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

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 sila-graphene,” 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(n-butylsilyne) 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.