Full-Visible-Spectrum Emitters from Pyrolysis of Soluble Si−Si Bonded Network Polymers

Abstract

Crystalline silicon is a poor UV-visible-near IR emitter because of its indirect, narrow band gap and low quantum yield of ∼1 × 10 -2 % at room temperature. To effectively confine a photoexcited electron-hole pair (exciton) within Si's Bohr radius of ∼5 nm, we have theoretically and experimentally explored several low-dimensional Si-based materials. Although Si-Si bonded network polysilyne was previously regarded as a soluble model polymer of amorphous Si and Si nanosheet-like "saturated silagraphene," further studies on pyrolytic products of polysilyne derivatives and their inherent photophysical properties under a vacuum have not yet been reported. The present paper demonstrated visible light emission from ten soluble polysilynes in the range 460 nm (2.70 eV) to 740 nm (1.68 eV) at both 77 K and room temperature by controlling temperature and time of the pyrolysis (200-500 °C, 10-90 min) under a vacuum. When very weakly deep-red emitting Si particles produced by the pyrolysis of poly(nbutylsilyne) at 500 °C for 90 min were exposed to air, the photoluminescence switched abruptly to an intense sky-blue color (λ ) 430 nm), with a quantum yield of 20-25% and a short lifetime of ∼5 ns in common organic solvents at room temperature because of the Siloxene-like, multilayered Si-sheet structures.

Investigation of photoluminescence of Si−O−C(−H) ceramics at an early stage of decarbonization by using high energy excitation

“…Various kinds of Si−O−C ceramics were synthesized by various methods, and many mechanisms have been proposed to explain the observed PL bands. [3][4][5][6][7][8][9] Their simple chemical composition with no special activator was promising for their use in LED systems, devices of radiation detectors or environmental resistant inorganic pigments with fluorescent colors.…”

Air-stable poly(3,3,3-trifluoropropylsilyne) homo- and copolymers

“…Although this subtle splitting may be ascribed to certain polymer structural irregularity and/or terminal effects, it is also possible to compare this splitting value with a doubly split signal with J F-Si z 32 Hz of chain-like PMFS in less polar toluene-d 8 . 40 In contrast, the very highly restricted Si skeletal motion is evident from the very broad 29 Si NMR signals of FSNP, F 0.5 B 0.5 SNP, and BSNP in CDCl 3 at 25 C, which ranged from À50 to À80 ppm ( Fig. S2 †).…”

“…S6, † the F-element white images are more intense than the Si-element white images, which reflects the 3 : 1 ratio between F and Si atoms per repeating unit of FSNP. Nevertheless, the tandem NMR ( 1 H, 19 F, 29 Si), XPS, IR and Raman characterizations cannot provide a definitive answer to Table S1 † and Fig. 2 that the resulting FBSNP is composed of small-sized FSi and BSi domains, as illustrated in Fig.…”

“…4 As an alternative approach, we have demonstrated that a carefully controlled pyrolysis of various SNPs makes them visible PL emitters in the range of 430 to 740 nm. 29 SNP with an n-butyl group (BSNP) showed a pure-green PL at 540 nm (2.34 eV); this material was carefully isolated as an orange-yellow solid by avoiding contact with air and water during the polymer synthesis and PL measurements. These results were very different from those of other authors, who reported that SNPs that carry n-hexyl and oligoether side groups exhibit a blue PL at approximately 450-480 nm (2.58-2.76 eV) in solution at room temperature and at 480 nm (2.58 eV) in the film state at 77 K. [26][27][28] Watanabe reported that the pyrolysis products of soluble nc-Si particles capped with t-butyl groups provide PL emitters in the visible region and that the PL wavelength varies with pyrolysis temperature under vacuum.…”

Solution-processed amorphous silicon surface passivation layers

“…First experiments with liquid polysilane precursors such as cyclopentasilane 6 , neopentasilane 7 or trisilane 8 were conducted to manufacture a variety of structures and devices. Amorphous silicon (a-Si:H) thin films were applied in solar cells 9,10 , light-emitting devices 11 and thin-film transistors 6 . Furthermore crystalline silicon nanowires were used as anode material in lithium batteries 12 .…”