Photoluminescence absorption spectra

Figure 9-12. Absorption (Abs), photoluminescence excitation spectrum (PLCX), pholo-lumincscence (PL), and electroluminescence (EL) emission of mLPPP.

The Cu ions have a weak absorption spectrum that partially overlaps with the emission band of Cu, resulting in resonant energy transfer. In fact the time course of oxygen chemisorption could be followed by monitoring the Cu1 photoluminescence quantum efficiency with the time of exposure of Cu Y to oxygen. 

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. 

Time-resolved photoluminescence was also used to show that the spatial separation of the electron and hole wavefunctions due to the piezoelectric fields in GalnN/GaN QWs leads to a dramatic reduction in oscillator strength, particularly for thick quantum wells [6]. Due to the reduced oscillator strength for the lowest energy state, the optical absorption spectrum of the quantum wells is expected to be dominated by highly excited states close to the strained bulk bandgap. 

The UV-visible absorption spectrum of the CdS nanotubes given in Fig. 2a shows a blue-shift in the excitonic absorption band to 460 nm. The blue-shift from the bulk value of 515 nm [12] is due to quantum confinement effects in the CdS nanotubes, the inner diameter of the nanotubes being less than the Bohr-exciton diameter of CdS (6 nm). Xiong et al. [13] have reported an absorption band at 459 nm for CdS nanotubes with an inner diameter 5 nm prepared by an in situ micelle-template-interface reaction. An absorption maximum around 450 nm has been reported in nanoparticles and hollow spheres of CdS [12,14], In Fig. 2b, we show the photoluminescence (PL) spectrum of the CdS nanotubes prepared by us, revealing a band centered at 610 nm. This band is due to charge carriers trapped at surface defects of the nanotubes [15,16],... 

The electronic absorption spectrum of the CuS nanotubes given in Fig. 5a shows the characteristic broad band of CuS in the near IR region, peaking at 1200 nm. The band is attributed to an electron-acceptor state lying within the band gap [17]. A similar broad band has been reported for CuS nanocrystals [27], The photoluminescence spectrum of CuS nanostructures given in Fig. 5b shows a broad band peaking at 560 nm with a shoulder at 480 nm. Bulk CuS is reported to show a broad band centered at 560 nm with a shoulder at 587 nm [17], The absence of any appreciable blue-shift of the emission bands of the CuS nanostructures prepared by us might be due to the formation of chains of nanorods by self-assembly. 

Figure 26 Emission spectra (PL, EL) in PC at room temperature of 40 wt% TPD donor solution with a 40 wt% of PBD acceptor added. The photoluminescence (PL) spectrum excited at 360 nm, the electroluminescence (EL) spectra (I, II) originate from the recombination radiation in a 60 nm thick film, taken at two different voltages. Absorption (Abs) and PL spectra (excitation at 360 nm) of (75wt% TPD 25wt% PC) and (75wt% PBD 25wt% PC) spin-cast films are given for comparison. Molecular structures of the compounds used are given in the upper part of the figure TPD [N,Nf-diphenyl-A v/V/-bis(3-methylphenyl)-l,l -biphenyl-4,4 diamine PBD [2-(4-biphenyl)-5-(4- er .-butylphenyl)l,3,4-oxadiazole PC[bisphe-nol-A-polycarbonate]. Adapted from Ref. 112.

A few mononuclear Au compounds have been found to photoluminesce in the sohd state but not in solution. The lowest energy band in the absorption spectrum of [Au2(/r-dmpm)2], which is reported to be luminescent in the solid state, has been assigned by using circular dichroism (CD) spectra to the transition cr(Pz) (d ). However, the compound [Au2(/r-dcpe)3](PF6)2, which has no An An contact, emits in the sohd state as weh as in acetonitrile solution (Xmax = 508nm, t = 21.5(5) p,s), indicating that An L bonding is also a factor to be considered in Au photophysics. ... 

It has been observed that the SWNTs suspended in a micellar solution exhibit a well-defined optical spectrum and show a bright photoluminescence in the near infrared region (Figme 22). The individual SWNT suspended in air at room temperature also shows a bright photoluminescence. The emission spectrum of the semiconducting SWNTs correlates well with the absorption spectrum in a micellar solution. The intensity of emission decreases dramatically when the isolated nanotubes start aggregating in a destabilized micellar solution. The decrease in the emission is attributed to the quenching of electrons by the metallic nanotubes when... 

The effective masses of electrons and holes are estimated by parabolic approximation a large curvature corresponds to a small effective mass and a small curvature corresponds to a large mass. With this band concept, light absorption and luminescence are interpreted as follows Light is absorbed by the transition from valence band to conduction band. Therefore, the broadening of the absorption spectrum originates basically from the one dimensionality of the joint density of states, which is described by (E - g) . Excited electrons and holes relax to the bottom of the bands and then recombine radiatively. Therefore, the photoluminescence of the spectrum is very sharp. The energy difference between two peaks is called the Stokes shift. 

On the other hand, in the excitation spectrum, the emission intensity 4, at the monitored emission band, is plotted as a function of the wavelength A of the excitation light, w hich varies as the extinction coefficient of the absorbing molecules. Therefore, the excitation spectrum exhibits the same spectral appearance as that of the absorption spectrum. The advantage of measuring the excitation spectrum in addition to the emission spectrum is the greater sensitivity even for low concentrations of photoluminescent material compared to standard absorption measurements. 

Figure 19 shows the typical photoluminescencc spectrum of the anchored vanadium oxide catalyst prepared by photo-CVD methods (a), its corresponding excitation spectrum (b), and the UV absorption spectrum of the catalyst (c) (56,115,116). These absorption and photoluminescence spectra (phosphorescence) are attributed to the following charge-transfer processes on the surface vanadyl group (V=0) of the tetrahedrally coordinated VO4 species involving an electron transfer from to V and a reverse radia-... 

The action spectrum of the photocatalytic isomerization reactions on MgO, defined as the plot of the reaction rate vs the wavelength of the light used, shows a good agreement with the absorption spectrum, i.e., the photoluminescence excitation spectrum of the MgO (96-98, 248). The addition of O2 or CO to MgO led to the quenching of the photoluminescence. Similarly, the rates of the photocatalytic isomerization reactions on MgO were easily inhibited by the addition of CO. its extent increasing with an increase in CO pressure. 

Figure 5. Photoluminescence spectra of K4Nb60 7 taken at 77 K (a) emission, excited at 320 nm (b) excitation spectrum recorded at 440 nm. Optical absorption spectrum is shown in (c). From J.A. Sanz-Garcia, E. Dieguez and C. Zaldo, Phys. Status. Solidi 1988, 108, K145. Reproduced by permission of Wiley-VCH.

Figure 3.23. Absorption spectrum (solid line) and photoluminescence spectrum obtained after simultaneous TPA (dashed line) of methyl-substituted ladder-type poly(para-phenylene) film at room temperature under vacuum of < 10 5 Torr using pulses of a Ti sapphire amplifier laser that have a width of 140 fs and a repetition rate of 1 kHz and intensities of up to 6 mW for pump energies in the range 1.55-2.00 eY. (From Ref. [386] with permission of Elsevier.)...

FIGURE 12.14 Shown are the absorption and photoluminescence from Ru(dcb)(bpy)2/Ti02 immersed in acetonitrile. The addition of LiC104 to the acetonitrile resulted in a red shift in the absorption spectrum (shown by dotted line) and aquenching of the photoluminescence intensity that was shown to result from oxidative quenching by the conduction band. Time-resolved data were most consistent with the model shown Li+ adsorption to Ti02 promotes rapid excited-state injection. 

Fig. 12.4 Photoluminescence of host materials and absorption spectrum of DCM2 (a), and absorption coefficients of the host materials (b). The vertical line indicates the pump wavelength.

Fig. 12.6 Spectra of second-order DFB lasers and tuning ranges together with the corresponding photoluminescence (dashed) spectra, for NPD DCM2 (a), CBP DCM2 (b), and Alq3 DCM2 (c). The absorption spectrum of DCM2 is given as the dotted curve.

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