Synthesis and characterization of luminescent properties of ceramics derived from polysilylcarbodiimides

Abstract

The luminescence properties related to the thermal polymer/ceramic conversion behavior of silicon dicarbodiimide {SDC, [Si(N=C=N)2]n} have been investigated. SDC was synthesized by the non-oxidic sol–gel condensation reaction of silicon tetrachloride with bis(trimethylsilyl)carbodiimide. As-synthesized SDC showed no luminescence under UV light, while heat-treated SDC showed an appreciable photoluminescence (PL) and the maximum visible PL emission intensity was achieved by heat treatment at 400°C. Even after the heat treatment up to 970°C, the SDC preserved most of the N=C=N groups to keep whitish gray color without distinct free carbon formation, and emitted visible blue luminescence. The 400°C-heat treated SDC exhibited the intense luminescence excited at 281 and 379 nm wavelengths, while there was no PL emission excited by the N=C=N group-derived host absorption at 214 nm. The PL properties of the heat-treated SDCs could be correlated with their preservation of the local structure including N=C=N groups and defects formation during the heat treatment. Moreover, Eu3+-modified SDC was prepared by the same sol–gel method using Eu(III) chloride as the Eu3+-source. The results of FT-IR and 29Si NMR spectroscopic analyses revealed a complex formation between the Eu(III) chloride and bis(trimethylsilyl)carbodiimide. As a result, the Eu3+-modified SDC exhibited a characteristic PL red emission at around 600 nm attributed to the f-f-transition of Eu3+.