Tauc relation

UV-vis absorption spectra of Alq(l) and Alq(2) were studied in the solution and in thin films. No difference was observed in the main absorption peaks in solution and thin films. The absorption and PL measured in the solution and in thin films of the complexes are shown in Fig. 4.14. The synthesized complexes showed strong green emission in the range 522-523 nm. The optical band gap of the materials were determined from absorption edge and using the Tauc relation, which relates the absorbance A, with the band gap as... 

The analysis of the shape of the absorption edge of the high-pressure phase (Fig. 13) shows the existence of two spectral ranges with different types of energy dependence on the absorption coefficient. At high values of absorption it follows the empirical Tauc relation [57] in the case of parabolic band edges (Fig. 13(b)), while at smaller absorption a so-called Urbach or exponential absorption tail [58, 59] is observed (Fig. 13(c)). The existence of this kind of absorption edge is normally related to amorphous semiconductors. The optical absorption gap determined from our experiment is 0.6-0.7 eV and it decreases with pressure (see below). The slope of the Urbach tail, which can be considered as a measure of a random microfield [59] is found to be T=2.6 eV at 160 GPa. This is very close to what one would expect for an amorphous phase with a coordination of 2.5 [59]. 

FIG. 69. Relation between the optical bandgap (Tauc convention) and the hydrogen content in rt-Si H deposited by HWCVD (closed circles) and PECVD (open triangles). (From K. F. Feenstra. Ph.D. Thesis, Universiteit Utrecht. Utrecht, the Netherlands. 1998. with permission.)... 

A detailed band gap analysis involves plotting and fitting the absorption data to the expected trendlines for direct and indirect band gap semiconductors. Ideally, the absorbance A is first normalized to the path length I of the light through the material to produce the absorption coefficient a as per Eq. (5.3). Values of a > 10" cm often obey the following relation presented by Tauc and supported by Davis and Mott [4, 5] ... 

Polarization and absorption are interconnected by the Kramers-Kronig dispersion relation (cf. e.g. Tauc (1965))... 

If the surface oxide is of a semiconducting composition (e.g., MoOj, V2O5, and WO3), its electronic band structure can be probed through optical absorption spectroscopy [78]. UV-visible (vis) diffuse reflectance measurement of powders enables experimental determination of the optical absorption gap most commonly estimated through Tauc s relation [33,79-81 ], although other methods exist [80-82]. A Tauc plot linearly extrapolates versus E to zero absorption to... 

Optical Characterization UV-Vis absorption spectra were obtained with a Shimadzu Asia Pacific Ltd. (Singapore) UV-1800 spectrophotometer. UV-Vis absorption spectra of CdSe, CdTe and ZnSe nanoparticles are shown in Fig. 19. The absorption spectra of the CdSe nanoparticles were considered without taking into account the reflection losses. The Tauc equation relates the absorption coefficient a(v) due to inter-band transitions near the band edge to the incident photon energy by... 

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