Light emission characteristics

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... 

When heavy atoms are introduced into the framework of a molecule, marked changes in the light emission characteristics occur. In particular, for complex molecules which contain metal ions from the second and third transition series, only a single emission from a set of thermally equilibrated excited levels is generally observed (J-7). This behavior is apparently associated with a spin-orbit coupling eflFect, and, indeed, it has been suggested that this effect is so large as to render spin labels inappropriate in second- and third-row metal complexes (8). 

The size of a quantum dot is important for the tunable light emission characteristic. A small... 

The size of a quantum dot is important for the tunable light emission characteristic. A small quantum dot, such as a colloidal semiconductor nanocrystal, can be as small as 2 to 10 nm [6]. A self-assembled quantum dot is typically between 10 and 50 nm in size [7]. A quantum dot defined by lithographically patterned gate electrodes or by etching on two-dimensional electron gases in semiconductor heterostructures can have lateral dimensions exceeding 100 nm [8]. 

The behavior of this Ru(II)-Cr(III) chromophore-Iuminophore complex (as well as of some related ones [69]) provides an example of how the properties of a luminophore can be improved by attachment to a suitable chromophoric component (spectral sensitization, antenna effect, avoidance of possible quartet photoprocesses). When very specific light absorption and light emission characteristics are required (e.g., in the design of luminescent labels for biochemical applications), the use of chromophore-Iuminophore systems may represent a convenient strategy. In particular this strategy permits separate optimization of absorption and emission properties, a possibility which is precluded in simple molecular species. 

Fig. 16-4 shows the current and light emission characteristics of one of the simple, early LEDs, consisting of ITO-glass/P(PV)/Ca. The effect of the metal electrode used on the efficiency is shown for the same basic device in Fig. 16-5. Detailed studies of the effect of the electron-injecting metal electrode, for example with poly(3-octyl thiophene) [492, 754], have shown that a change of just 0.9 eV in the metal work function (corresponding to a change from Au to Al) results in a change in the preferred current direction and a change in the LED rectification ratio of six orders of magnitude.

In Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), a gaseous, solid (as fine particles), or liquid (as an aerosol) sample is directed into the center of a gaseous plasma. The sample is vaporized, atomized, and partially ionized in the plasma. Atoms and ions are excited and emit light at characteristic wavelengths in the ultraviolet or visible region of the spectrum. The emission line intensities are proportional to the concentration of each element in the sample. A grating spectrometer is used for either simultaneous or sequential multielement analysis. The concentration of each element is determined from measured intensities via calibration with standards. 

Figure 16-39. Electrical characteristics of the 1TO/OPV5/AI devices U-OPV5 (A), Oocl-OPV5 (O). and Ooct-OPV5-CN" ( ). The arrows indicate the onset of light emission.

Fig. 5.4 Chemical mechanism of light emission in the bio- and chemiluminescence reactions of coelenterazine. The bottom row shows some of the fluorescence emitters of coelenteramide. The fluorescence characteristics of the dianion are unknown.

Molecular characteristics of luciferase. A molecule of the luciferase of G. polyedra comprises three homologous domains (Li et al., 1997 Li and Hastings, 1998). The full-length luciferase (135 kDa) and each of the individual domains are most active at pH 6.3, and they show very little activity at pH 8.0. Morishita et al. (2002) prepared a recombinant Pyrocystis lunula luciferase consisting of mainly the third domain. This recombinant enzyme catalyzed the light emission of luciferin (luminescence A.max 474 nm) and the enzyme was active at pH 8.0. The recombinant enzyme of the third domain of G. polyedra luciferase was crystallized and its X-ray structure was determined (Schultz et al., 2005). A -barrel pocket putatively for substrate binding and catalysis was identified in the structure, and... 

All of the compds exhibit a definite absorption peak in the UV region. These spectroscopic data are listed in Table 1. To fully correlate these light absorption data with the curves in Fig 1, consideration must be given to the emission characteristics of the pure scintillator. PPO in toluene (4g/5) has an emission range of 3400 to... 

The luminescence of an excited state generally decays spontaneously along one or more separate pathways light emission (fluorescence or phosphorescence) and non-radiative decay. The collective rate constant is designated k° (lifetime r°). The excited state may also react with another entity in the solution. Such a species is called a quencher, Q. Each quencher has a characteristic bimolecular rate constant kq. The scheme and rate law are... 

Room-temperature fluorescence (RTF) has been used to determine the emission characteristics of a wide variety of materials relative to the wavelengths of several Fraunhofer lines. Fraunhofer lines are bands of reduced intensity in the solar spectrum caused by the selective absorption of light by gaseous elements in the solar atmosphere. RTF studies have recently included the search for the causes of the luminescence of materials and a compilation of information that will lead to "luminescence signatures" for these materials. For this purpose, excitation-emission matrix (EEM) data are now being collected. 

The top-emitting OLED with a bilayer anode of Ag/CFX and an ultrathin Ag layer used in the upper semitransparent cathode forms an optical microcavity, which can tailor the spectral characteristics of the emitters therein by allowing maximum light emission near the resonance wavelengths of an organic microcavity [80,81], When the mode wavelength of the cavity is fixed at 550 nm, the thickness of the Ph-PPV layer is determined to be about 110 nm [81]. 

Figure 7.6 shows typcial current density-voltage-luminance (J-V-L) and emission characteristics of an OLED device. OLEDs have a similar electrical characteristic to that of a rectifying diode. In forward bias, the device starts with a small current at low voltages. In this region, charge carriers are injected into the device but little exciton formation, hence light... 

---