Photoluminescent efficiency

Metal-centered emission is found in several rare-earth complexes, for example europium diketone chelates [29]. These compounds emit relatively narrow spectra associated with the d-f transitions of the metal ion. Relatively few comprehensive studies of this class have been carried out to date, but the available evidence [30] seems to indicate that the photoluminescent efficiencies are somewhat lower than the ligand-centered emitters. 

J. Pei, W.-L. Yu, J. Ni, Y.-H. Lai, W. Huang, and A.J. Heeger, Thiophene-based conjugated polymers for light-emitting diodes effect of aryl groups on photoluminescence efficiency and redox behavior, Macromolecules, 34 7241-7248, 2001. 

M.R. Andersson, M. Berggren, T. Olinga, T. Hjertberg, O. Inganas, and O. Wennerstrom, Improved photoluminescence efficiency of films from conjugated polymers, Synth. Met., 85 1383-1384, 1997. 

L. Antolini, E. Tadesco, G. Barbarella, L. Favaretto, G. Sotgiu, M. Zambianchi, D. Casarini, G. Gigli, and R. Cingolani, Molecular packing and photoluminescence efficiency in odd-membered oligothiophene S,5-dioxides, J. Am. Chem. Soc., 122 9006-9013, 2000. 

D.Z. Garbuzov, Y. Bulovic, P.E. Burrows, and S.R. Forrest, Photoluminescence efficiency and absorption of aluminum-tris-quinolate (Alq3) thin films, Chem. Phys. Lett., 249 433M-37 (1996). 

The absorption spectrum of 468 in solution is characterized by the presence of an intense and structured band near 300 nm and by a broad and much weaker band around 350 nm, whereas the corresponding spectrum of 469 shows the presence of an intense featureless band at 364 nm. Dithieno derivative 469 is characterized by high emission efficiency in solution, more than two orders of magnitude greater than that of oligomers containing the thienyl-S,S-dioxide moiety. On the contrary, the photoluminescence efficiency of dithieno derivative 468 in solution is almost 20 times lower than that of 469. 

Whereas in solution the photoluminescence efficiency (Of) of poly(3-alkylthiophenes) (PATs) is 3(Mf)%, it drastically drops to 1-4% and lower in the solid state due to the increased contribution of nonradiative decay via interchain interactions and ISC caused by the heavy-atom effect of sulfur (97MM4608). Optoelectronic devices of this type of compounds have been studied (98SCI(280)1741 06SM(156)1241). Fibers of poly(3-hex-ylthiophene) for photovoltaic applications have been described (07MI1377). Poly(3-octylthiophene) showed a TTA band at 800 nm (96JPC15309). The photophysical properties of some alkyl and aryl polythiophenes have been studied (03JCP(118)1550). The absorption maximum of poly(3-octylthiophene) is at 438 nm, while the fluorescence was... 

One of the advantages of lanthanide-doped semiconductor nanocrystals is that lanthanide luminescence can be efficiently sensitized by exciton recombination in the nanocrystals. The photoluminescence efficiency of Er3+ in Si nanocrystals in Si02 increases by more than five... 

A single-step preparation of a new class of soluble co- and terpoly(arylene-oxadia-zole) polymers containing at least 20 repeat units have been prepared by the condensation of aromatic dicarboxylic acids with hydrazine hydro-chloride. Photoluminescence efficiencies of 50% were reported. Targeted applications include electroluminescent devices, photovoltaics, and diodes. 

TABLE 1. Photoluminescence efficiencies for selected experimental agents activated using a UV lamp at 365 nm. 

To be a good emitting material for use in OLEDs, firstly the lanthanide complex must have high photoluminescent efficiency, which is one of the essentials for excellent electroluminescence devices. As noted above, the external quantum efficiency hext of an OLED can be expressed as hext = hr other conditions are kept unchanged, the higher the photoluminescent efficiency, the better the electroluminescence performance. 

Similar to the europium complexes, the terbium complexes used as good emitters in OLEDs also need to have high photoluminescent efficiencies, good carrier transporting properties, and sufficiently good thermal stability for small molecule materials to form a film by thermal evaporation in vacuum. 

The irans-cis isomerization of 2-C4Hg proceeds catalytically on the ZnS catalyst under UV irradiation (245). The initial rate of this photocatalytic isomerization on preground ZnS was found to be relatively low, but it increased markedly when the grinding time increased. The effect of the grinding of the catalyst on the efficiency of photocatalytic isomerization was the opposite of the effect on the photoluminescence efficiency of the catalyst. 

Another factor which determines the efficiency of LEDs is the photoluminescence (PL) efficiency, i.e. the fraction of photoexcited states which recombine radiatively. Since the radiative lifetime of most conjugated polymers is less than 1 ns and there are relatively few non-radiative channels for relaxation, the PL efficiency can be quite high. Many conjugated polymers have photoluminescence efficiencies higher than 60%. A subject of substantial debate is whether or not the electroluminescence (EL) efficiency can be as high as the photoluminescence (PL) efficiency. As summarized in Section IVB, EL efficiency as high as 50% of the PL efficiency has been demonstrated [158]. 

These observations and one further criterion start to define quantum dot systems. The second major possibility is the coating of the central particle with a second material e.g. CdS or ZnS on top of CdSe. When a wider band gap material is coated onto the outside of a narrow band gap material the confinement on the core is enhanced, leading to enhanced optical properties, especially photoluminescence efficiencies. 

Copolymerization of various substituted PPV monomer units has been used to tune the electronic properties. In particular, the introduction of nonconjugated units into the polymer chain has been found to produce enhanced photoluminescence efficiencies by preventing diffusion of excitons along the chains to defect sites.33,34... 

FIGURE 10.40. The PFO fluorescence, PtOEP phosphorescence, and total photoluminescence efficiencies as a function of PtOEP concentration. The excitation source was the 354-nm line of a HeCd laser. (From Ref. 72.)... 

Polyfluorene with on-chain ruthenium complex (polymer 49) has been synthesized by Suzuki polycondensation [77]. The photoluminescence of the copolymer was slightly blue-shifted as the concentration of dipyridy-lamine increased. The introduction of dipyridylamine and the ruthenium complex into the polymer significantly improved the photoluminescence efficiency. 

Absolute photoluminescence efficiency measurements in thin solid films are quite difficult, since light-trapping, waveguiding effects and, possibly, distributions in tlie emission dipole moments of individual chromophores modify the angular distribution of the emission. De Mello et al. [126] have described an im-... 

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