Photoluminescence, silicon polymers

P. M. Fauchet, Porous Silicon Photoluminescence and Electroluminescent Devices C. Delerue, G. Allan, and M. Lannoo, Theory of Radiative and Nonradiative Processes in Silicon Nanocrystallites L. Bros, Silicon Polymers and Nanocrystals... 

Properties such as photoconduc.tivityl l t l and photoluminescence of silicon polymers have been reported because of their wider optical band gap compared with crystalline silicon. Theoretical investigations of silicon polymers have been also reported ll2l-[21] Xakeda, Matsumoto and Fukuchi calculated the electronic structure of polysilane chains using the semi-empirical approach called the Complete Neglect of Differential Overlaps (CNDO) Molecular-Orbital (MO) method They discussed the dependence of the size and... 

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The incorporation of siloles in polymers is of interest and importance in chemistry and functionalities. Some optoelectronic properties, impossible to obtain in silole small molecules, may be realized with silole-containing polymers (SCPs). The first synthesis of SCPs was reported in 1992.21 Since then, different types of SCPs, such as main chain type 7r-conjugated SCPs catenated through the aromatic carbon of a silole, main chain type cr-conjugated SCPs catenated through the silicon atom of a silole, SCPs with silole pendants, and hyperbranched or dendritic SCPs (Fig. 2), have been synthesized.10 In this chapter, the functionalities of SCPs, such as band gap, photoluminescence, electroluminescence, bulk-heterojunction solar cells, field effect transistors, aggregation-induced emission, chemosensors, conductivity, and optical limiting, are summarized. 

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. 

Crystalline silicon is the most widely used semiconductor material today, with a maiket share of above 90%. Because of its indirect electronic band structure, however, the material is not able to emit light effectively and therefore carmot be used for key applications like light-emitting diodes or lasers. Selected one- or two-dimensional silicon compounds like linear or branched polysilylenes [1] or layered structures like siloxene [2], however, possess a direct band gap and therefore exhibit intense visible photoluminescence. Siloxene, a solid-state polymer with a sheet-like layered structure and an empirical formula Si H (OH) , in particular, is considered as an alternative material for Si-based liuninescent devices. Detailed studies of stmctural and photophysical properties of the material, however, are strraigly impeded by its insolubility in organic solvents. 

Poly-p-phenylene-vinylene-based polymers containing a silicon atom in the main chain are of great interest because of their efficient photoluminescence and potentially useful electroluminescence properties [34]. Poly(phenylene-vinylene-silylene)s are usually synthesized by polyhydrosilylation... 

Gongalsky MB, Kharin AY, Osminkina LA, Timoshenko VY, Jeong J, Lee H, Chung BH (2012) Enhanced photoluminescence of porous silicon nanoparticles coated by bioresorbable polymers. Nanoscale Res Lett 7 446... 

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Deposition of polymer layers on the porous stracture has similar effects and changes the stability and sensitivity of PSi-based devices as well (Vrkoslav et al. 2005 Xia et al. 2005 Benilov et al. 2007). For example, Xia et al. (2005) established that PDMS (polydimethylsiloxane) monolayers provide good protection and some characteristic improvement for PL of PSi. The measurements have shown that the PDMS monolayer provided a strong armature to PSi under a variety of stringent conditions such as in the base solution. Vrkoslav et al. (2005) also showed that impregnation of porous silicon with cobalt phthalocyanine (Co"Pc) is an effective way to improve the stability of the photoluminescence quenching response. 

The high sensitivity of the silicon atom offers new synthetic routes to polythiophene. As shown by infiared, Raman and photoluminescence criteria, silicon activates the selective coupling of thiophene units, leading to highly conjugated polymers with improved physical properties. 

ABSTRACT. Band calculated results for electronic structures of sigma-conjugated polymers are reviewed. Conformational and substitutional effects for polysilanes are calculated theoretically and are discussed in the light of experimental data from UV absorption and photoluminescence. The electronic structures of hetero-copolymers of polysilane and polygermane, corresponding to the 1-dimensional superlattice structure, are described. Two-dimensional silicon network polymers are studied theoretically and experimentally. 

It is well known that visible luminescence is observed even in some kinds of polysilanes. In methylnaphtylpolysilane, visible emission is observed from die excimer sites formed by the stacking of naphtyl sidechains. In mediylphenylpolysilane, the visible emission is due to a n interaction between the silicon backbone and phenyl sidechains. Silicon network polymers, however, exhibited no marked differences in photoluminescence spectra, regardless of their sidechains. This indicates that photoluminescence originates from the silicon backbone itself. 

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. 

Using Dye/amine/alkyl bromide, iridium-containing photoluminescent polyacrylate films have also been manufactured. Polyoxometallate (POM)/polymer hybrid materials exhibiting modified mechanical properties (polymerized EPOX/TMPTA matrix with inserted POM clusters [XIA 15]) were synthesized in a one-step process using a silicon or phosphor polyoxomolybdate/iodonium salt/silane system. 

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