Emission efficiency

The light-emission characteristics of a white-light-emitting EL device with a doubly doped ZnS Pr,Ce,F phosphor layer have been described. It was observed that optimization of the co-doping of Ce enhances the emission characteristics compared to an EL device with a singly doped ZnS Pr,F layer.22 An electrical characterization of Ce-doped ZnS TbOF EL thin films has been reported Ce doping was seen to improve the radiative emission efficiency leading to improved performance of Ce co-doped film.23... 

Field emission displays are VFDs that use field emission cathodes as the electron source. The cathodes can be molybdenum microtips,33-35 carbon films,36,37 carbon nanotubes,38" 16 diamond tips,47 or other nanoscale-emitting materials.48 Niobium silicide applied as a protective layer on silicon tip field emission arrays has been claimed to improve the emission efficiency and stability.49 ZnO Zn is used in monochrome field emission device (FED) displays but its disadvantage is that it saturates at over 200 V.29... 

Fig. 8. Emission spectra at 78 K from hydrogenated Si+-implanted Si, from crystalline Si (c-Si), and from hydrogenated amorphous Si (a-Si H). Eg is the energy gap. The numbers labeling the peaks are the external emission efficiencies.

The same Suzuki methodology was used to synthesize a similar copolymer 446 [548], The polymer showed a solvent-dependent green-yellow emission (from 545 nm in THF to 565 nm in chloroform) as often observed for polar chromophores. The PL QE also varied with the solvent (from 11% in THF to 21% in decalin) but, in contrast to copolymer 445, no strong decrease in emission efficiency was observed in the solid state (4>p1 n= 13%) that could be attributed to the effects of substituents at the thiophene ring. LEDs based on 446 showed, for an ITO/PEDOT/446/Ca/Al architecture, a turn-on voltage of ca. 10 V with a maximum brightness of 340cd/m2 at 22 V and appreciable el = 0.14%. 

P.L. Burn, A.B. Holmes, A. Kraft, D.D.C. Bradley, A.R. Brown, R.H. Friend, and R.W. Cymer, Chemical tuning of electroluminescent copolymers to improve emission efficiency and allow patterning, Nature, 356 47-49, 1992. 

White PHOLEDs may become the most effective light source of the future due to their 100% internal emission efficiency, which raises the possibility to approach the upper limit of the maximum external power efficiency of 80 lm/W with CRI >80 [327]. Currently, the major challenge facing such white PHOLEDs are their lifetime and color stability under operating conditions. 

S Tokito, M Suzuki, and F Sato, Improvement of emission efficiency in polymer light-emitting devices based on phosphorescent polymers, Thin Solid Films, 445 353-357, 2003. 

FIGURE 9.14 (continued) (c) The effective light emission luminance (solid square, /.emission) and effective light emission efficiency (open square) versus effective current density of 4-a-Si H TFTs 200 dpi AM-PLED are shown. The evolution of luminance (solid circle, Z-pled) and light emission efficiency (open circle) versus effective current density of the red PLED are also shown, (d) Electroluminescent (EL) spectra and CIE color coordinates of 4-a-Si H TFTs 200 dpi AM-PLED (solid line) and PLED (dashed line) are shown. (From Hong, Y., Nahm, J.-Y., and Kanicki, J., Appl. Phys. Lett., 83, 3233, 2003. With permission.)... 

Sohn et al.27 used GAs to try to determine the composition of a high luminescence phosphor at 400 nm. Rather than relying on a theoretical model to assess the fitness of solid mixtures proposed by the GA, they synthesized each mixture and measured the emission efficiency experimentally. This is in... 

Seki, J., and T. Yamamoto, 1980. Amorphous interstellar grains wavelength dependence of far-infrared emission efficiency, Astrophys. Space Sci., 72, 79-86. 

From the integrated current passed through the ECL cell in the forward step, one can obtain the number of reactant species generated. Comparison of this value with the total number of photons produced (integrated absolute emission-time curve) provides information about the ECL emission efficiency ecl and the yields of the... 

The determination of the triplet-state yield when benzene vapor is irradiated depends not only on the emission yield of biacetyl as determined by Almy and Gillette32 but on the absolute emission efficiency of benzene itself. When all corrections are applied, the biacetyl method gives a triplet-state yield at incident wavelengths 2530-2590 A of about 0.63 with an uncertainty hard to estimate but perhaps 0.1. Below 2530 A the emission efficiency decreases, and by 2400 A the emission efficiency has fallen to zero. 

The advantages of flame photometry are reasonably good sensitivity, convenience, and versatility. For the alkali elements it is accepted as the standard method for water samples and can give good precision under carefully controlled conditions. The sensitivity for many elements (—i.e., zinc) is poor, and there can be severe matrix problems. Not only are there many examples of enhancement and suppression by other elements, but foreign constituents as they affect the viscosity, surface tension, and volatility of the samples can affect the emission efficiency (4, 11). 

This is the well known Stem-Volmer relationship which relates the number of photons absorbed per unit volume per second (/,) to the number emitted per unit volume per second (/f). The quantity 7f//a is the emission efficiency and is often given the symbol Q. 

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