Amorphous polymers photoluminescence

Photoluminescence intensity of the amorphous polymers was generally much larger than that of the more crystalline polymers. The energy level of the lowest singlet excited state Es was evaluated to be 2.5-2.7 eV for the amorphous polymer pristine films, and 2.0 eV for the more crystalline polymers. The Stokes shifts were also observed to be much larger for the amorphous polymer films compared with those of the more crystalline polymer films. This indicates a larger structural relaxation of the amorphous polymers following photoexcitation. 

Hydrogenated amorphous silicon was formed by plasma decomposition of monosilane gas. The network has the dimension of close to 3. Polysilane alloy was formed by plasma decomposition of disilane gas.33 The network consists of a mixture of 1-dimensional polysilane and 3-dimensional silicon micro clusters.34 The effective network dimension is lower than that of amorphous silicon. Photoluminescence observations for various silicon-based materials are shown in Figure 14. The peak energy values of the photoluminescence spectra for amorphous silicon, polysilane alloy, hexyl-silicon network polymer and dihexylpolysilane are 0.8, 1.2, 2.8 and 3.3 eV, respectively. This result confrrms that a wide continuous spectra range from ultraviolet to infrared can be covered by the luminescence spectra of silicon based polymers. 

Crystalline and amorphous silicons, which are currently investigated in the field of solid-state physics, are still considered as unrelated to polysilanes and related macromolecules, which are studied in the field of organosilicon chemistry. A new idea proposed in this chapter is that these materials are related and can be understood in terms of the dimensional hierarchy of silicon-backbone materials. The electronic structures of one-dimensional polymers (polysilanes) are discussed. The effects of side groups and conformations were calculated theoretically and are discussed in the light of such experimental data as UV absorption, photoluminescence, and UV photospectroscopy (UPS) measurements. Finally, future directions in the development of silicon-based polymers are indicated on the basis of some novel efforts to extend silicon-based polymers to high-dimensional polymers, one-dimensional superlattices, and metallic polymers with alternating double bonds. 

In pSiTh-1 film the photoluminescence emission appears as a broad and unresolved structure (Figure 14.31). In some conducting polymers this kind of profile was attributed to disorder , defined in terms of low conjugation length, strong amorphous character and large number of structural defects [123]. 

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