain, which induced a slight twisting of the polymer backbone. 

Contradictory results have been published on the photoluminescence of porous InP. Some authors reported blue-shifted photoluminescence peaks lying above the band gap energy interpreted in terms of quantum confinement [230]. Hamamatsu and coworkers reported that contrary to expectation of blue-shifted emission caused by quantum confinement at pore walls, porous (001) InP samples exhibited an intense red-shifted photoluminescence peak [231]. This was explained by the formation of a set of well-defined new surface state levels on anodized pore wall surfaces. 

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