Band gap optical

Table 1. Optical Band Gaps For Conjugated Polymers...

The scope of Wessling route has been extended by Mullen and co-workers to develop a soluble precursor route to poly(anthrylene vinyiene)s (PAVs) [51]. It was anticipated that the energy differences between the quinoid and aromatic resonance structures would be diminished in PAV relative to PPV itself. An optical band gap of 2.12 eV was determined for 1,4-PAV 29, some 0.3 eV lower than the value observed in PPV. Interestingly, the 9, lO-b/.v-sulfonium salt does not polymerize, possibly due to stcric effects (Scheme 1-9). 

Numerous ternary systems are known for II-VI structures incorporating elements from other groups of the Periodic Table. One example is the Zn-Fe-S system Zn(II) and Fe(II) may substimte each other in chalcogenide structures as both are divalent and have similar radii. The cubic polymorphs of ZnS and FeS have almost identical lattice constant a = 5.3 A) and form solid solutions in the entire range of composition. The optical band gap of these alloys varies (rather anomalously) within the limits of the ZnS (3.6 eV) and FeS (0.95 eV) values. The properties of Zn Fei-xS are well suited for thin film heterojunction-based solar cells as well as for photoluminescent and electroluminescent devices. 

The ECALE synthesis of V-VI (V Sb, Bi) compounds has been attempted in a few works. Antimony telluride, Sb2Te3, nanofilms with a homogeneous microstructure and an average size of about 20 nm were formed epitaxially on a Pt substrate [61]. The optical band gap of these films was blue-shifted in comparison with that of the bulk single-crystal Sb2Tc3 compound. 

Optical band gap energies (Eg) for WOx-ZrOa samples calcined at 1073 K were obtained from UV-vis spectra using procedures based on direct and indirect transitions between valence and conduction bands [26]. Direct band gap energies (Egdecreased monotonically from 4.15 to 3.75 eV as the W loading increased from 3.05 to 15.0 W-atomsnm (Table 2). 

Perhaps the most simple crystals in this class are the alkaline earth oxides. They are II-VI compounds and have rocksalt crystal structures. Data for their hardnesses versus their bond moduli (optical band gaps per molecular volumes) are displayed in Figure 11.4. 

CdSe, CdTe. CdSe films have been grown from complexed (with tartaric acid and triethanolamine) cadmium acetate or cadmium sulfate solutions and sodium selenosullale.1272 81 84 The films were amorphous or nanocrystalline with an average crystallite size of 6nm. The optical band gap was 1.8-2.1 eV, and the electrical resistivity was of the order 104-106Qcm. 

Cadmium acetate and sodium tellurite solutions have similarly been used to grow CdTe films by SILAR. The films were polycrystalline (hexagonal), and the grain size was on the order of 22nm (film thickness 272nm). The optical band gap was 1.41 eV.85... 

The recently synthesized PPV 68, in which the oxadiazole group is separated from the PPV backbone by an oxygen atom, is a very soluble material with optical band gap of 2.36 eV and yellowish-orange emission color (chromaticity coordinates by the Commission Internationale de l Eclairage, CIE a 0.50, y = 0.47 591 nm) [124]. An extremely high-... 

The band gap, determined as the onset of the absorption band in thin films is 2.95 eV (425 nm). Janietz et al. [252] used the onset of the redox waves in CV experiments to estimate the /P and Ea energies of the dialkyl-PFs (Figure 2.11). The gap between the obtained energy levels (5.8 eV for 7P and 2.12 eV for EA) IP—EA 3.8 eV is substantially higher than the optical band gap. Although optical absorption and electrochemistry test two physically different processes (vertical electron excitation and adiabatic ionization) and are not expected to be the same,... 

The ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS) measurements are used to calculate /P of PFO at — 5.6 +0.05 eV, and the band gap at 3.1 +0.1 eV, which is also much closer to the optical band gap than to the value deduced from the electrochemistry in films [254]. Thus, the HOMO LUMO levels of PF can be reasonably well-matched by work functions of ITO/PEDOT (—5.1eV) and Ca electrode (ca. — 2.9 eV), respectively. However,... 

The EL of poly(o-phenylene ethynylene) 522 was reported by Onoda and coworkers [637], As expected, the optical band gap of 522 (3.1 eV) is larger than that of para-connected polymer 516, making the former a blue-purple-emitting material (APL = 400). Interestingly,... 

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