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.

Characterization and application of calcium ferrites based solid solutions containing active oxygen species for catalysts in propylene total and methane partial oxidation has been studied. The calcium ferrite based solutions containing brownmillerite phases showed a structural transition based on the migration of oxide ions at high temperature. The calcium ferrite solution provided two types of active oxygen species due to the existence of the brownmillerite phase. These oxygen species individually played important roles in the propylene and methane oxidation mechanisms.

Recently, we found pure green photoluminescence (PL) at 540 nm (2.34 eV) in a vacuum, which is characteristic of a Si-Si bonded network polymer bearing n-butyl groups (organopolysilyne, SNP). SNP was carefully isolated as an orange-yellow solid by avoidance of contact with air and water in the polymer synthesis and PL measurement. This was in contrast with previous reports that SNPs carrying alkyl groups have a blue PL band around 450-480 nm. By applying the modified technique to a soluble Ge-Ge bonded network polymer carrying n-butyl groups (organopolygermyne, GNP), with much care in synthesising the polymer and measuring the PL, we found that GNP reveals a very brilliant red-coloured PL band at 690 nm (1.80 eV) in a vacuum at 77 K. This was in contrast with a previous report that GNP carrying n-hexyl groups has a green PL band at 560 nm (2.21 eV). On the other hand, soluble Si-Ge network copolymers (SGNPs) prepared in a similar way to SNP and GNP syntheses showed green-and-red dual PL bands at 540 nm and 690 nm. Based on analyses with IR, Raman, HR-TEM, XPS, EELS, UV-Vis and PL data, the dual emission was assumed to originate from the coexistence of Si and Ge domains (1-2 nm in diameter), possibly, in the same skeleton of SGNP.

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