High-temperature photoluminescence in sol-gel silica containing SiC/C nanostructures

Silicon carbide and carbon nanostructures were produced by pyrolysis of org anosilane or aromatic compounds in nanoporous sol-gel silica glasses. Inten se photoluminescence was observed in the visible and the near infrared regi ons, depending on material processing. Emission bands at 2.97, 2.67, 2.53, 2.41, 2.24, 2.09, 1.93, 1.13, 1.00, and 0.85 eV were observed in samples pr epared at temperatures between 870 and 1220 K. Phosphorescence emission sho wed two lifetime components at 300 K: a 0.03 s component and a very long co mponent of 0.5-4 s that depends on the precursors and sample processing. Th ese lifetimes approximately doubled at 77 K. The visible emission increased significantly as the temperature was elevated from 77 to 950 K, suggesting thermally assisted light emission from sites in the silica glasses contain ing SiC/C nanostructures. Surface SIC vacancy defects modeled using integra ted nb initio quantum mechanics/molecular mechanics calculations suggest ph osphorescence may originate from C vacancy (Si-Si dimers) in the visible an d Si vacancy in the near infrared. (C) 2000 American Institute of Physics. [S0003-6951(00)01217-1].